From the Northern Hemisphere, the bright star Vega is easy to spot on May evenings. Go outside on a May evening, and face northeast. You’ll easily notice Vega, a bright blue-white star. If your sky is dark, you might also see its constellation Lyra the Harp. In its journey around the galaxy, our sun moves toward bright Vega. The point toward which we move is called the apex of the sun, aka the solar apex. Image via EarthSky.
Our star, the sun, and its planets are moving through space in the general direction of the bright star Vega. Astronomers call the sun’s direction of motion by a great old name: the solar apex or, more romantically, the apex of the sun’s way.
And the month of May is a great time to visualize our sun’s motion through space, if you live in the Northern Hemisphere. In May, our Milky Way galaxy lies as flat around the horizon as it can. And the star Vega – which is near the solar apex on the sky’s dome – is ascending in the northeast on May evenings for Northern Hemisphere viewers.
Can you see Vega from the Southern Hemisphere, too? Yes, but, from southerly latitudes, it isn’t up in early evening in May. That’s because, at that time of the night, the body of Earth itself blocks it from the view of southern observers. If you’re in the Southern Hemisphere, you can see Vega, but you’ll need to look later at night. Look here for details on the differences in seeing Vega from Northern and Southern Hemisphere locations, in May.
Where is the solar apex in our sky?
The solar apex isn’t exactly in Vega’s direction. It’s located in our sky in the direction of a constellation that’s harder to pick out … the constellation Hercules. This constellation is southwest of the star Vega and its constellation Lyra. It’s a location on the celestial sphere with these coordinates: 18h 28m 0s in right ascension, 30° N in declination.
How do we know our sun is moving in this direction? Astronomers find this point on our sky by measuring the motions of stars near the sun.
A star chart showing the location of the solar apex in the sky. It’s not far from Vega. Image via Stellarium. Used with permission.
Sun’s motion in its galactic neighborhood
Think back to when you last walked on a busy sidewalk. In general, most people are walking at a similar pace. At a distance, they look close together. But if you pick up your pace when walking toward them, people appear to be moving apart.
As the sun travels along its galactic sidewalk with neighboring stars, it moves slightly faster than the mean velocity of its neighbors. If you could fast-forward over several hundred thousand years, you’d notice the following: nearby stars appear to move away from the solar apex. On the opposite side of the celestial sphere, called the antapex, you’d see the opposite: the distance between stars in the sky appears to get smaller.
You can see this effect in an animation from the European Space Agency, based on data from the Gaia space telescope. Scientists extrapolated the motion of 40,000 stars over 1.6 million years to see how they would appear to move in the sky. All these stars had known motions that Gaia measured and were within 326 light-years of the sun.
The trails show how far the stars move on the celestial sphere. It’s a busy animation. But if you look closely, you’ll notice, towards the end, many (not all) stars on the upper left appear to be moving away from a central point. That’s the solar apex. And on the right, they appear to be getting closer to each other. That’s the antapex, which is opposite on the sky from the solar apex. You can read more about this video the at ESA website.
Looking toward the apex of the sun
Vega is a bright star. So you can look for it and find it pretty easily, from Northern Hemisphere locations, in the northeast in early evening in May. By the predawn and dawn hours, the Southern Hemisphere can see Vega, too. Look north from the Southern Hemisphere before dawn.
To see a precise view – and time – for Vega from your location, try Stellarium Online.
Then look for the star Vega and contemplate the fact that our sun and family of planets travel more or less toward it.
With its blue-white color, Vega also happens to be one of the loveliest stars you’ll ever see.
The blue-white star Vega is near the apex of the sun’s way, our sun’s direction of motion through space. Image via Fred Espenak at AstroPixels.com. Used with permission.
Sun’s motion in our galaxy
A friend from Australia wrote:
I seek to find out what speed our sun is traveling at and also how many years it takes to circumnavigate the galaxy.
Our sun takes a long time to circumnavigate the Milky Way, which is a collection of several hundred billion stars with an estimated diameter of about 100,000 light-years. There are various estimates for the speed the sun travels through the galaxy, but its speed is in the range of about 140 miles per second (225 km/sec).
Likewise, there are multiple estimates for the length of time it takes the sun to complete one circuit of the galaxy, but a typical estimate is about 230 million years.
That period of time – the length of the sun’s orbit around the Milky Way’s center – is sometimes called a cosmic year.
What is the solar antapex?
The solar antapex is located opposite the solar apex on the celestial sphere, near the bright star Sirius. Therefore, our sun and planets travel more or less away from Sirius (that’s in the constellation Canis Major). Sirius is the sky’s brightest star. Not surprisingly, Vega and Sirius lie in opposite directions in Earth’s sky.
You can look for Sirius at this time of year, too. Remember, Vega resides almost exactly opposite Sirius. If you have an unobstructed horizon, this evening you might see Sirius low in the southwest as Vega rises low in the northeast (at mid-northern latitudes).
At mid-northern latitudes, you’ll possibly see both stars around 8:30 to 9 p.m. local time (the time on your clock wherever you are) in May.
Use the 3 stars of Orion’s Belt to find Sirius, the brightest star of the nighttime sky. From mid-latitudes in the Northern Hemisphere, you might see Sirius low in the southwest, as Vega rises in the northeast.
Bottom line: Our sun – and solar system – are moving in space in the general direction of the solar apex, which is located near the star Vega.
From the Northern Hemisphere, the bright star Vega is easy to spot on May evenings. Go outside on a May evening, and face northeast. You’ll easily notice Vega, a bright blue-white star. If your sky is dark, you might also see its constellation Lyra the Harp. In its journey around the galaxy, our sun moves toward bright Vega. The point toward which we move is called the apex of the sun, aka the solar apex. Image via EarthSky.
Our star, the sun, and its planets are moving through space in the general direction of the bright star Vega. Astronomers call the sun’s direction of motion by a great old name: the solar apex or, more romantically, the apex of the sun’s way.
And the month of May is a great time to visualize our sun’s motion through space, if you live in the Northern Hemisphere. In May, our Milky Way galaxy lies as flat around the horizon as it can. And the star Vega – which is near the solar apex on the sky’s dome – is ascending in the northeast on May evenings for Northern Hemisphere viewers.
Can you see Vega from the Southern Hemisphere, too? Yes, but, from southerly latitudes, it isn’t up in early evening in May. That’s because, at that time of the night, the body of Earth itself blocks it from the view of southern observers. If you’re in the Southern Hemisphere, you can see Vega, but you’ll need to look later at night. Look here for details on the differences in seeing Vega from Northern and Southern Hemisphere locations, in May.
Where is the solar apex in our sky?
The solar apex isn’t exactly in Vega’s direction. It’s located in our sky in the direction of a constellation that’s harder to pick out … the constellation Hercules. This constellation is southwest of the star Vega and its constellation Lyra. It’s a location on the celestial sphere with these coordinates: 18h 28m 0s in right ascension, 30° N in declination.
How do we know our sun is moving in this direction? Astronomers find this point on our sky by measuring the motions of stars near the sun.
A star chart showing the location of the solar apex in the sky. It’s not far from Vega. Image via Stellarium. Used with permission.
Sun’s motion in its galactic neighborhood
Think back to when you last walked on a busy sidewalk. In general, most people are walking at a similar pace. At a distance, they look close together. But if you pick up your pace when walking toward them, people appear to be moving apart.
As the sun travels along its galactic sidewalk with neighboring stars, it moves slightly faster than the mean velocity of its neighbors. If you could fast-forward over several hundred thousand years, you’d notice the following: nearby stars appear to move away from the solar apex. On the opposite side of the celestial sphere, called the antapex, you’d see the opposite: the distance between stars in the sky appears to get smaller.
You can see this effect in an animation from the European Space Agency, based on data from the Gaia space telescope. Scientists extrapolated the motion of 40,000 stars over 1.6 million years to see how they would appear to move in the sky. All these stars had known motions that Gaia measured and were within 326 light-years of the sun.
The trails show how far the stars move on the celestial sphere. It’s a busy animation. But if you look closely, you’ll notice, towards the end, many (not all) stars on the upper left appear to be moving away from a central point. That’s the solar apex. And on the right, they appear to be getting closer to each other. That’s the antapex, which is opposite on the sky from the solar apex. You can read more about this video the at ESA website.
Looking toward the apex of the sun
Vega is a bright star. So you can look for it and find it pretty easily, from Northern Hemisphere locations, in the northeast in early evening in May. By the predawn and dawn hours, the Southern Hemisphere can see Vega, too. Look north from the Southern Hemisphere before dawn.
To see a precise view – and time – for Vega from your location, try Stellarium Online.
Then look for the star Vega and contemplate the fact that our sun and family of planets travel more or less toward it.
With its blue-white color, Vega also happens to be one of the loveliest stars you’ll ever see.
The blue-white star Vega is near the apex of the sun’s way, our sun’s direction of motion through space. Image via Fred Espenak at AstroPixels.com. Used with permission.
Sun’s motion in our galaxy
A friend from Australia wrote:
I seek to find out what speed our sun is traveling at and also how many years it takes to circumnavigate the galaxy.
Our sun takes a long time to circumnavigate the Milky Way, which is a collection of several hundred billion stars with an estimated diameter of about 100,000 light-years. There are various estimates for the speed the sun travels through the galaxy, but its speed is in the range of about 140 miles per second (225 km/sec).
Likewise, there are multiple estimates for the length of time it takes the sun to complete one circuit of the galaxy, but a typical estimate is about 230 million years.
That period of time – the length of the sun’s orbit around the Milky Way’s center – is sometimes called a cosmic year.
What is the solar antapex?
The solar antapex is located opposite the solar apex on the celestial sphere, near the bright star Sirius. Therefore, our sun and planets travel more or less away from Sirius (that’s in the constellation Canis Major). Sirius is the sky’s brightest star. Not surprisingly, Vega and Sirius lie in opposite directions in Earth’s sky.
You can look for Sirius at this time of year, too. Remember, Vega resides almost exactly opposite Sirius. If you have an unobstructed horizon, this evening you might see Sirius low in the southwest as Vega rises low in the northeast (at mid-northern latitudes).
At mid-northern latitudes, you’ll possibly see both stars around 8:30 to 9 p.m. local time (the time on your clock wherever you are) in May.
Use the 3 stars of Orion’s Belt to find Sirius, the brightest star of the nighttime sky. From mid-latitudes in the Northern Hemisphere, you might see Sirius low in the southwest, as Vega rises in the northeast.
Bottom line: Our sun – and solar system – are moving in space in the general direction of the solar apex, which is located near the star Vega.
Baily’s beads are beads of sunlight caused when sunlight shines between mountains and other features on the moon. These Baily’s beads are from the February 16, 1991, annular solar eclipse. Image via Fred Espenak, aka Mr Eclipse. Used with permission.
May 15, 1836: On this date in science, Francis Baily (1774-1844), an English astronomer, saw beads of sunlight shining along the edge of the moon’s silhouette during an eclipse of the sun.
It was an annular eclipse – nowadays often called a ring of fire eclipse – meaning that the moon was too far away in its monthly orbit around Earth to appear large enough in our sky to cover the sun completely. Baily saw beads of light shining around the darkened lunar limb (edge of the moon).
Another shot of Bailey’s beads from the February 16, 1999, eclipse. Image via Fred Espenak. Used with permission.
Baily’s discovery
Baily’s goal was to time the length of the annular phase of the eclipse. He would do this by recording the time during which the moon was inside the sun’s disk. He would start timing as soon as a line of sunlight appeared along the trailing edge of the moon.
Baily expected to observe a nice, smooth line of sunlight along one edge of the moon. Imagine his surprise as he watched and waited for it to appear – while observing with a filtered 2.6-inch, f/16 refracting telescope – at 40x magnification. Instead of seeing a smooth line of sunlight, he saw a broken line of light and dark spots.
Don’t start that stopwatch yet, Mr. Baily!
Baily and others have commented that the line of light and dark spots resembled beads on a string. And, as the seconds ticked by, Baily saw the dark spots decrease in both number and size. And he saw the light spots increase in both number and size, until there was a fine line of sunlight around the edge of the moon.
Okay, now start the stopwatch!
But after the moon was completely inside the solar disk, the moon did look “smooth and circular” to him. At least four other local observers confirmed this observation during this eclipse.
Sunlight shining through lunar valleys
Later, others realized that these beads of light appeared due to mountains and valleys, crater walls, and other topographic features extending above the limb, or edge, of the moon as seen from Earth. This phenomenon earned the name Baily’s beads. And you can see it during total eclipses, too, just before the moon covers the sun completely. A video of Baily’s beads is here.
Baily published his discovery in the Monthly Notices of the Royal Astronomical Society in December of 1836. In a talk to the Royal Astronomical Society, he mentioned that he knew of only one other person who had seen these before, that being Jean Henri van Swinden (1746–1823), a Dutch scientist.
Today, Baily’s beads are one of the eclipse effects that amateur astronomers around the world – using proper eye protection – watch for during annular and total eclipses of the sun.
Francis Baily, for whom Baily’s beads are named. Image via Wikimedia Commons.
Baily’s beads during a total eclipse
Baily discovered the beads during an annular eclipse, but they’re best known for being visible during a total eclipse. Let’s look at the process during a total eclipse.
During a total eclipse, the moon moves across a sun that takes up the same amount of sky. As the leading edge of the moon moves toward covering the remainder of the sun, dark spots interrupt the last bit of sunlight. Those are lunar mountains. Totality has not yet begun, as sunlight is still peeking between these dark spots.
As the seconds tick by, the sunlight decreases, and the dark areas increase until there is only one spot of light on the limb of the moon: the diamond ring. When that final bright spot disappears, the total eclipse begins. Remove the solar filters for a fantastic view.
As the total phase draws to a close, the effects resume in reverse order. On the trailing side of the moon the sunlight appears. First, the diamond ring. Next, Baily’s beads. Watch a video of Baily’s beads during the August 21, 2017, total eclipse here.
The Baily’s beads phase is unappreciated during total eclipses. The main show is totality, and observers are typically preparing to remove their solar filters while Baily’s beads and the diamond ring are occurring. And those Baily’s beads at the end of totality? They are accompanied by sighs as the total phase comes to an abrupt end. But you can watch the phenomena at the end of the total eclipse with unfiltered and dark-adapted eyes, so they might appear brighter and more noteworthy than those leading into the total phase.
Baily’s beads, visible during a total eclipse of the sun. Here, you’re almost seeing another effect, known as the diamond ring. Image via Luc Viatour/ Encyclopedia Britannica.
Baily’s beads during an annular eclipse
Here is the process during an annular eclipse, the type that Baily saw. To start, the moon appears smaller than the sun, so you must use filters the entire time. At the center of the annular eclipse, you see a ring of the sun around the moon. And the episode begins on the trailing, not the leading, edge of the moon. As the last bit of the moon moves onto the sun, the uneven dark limb (edge) of the moon produces bright spots. These bright spots increase in number and size until the whole edge of the moon is a bright arc of sunlight.
That is what Baily saw. Toward the end of the annular phase of the eclipse, now looking toward the leading edge of the moon, that bright arc of sunlight begins to be interrupted by dark spots, growing in size. A video of Baily’s beads during an annular eclipse is here.
Extending the beads
Is there a way to make those beads visible for a longer length of time? Yes, there are two ways. One is to hop onto a jet and zoom along the path of the eclipse. This will also extend the length of the total phase of the eclipse.
The other way is to set up near the edge of the central path of the eclipse. The typical eclipse shows the main event, whether annular or total, only along a path on the earth that is about 100 miles (160 km) wide. Sit in the center of that path and the eclipse phase will last longer than near the north or south limit of this path. But if you go near the north or south limit, the Baily’s beads phase will last longer, at the sacrifice of the central phase. A video of Baily’s beads lasting more than two minutes is here.
Petr Horalek took these images from the La Silla Observatory in Chile during the July 2, 2019, total eclipse. He was near the edge of the path of totality. Image via Petr Horalek. Used by permission.
Baily’s beads or Halley’s beads?
On April 22, 1715 (Julian calendar, or May 3, 1715, Gregorian calendar) Edmond Halley (1656-1742) observed a total solar eclipse from London. He predicted the eclipse, and so it is often referred to as Halley’s Eclipse. During this total eclipse, Halley observed Baily’s beads too, 59 years before Baily was even born. Here is Halley’s description:
About two Minutes before the Total Immersion, the remaining part of the Sun was reduced to a very fine Horn, whose Extremeties seemed to lose their Acuteness, and to become round like Stars … which Appearance could proceed from no other Cause but the Inequalities of the Moon’s Surface, there being some elevated parts thereof near the Moon’s Southern Pole, by whose Interposition part of that exceedingly fine Filament of Light was intercepted.
This is an excellent description of Baily’s beads, even though Halley hit the “shift” key a few too many times!
Edmond Halley was the first to observe and identify the event we now call Baily’s beads, yet they are not named after him. What is named after Edmond Halley?
Halley’s Comet, which he did not discover, but he did predict its return. Halley’s Eclipse in 1715, which he also predicted. Halley, the crater on the moon, named long after Halley passed away. Halley, the crater on Mars, named in 1973. Halley Research Station, in Antarctica, established in 1956. Edmond Halley never went to Antarctica, nor to the moon nor Mars, for that matter. Halley’s Mount, a hill on the island of Saint Helena, from where Halley observed the southern sky.
But we don’t have “Halley’s beads,” even though he discovered and defined them. One suggestion is to refer to the beads seen during the annular eclipses as Baily’s beads and the ones seen during the total eclipses as Halley’s beads. Then Edmond Halley would finally be recognized for something he discovered.
Bottom line: May 15, 1836: Francis Baily, an English astronomer, saw light shining through lunar ridges during an eclipse of the sun. These are now known as Baily’s beads.
Baily’s beads are beads of sunlight caused when sunlight shines between mountains and other features on the moon. These Baily’s beads are from the February 16, 1991, annular solar eclipse. Image via Fred Espenak, aka Mr Eclipse. Used with permission.
May 15, 1836: On this date in science, Francis Baily (1774-1844), an English astronomer, saw beads of sunlight shining along the edge of the moon’s silhouette during an eclipse of the sun.
It was an annular eclipse – nowadays often called a ring of fire eclipse – meaning that the moon was too far away in its monthly orbit around Earth to appear large enough in our sky to cover the sun completely. Baily saw beads of light shining around the darkened lunar limb (edge of the moon).
Another shot of Bailey’s beads from the February 16, 1999, eclipse. Image via Fred Espenak. Used with permission.
Baily’s discovery
Baily’s goal was to time the length of the annular phase of the eclipse. He would do this by recording the time during which the moon was inside the sun’s disk. He would start timing as soon as a line of sunlight appeared along the trailing edge of the moon.
Baily expected to observe a nice, smooth line of sunlight along one edge of the moon. Imagine his surprise as he watched and waited for it to appear – while observing with a filtered 2.6-inch, f/16 refracting telescope – at 40x magnification. Instead of seeing a smooth line of sunlight, he saw a broken line of light and dark spots.
Don’t start that stopwatch yet, Mr. Baily!
Baily and others have commented that the line of light and dark spots resembled beads on a string. And, as the seconds ticked by, Baily saw the dark spots decrease in both number and size. And he saw the light spots increase in both number and size, until there was a fine line of sunlight around the edge of the moon.
Okay, now start the stopwatch!
But after the moon was completely inside the solar disk, the moon did look “smooth and circular” to him. At least four other local observers confirmed this observation during this eclipse.
Sunlight shining through lunar valleys
Later, others realized that these beads of light appeared due to mountains and valleys, crater walls, and other topographic features extending above the limb, or edge, of the moon as seen from Earth. This phenomenon earned the name Baily’s beads. And you can see it during total eclipses, too, just before the moon covers the sun completely. A video of Baily’s beads is here.
Baily published his discovery in the Monthly Notices of the Royal Astronomical Society in December of 1836. In a talk to the Royal Astronomical Society, he mentioned that he knew of only one other person who had seen these before, that being Jean Henri van Swinden (1746–1823), a Dutch scientist.
Today, Baily’s beads are one of the eclipse effects that amateur astronomers around the world – using proper eye protection – watch for during annular and total eclipses of the sun.
Francis Baily, for whom Baily’s beads are named. Image via Wikimedia Commons.
Baily’s beads during a total eclipse
Baily discovered the beads during an annular eclipse, but they’re best known for being visible during a total eclipse. Let’s look at the process during a total eclipse.
During a total eclipse, the moon moves across a sun that takes up the same amount of sky. As the leading edge of the moon moves toward covering the remainder of the sun, dark spots interrupt the last bit of sunlight. Those are lunar mountains. Totality has not yet begun, as sunlight is still peeking between these dark spots.
As the seconds tick by, the sunlight decreases, and the dark areas increase until there is only one spot of light on the limb of the moon: the diamond ring. When that final bright spot disappears, the total eclipse begins. Remove the solar filters for a fantastic view.
As the total phase draws to a close, the effects resume in reverse order. On the trailing side of the moon the sunlight appears. First, the diamond ring. Next, Baily’s beads. Watch a video of Baily’s beads during the August 21, 2017, total eclipse here.
The Baily’s beads phase is unappreciated during total eclipses. The main show is totality, and observers are typically preparing to remove their solar filters while Baily’s beads and the diamond ring are occurring. And those Baily’s beads at the end of totality? They are accompanied by sighs as the total phase comes to an abrupt end. But you can watch the phenomena at the end of the total eclipse with unfiltered and dark-adapted eyes, so they might appear brighter and more noteworthy than those leading into the total phase.
Baily’s beads, visible during a total eclipse of the sun. Here, you’re almost seeing another effect, known as the diamond ring. Image via Luc Viatour/ Encyclopedia Britannica.
Baily’s beads during an annular eclipse
Here is the process during an annular eclipse, the type that Baily saw. To start, the moon appears smaller than the sun, so you must use filters the entire time. At the center of the annular eclipse, you see a ring of the sun around the moon. And the episode begins on the trailing, not the leading, edge of the moon. As the last bit of the moon moves onto the sun, the uneven dark limb (edge) of the moon produces bright spots. These bright spots increase in number and size until the whole edge of the moon is a bright arc of sunlight.
That is what Baily saw. Toward the end of the annular phase of the eclipse, now looking toward the leading edge of the moon, that bright arc of sunlight begins to be interrupted by dark spots, growing in size. A video of Baily’s beads during an annular eclipse is here.
Extending the beads
Is there a way to make those beads visible for a longer length of time? Yes, there are two ways. One is to hop onto a jet and zoom along the path of the eclipse. This will also extend the length of the total phase of the eclipse.
The other way is to set up near the edge of the central path of the eclipse. The typical eclipse shows the main event, whether annular or total, only along a path on the earth that is about 100 miles (160 km) wide. Sit in the center of that path and the eclipse phase will last longer than near the north or south limit of this path. But if you go near the north or south limit, the Baily’s beads phase will last longer, at the sacrifice of the central phase. A video of Baily’s beads lasting more than two minutes is here.
Petr Horalek took these images from the La Silla Observatory in Chile during the July 2, 2019, total eclipse. He was near the edge of the path of totality. Image via Petr Horalek. Used by permission.
Baily’s beads or Halley’s beads?
On April 22, 1715 (Julian calendar, or May 3, 1715, Gregorian calendar) Edmond Halley (1656-1742) observed a total solar eclipse from London. He predicted the eclipse, and so it is often referred to as Halley’s Eclipse. During this total eclipse, Halley observed Baily’s beads too, 59 years before Baily was even born. Here is Halley’s description:
About two Minutes before the Total Immersion, the remaining part of the Sun was reduced to a very fine Horn, whose Extremeties seemed to lose their Acuteness, and to become round like Stars … which Appearance could proceed from no other Cause but the Inequalities of the Moon’s Surface, there being some elevated parts thereof near the Moon’s Southern Pole, by whose Interposition part of that exceedingly fine Filament of Light was intercepted.
This is an excellent description of Baily’s beads, even though Halley hit the “shift” key a few too many times!
Edmond Halley was the first to observe and identify the event we now call Baily’s beads, yet they are not named after him. What is named after Edmond Halley?
Halley’s Comet, which he did not discover, but he did predict its return. Halley’s Eclipse in 1715, which he also predicted. Halley, the crater on the moon, named long after Halley passed away. Halley, the crater on Mars, named in 1973. Halley Research Station, in Antarctica, established in 1956. Edmond Halley never went to Antarctica, nor to the moon nor Mars, for that matter. Halley’s Mount, a hill on the island of Saint Helena, from where Halley observed the southern sky.
But we don’t have “Halley’s beads,” even though he discovered and defined them. One suggestion is to refer to the beads seen during the annular eclipses as Baily’s beads and the ones seen during the total eclipses as Halley’s beads. Then Edmond Halley would finally be recognized for something he discovered.
Bottom line: May 15, 1836: Francis Baily, an English astronomer, saw light shining through lunar ridges during an eclipse of the sun. These are now known as Baily’s beads.
View at EarthSky Community Photos. | Kannan A in Woodlands, Singapore, captured this photo of the Southern Cross on March 8, 2021. He wrote: “The Southern Cross constellation seen here in the morning in Singapore looking south. On the left of this cross are the 2 pointer stars, Alpha Centauri (Rigel Kentaurus) and Beta Centauri (Hadar). They point to the Southern Cross.” Thanks, Kannan!
The Southern Cross – also known as Crux – is an iconic constellation for people south of the equator. It’s visible every clear night, and its stars shine brightly enough to be picked out pretty easily even from urban locations.
If you’re in the Northern Hemisphere, you might be able to see the famous Southern Cross too. You just need to be far enough south, and know where and when to look.
At 35 degrees south latitude and all latitudes farther south, you can see the Southern Cross all night, all year round. In that part of the Southern Hemisphere, the Southern Cross is circumpolar: it is always above the horizon, as it circles the sky close to the celestial pole.
However, for much of the Northern Hemisphere – including most of the United States – the Southern Cross can never be seen. It never rises above the horizon.
You can see all of Crux from the U.S. state of Hawaii. In the contiguous U.S., you must be in southern Florida or Texas (about 26 degrees north latitude or farther south). Even from the far-southern contiguous U.S., you have a limited viewing window for catching the Southern Cross. It must be the right season of the year. It must be the right time of night. And you have to look in the right direction: south!
For the Northern Hemisphere’s tropical and subtropical regions, May is a good time to find Crux in the evening sky. It is visible in other months, but not at such a convenient time. In March, you have to wait until about 1 a.m. to catch the Southern Cross at its highest elevation. In December and January, you have to catch it before dawn.
No matter the hour or date, Crux climbs to its highest point in the sky when it’s due south. It is easy to visualize the Cross, because it stands upright over the horizon.
View at EarthSky Community Photos. | Prateek Pandey in Bhopal, India, caught the Southern Cross while at its highest point around midnight (its midnight culmination) on March 6, 2021. In April and May, the Southern Cross reaches its highest point in the sky earlier in the evening. Thank you, Prateek!
Use the Big Dipper as a guide
Although the Big Dipper is a fixture of Northern Hemisphere skies, it has a close kinship with the Southern Cross. The Big Dipper and the Southern Cross are highest in the sky at the same time of year.
Remember, spring up and fall down: the Big Dipper soars highest in the sky during the Northern Hemisphere’s spring. When you see the Big Dipper above Polaris, the North Star, the Southern Cross can be seen standing over the southern horizon in Texas and southern Florida.
In the Southern Hemisphere it works the same way, just in reverse. You can see the Big Dipper in the Southern Hemisphere from about 26 degrees south latitude and all latitudes farther north. But to spot it, it depends on the season and the time of night. When the Southern Cross sails highest in the Southern Hemisphere sky, the “upside-down” Big Dipper is seen just above the northern horizon at latitudes near the tropic of Capricorn (23.5 degrees south latitude).
View at EarthSky Community Photos. | Dr Ski in Valencia, Philippines, captured the Southern Cross, along with its pointer stars, Alpha Centauri (far left) and Beta Centauri. He wrote: “When you see the Southern Cross for the first time, you understand now why you came this way. – CS&N.” Thanks, Dr Ski!
The Southern Cross in navigation
When European sailors journeyed south of the equator, they found that the North Star had disappeared below the horizon. As they sailed even farther south, the Big Dipper dropped out of sight as well. Unlike the Northern Hemisphere, the Southern Hemisphere has no bright pole star to highlight the celestial pole. Fortunately, the Southern Cross acts as a navigational aid.
View at EarthSky Community Photos. | Kannan A in Woodlands, Singapore, captured this photo of the Southern Cross on March 8, 2021. He wrote: “The Southern Cross constellation seen here in the morning in Singapore looking south. On the left of this cross are the 2 pointer stars, Alpha Centauri (Rigel Kentaurus) and Beta Centauri (Hadar). They point to the Southern Cross.” Thanks, Kannan!
The Southern Cross – also known as Crux – is an iconic constellation for people south of the equator. It’s visible every clear night, and its stars shine brightly enough to be picked out pretty easily even from urban locations.
If you’re in the Northern Hemisphere, you might be able to see the famous Southern Cross too. You just need to be far enough south, and know where and when to look.
At 35 degrees south latitude and all latitudes farther south, you can see the Southern Cross all night, all year round. In that part of the Southern Hemisphere, the Southern Cross is circumpolar: it is always above the horizon, as it circles the sky close to the celestial pole.
However, for much of the Northern Hemisphere – including most of the United States – the Southern Cross can never be seen. It never rises above the horizon.
You can see all of Crux from the U.S. state of Hawaii. In the contiguous U.S., you must be in southern Florida or Texas (about 26 degrees north latitude or farther south). Even from the far-southern contiguous U.S., you have a limited viewing window for catching the Southern Cross. It must be the right season of the year. It must be the right time of night. And you have to look in the right direction: south!
For the Northern Hemisphere’s tropical and subtropical regions, May is a good time to find Crux in the evening sky. It is visible in other months, but not at such a convenient time. In March, you have to wait until about 1 a.m. to catch the Southern Cross at its highest elevation. In December and January, you have to catch it before dawn.
No matter the hour or date, Crux climbs to its highest point in the sky when it’s due south. It is easy to visualize the Cross, because it stands upright over the horizon.
View at EarthSky Community Photos. | Prateek Pandey in Bhopal, India, caught the Southern Cross while at its highest point around midnight (its midnight culmination) on March 6, 2021. In April and May, the Southern Cross reaches its highest point in the sky earlier in the evening. Thank you, Prateek!
Use the Big Dipper as a guide
Although the Big Dipper is a fixture of Northern Hemisphere skies, it has a close kinship with the Southern Cross. The Big Dipper and the Southern Cross are highest in the sky at the same time of year.
Remember, spring up and fall down: the Big Dipper soars highest in the sky during the Northern Hemisphere’s spring. When you see the Big Dipper above Polaris, the North Star, the Southern Cross can be seen standing over the southern horizon in Texas and southern Florida.
In the Southern Hemisphere it works the same way, just in reverse. You can see the Big Dipper in the Southern Hemisphere from about 26 degrees south latitude and all latitudes farther north. But to spot it, it depends on the season and the time of night. When the Southern Cross sails highest in the Southern Hemisphere sky, the “upside-down” Big Dipper is seen just above the northern horizon at latitudes near the tropic of Capricorn (23.5 degrees south latitude).
View at EarthSky Community Photos. | Dr Ski in Valencia, Philippines, captured the Southern Cross, along with its pointer stars, Alpha Centauri (far left) and Beta Centauri. He wrote: “When you see the Southern Cross for the first time, you understand now why you came this way. – CS&N.” Thanks, Dr Ski!
The Southern Cross in navigation
When European sailors journeyed south of the equator, they found that the North Star had disappeared below the horizon. As they sailed even farther south, the Big Dipper dropped out of sight as well. Unlike the Northern Hemisphere, the Southern Hemisphere has no bright pole star to highlight the celestial pole. Fortunately, the Southern Cross acts as a navigational aid.
Skylab, America’s first space station, launched on May 14, 1973. Its highly publicized crash back to Earth – during which it dropped huge chunks of hardware into the Indian Ocean and across Western Australia – took place on July 11, 1979. Image via NASA.
On May 14, 1973, 53 years ago today, a Saturn V rocket launched Skylab – America’s 1st space station – into Earth-orbit. Three crews ultimately lived and worked on Skylab for over 171 days. However, the space station is perhaps best known for its dramatic and highly publicized fall back to Earth. Read more about that below.
Skylab used technology from the Apollo moon missions, including using the Apollo spacecraft to deliver the Skylab crews and return them to Earth.
Overall, Skylab had two important goals. First, NASA had set out to prove humans could work and live in space for extended periods of time. Second, the astronauts aboard Skylab would study and expand our knowledge of the sun and solar astronomy.
Pass me that book? Back on Skylab, they had no iPads for their information, but instead it was all pen and paper. #Skylab50pic.twitter.com/hed10WQTED
Upon liftoff, a meteoroid shield meant to shade the spacecraft deployed and tore itself off of the space station. So, the first crew had to remedy this situation while orbiting about 270 miles (435 km) above the surface of the Earth.
At the same time, the shade detachment caused one of the solar-array wings to partly deploy. Then, the 2nd stage retro-rockets blew it off into space. And because of this event, a strap from the shield covered another solar-array wing so that wing couldn’t open all the way to generate power.
Luckily, all the other equipment and spacecraft functions were fine. For example, the Apollo Telescope Mount – the solar observatory on Skylab – with its solar arrays, and most importantly, the pressurization of the space station, were all in good working order.
The Skylab team on Earth spent over a week working to stabilize Skylab and find workarounds for several issues. In addition, they addressed a serious overheating of the craft by varying its nose-up attitude to maintain an acceptable position.
Finally, the spacecraft was operational, but for some time functioned with less than 50% of its designed electrical system.
The Skylab 1-Saturn V space vehicle lifts off from Launch Pad 39A on May 14, 1973. Image via NASA.
Skylab was a success
Overall, there were three crews – with three members each – that lived on Skylab. They lived and worked on Skylab for a total of 171 days and 13 hours. The crews performed over 300 experiments, including testing human’s ability to live in zero gravity. They also observed the sun and Earth.
The crews set new space records that included man-hours in space and time in extravehicular activities. Their combined totals exceeded all the world’s previous spaceflights at that time.
Skylab showed humans could maintain a space station, perform experiments and remain in good physical health while living in the weightlessness of space. The 1st crew stayed onboard for 28 days. The 2nd crew were in space for 59 days. And the 3rd crew remained on the space station for 84 days. Also, Skylab was the first space station to receive resupply ships, now a common occurrence for the ISS.
The Skylab crew studied solar flares from space and tracked cyclones and hurricanes on Earth. Overall, they took more than 170,000 photos of the sun and over 46,000 photos of the Earth.
By the way, the 3rd crew made a few observations of comet Kohoutek, a comet that was hyped as a possible comet of the century but failed to live up to the hype.
As the crew leaves Skylab 2, they look back on a gold sun shield cover on the main portion of space station. The 4 windmill-like solar arrays are part of the Apollo Telescope Mount used for solar astronomy. Image via NASA.
The final days and fall of Skylab
After the last crew returned to Earth, the ground crew ran a few more tests of the systems onboard. Primarily they were checking for equipment failures and how much systems had degraded over the time spent in space.
Eventually, Skylab was moved in to position for reentry and all its systems were shut down. Its orbit was expected to decay over about 10 years.
But it only remained in a stable orbit for eight years and so came back to Earth earlier than expected.
And its fall to Earth was highly publicized! It was perhaps the first major fall of a satellite from orbit.
After much speculation about where Skylab would land – and whether it would damage people or things on the ground – Skylab finally crashed back to Earth on July 11, 1979. It caused big hunks of hardware to fall into the Indian Ocean and across Western Australia.
And, famously, it prompted the sparsely populated town of Esperance, in Western Australia, to fine NASA $400 for littering!
Bottom line: Skylab was America’s first space station. Three crews lived and worked in space for over 171 days. They studied the sun and Earth and demonstrated humans could live and work in space for long periods of time.
Skylab, America’s first space station, launched on May 14, 1973. Its highly publicized crash back to Earth – during which it dropped huge chunks of hardware into the Indian Ocean and across Western Australia – took place on July 11, 1979. Image via NASA.
On May 14, 1973, 53 years ago today, a Saturn V rocket launched Skylab – America’s 1st space station – into Earth-orbit. Three crews ultimately lived and worked on Skylab for over 171 days. However, the space station is perhaps best known for its dramatic and highly publicized fall back to Earth. Read more about that below.
Skylab used technology from the Apollo moon missions, including using the Apollo spacecraft to deliver the Skylab crews and return them to Earth.
Overall, Skylab had two important goals. First, NASA had set out to prove humans could work and live in space for extended periods of time. Second, the astronauts aboard Skylab would study and expand our knowledge of the sun and solar astronomy.
Pass me that book? Back on Skylab, they had no iPads for their information, but instead it was all pen and paper. #Skylab50pic.twitter.com/hed10WQTED
Upon liftoff, a meteoroid shield meant to shade the spacecraft deployed and tore itself off of the space station. So, the first crew had to remedy this situation while orbiting about 270 miles (435 km) above the surface of the Earth.
At the same time, the shade detachment caused one of the solar-array wings to partly deploy. Then, the 2nd stage retro-rockets blew it off into space. And because of this event, a strap from the shield covered another solar-array wing so that wing couldn’t open all the way to generate power.
Luckily, all the other equipment and spacecraft functions were fine. For example, the Apollo Telescope Mount – the solar observatory on Skylab – with its solar arrays, and most importantly, the pressurization of the space station, were all in good working order.
The Skylab team on Earth spent over a week working to stabilize Skylab and find workarounds for several issues. In addition, they addressed a serious overheating of the craft by varying its nose-up attitude to maintain an acceptable position.
Finally, the spacecraft was operational, but for some time functioned with less than 50% of its designed electrical system.
The Skylab 1-Saturn V space vehicle lifts off from Launch Pad 39A on May 14, 1973. Image via NASA.
Skylab was a success
Overall, there were three crews – with three members each – that lived on Skylab. They lived and worked on Skylab for a total of 171 days and 13 hours. The crews performed over 300 experiments, including testing human’s ability to live in zero gravity. They also observed the sun and Earth.
The crews set new space records that included man-hours in space and time in extravehicular activities. Their combined totals exceeded all the world’s previous spaceflights at that time.
Skylab showed humans could maintain a space station, perform experiments and remain in good physical health while living in the weightlessness of space. The 1st crew stayed onboard for 28 days. The 2nd crew were in space for 59 days. And the 3rd crew remained on the space station for 84 days. Also, Skylab was the first space station to receive resupply ships, now a common occurrence for the ISS.
The Skylab crew studied solar flares from space and tracked cyclones and hurricanes on Earth. Overall, they took more than 170,000 photos of the sun and over 46,000 photos of the Earth.
By the way, the 3rd crew made a few observations of comet Kohoutek, a comet that was hyped as a possible comet of the century but failed to live up to the hype.
As the crew leaves Skylab 2, they look back on a gold sun shield cover on the main portion of space station. The 4 windmill-like solar arrays are part of the Apollo Telescope Mount used for solar astronomy. Image via NASA.
The final days and fall of Skylab
After the last crew returned to Earth, the ground crew ran a few more tests of the systems onboard. Primarily they were checking for equipment failures and how much systems had degraded over the time spent in space.
Eventually, Skylab was moved in to position for reentry and all its systems were shut down. Its orbit was expected to decay over about 10 years.
But it only remained in a stable orbit for eight years and so came back to Earth earlier than expected.
And its fall to Earth was highly publicized! It was perhaps the first major fall of a satellite from orbit.
After much speculation about where Skylab would land – and whether it would damage people or things on the ground – Skylab finally crashed back to Earth on July 11, 1979. It caused big hunks of hardware to fall into the Indian Ocean and across Western Australia.
And, famously, it prompted the sparsely populated town of Esperance, in Western Australia, to fine NASA $400 for littering!
Bottom line: Skylab was America’s first space station. Three crews lived and worked in space for over 171 days. They studied the sun and Earth and demonstrated humans could live and work in space for long periods of time.
A great Tyrannosaurus rex strides through the conifer trees of her territory, sniffing the air. She picks up the scent from the carcass of a dead horned dinosaur, Triceratops, that she was feeding on yesterday. She walks over and strips off some more shreds of meat, but the smell is foul even for her.
So she goes down to the lake to drink and small crocodiles and turtles scuttle into the water. But she hardly sees them. Of more interest is an armored dinosaur, Ankylosaurus, lurking nearby. However, she knows this dinosaur won’t be an easy kill and she isn’t desperate enough for food to risk a fight. Little does she know there are bigger dangers ahead. She looks up and sees a bright light racing downwards accompanied by faint crackling and sizzling noises.
Our T. rex has excellent hearing for low frequency sounds. And she is disturbed by the vibrations she can feel. But her upset only lasts for a moment. In a flash, she has been burnt to a crisp and her world changed forever.
Would you have survived when the asteroid killed the dinosaurs?
This all happened 66 million years ago, when a huge asteroid famously hit Earth in the area of what is now the Caribbean. At the end of the Cretaceous period, sea levels were 100–200 meters (330–660 feet) higher than today, so the shores of the Caribbean lay far inland over eastern Mexico and the southern United States. The impact happened entirely within these waters.
The event triggered instant changes to our planet and its atmosphere. And it led to the extinction of the dinosaurs and about half Earth’s other species. But what would it have been like to experience such a gargantuan impact? What would you have seen, heard or smelled? And how would you have died … or survived?
As experts on meteoritics and paleontology, respectively, we’ve created a detailed timeline, based on decades of research, to take you right there. So let’s start by traveling back in time to the very last day of the Cretaceous.
Here’s how University of Manchester Science and Engineering envisioned the dino-killing asteroid.
T-minus 1 day
All is calm and the Cretaceous day proceeds as usual. In what will soon be ground zero, it is pleasantly warm, about 26°C (79°F), and wet. It often is. For about a week, the asteroid has been visible only at night. Because the giant rock is heading straight towards Earth, it looks like a motionless star. There is no dramatic tail; this is a rocky asteroid rather than a comet.
In the last 24 hours, the light becomes visible during the daytime. But it still looks like a star or planet, getting brighter in the final few hours before impact.
T equals 0: The impact
If you were close by, you would first have experienced a brief light and sound show. Minutes to seconds before the impact, you’d have seen the bright fireball, and its accompanying crackling or fizzing noises. This sizzling sound is a result of the photo-acoustic effect: the intense light of the fireball warms the ground. Then that, in turn, heats the air above it, causing pressure waves, or sound.
Next is a deafening sonic boom. It occurs because the asteroid is traveling faster than the speed of sound. But the asteroid is so huge, perhaps 10 km (6 miles) in diameter, that it almost certainly hits the ground before any living creature near the impact zone has time to run for cover.
The asteroid’s enormous energy forms a crater through a series of processes that together take only a few seconds. As the asteroid collides with the surface, its kinetic (movement) energy is instantly transferred to the surface as a combination of kinetic, thermal (heat) and seismic energy (released during earthquakes). This results in a series of shock waves that heat and compress both the asteroid and its target.
As the shock waves propagate, rocks fracture, break up and are ejected. This produces a bowl-shaped depression, or transient cavity, about 10 seconds after impact. The heat and compression also melt and vaporize large volumes of material, including the asteroid itself, releasing a fountain of incandescent vapor (its temperature is more than 10,000 K, or 9,700°C, or 17,500°F).
Over the next few seconds, the cavity increases in size to many times the diameter of the original asteroid. Simulations suggest that around 20 seconds after impact, the transient cavity is at least 30 km (19 miles) deep. That’s deeper than the deepest depth currently known on Earth, the 11 km (7 miles) Challenger Deep valley, part of the Pacific Ocean’s Marianas Trench. The rim of the crater is over 20 km (12.5 miles) high, more than twice the height of 8,900-meter (29,200 feet) Mount Everest.
But this enormous feature lasts for less than a minute before it starts to collapse. Within three minutes of the impact, the center of the crater has rebounded to form a peak several kilometers high. The peak only lasts about two minutes before collapsing back into the crater.
Whether a dinosaur or a dung beetle, if you were near the transient cavity, you would have been incinerated instantly by the blast. But even if you were up to 2,000 km (1,250 miles) from the epicenter, you’d likely have been killed quickly by the thermal radiation and supersonic winds now spreading out from the impact site.
T-plus 5 minutes
Five minutes after the impact, the winds have “eased” to those of a category 5 hurricane, flattening everything within about 1,500 km (930 miles) of the impact. Destroying everything, that is, which has not already been burnt. Atmospheric temperatures in the region rise to over 500K (226.85°C). This would feel like being inside an oven, causing burns, heatstroke and death. Wood and plant matter ignite, creating fires everywhere.
Because the asteroid struck the sea, the atmosphere is also filled with super-heated steam, making the hurricane-force winds even deadlier.
Next come the tidal waves, triggered by the vast quantities of displaced rock and water. These 100-meter megatsunamis first strike the shores of what is now the Gulf of Mexico. They engulf the land before depositing huge amounts of debris as they retreat.
By now, the crater has almost reached its final dimensions: 180 km across and 20 km deep. But making an enormous hole in the ground isn’t the only outcome of the impact. All the rock and vapor displaced during the collision has to go somewhere. Several locations in North America show that meter-sized blocks of debris from the impact were thrown distances of hundreds of kilometers.
So if you were 2,000 to 3,000 km from the epicenter and survived the first few seconds, you’d most likely die from overheating, earthquakes, hurricanes, fires, tsunami-driven floods or being hit by impact melt.
But what is happening much further away? In the first five minutes after impact, dinosaurs roaming the Cretaceous forests of what are now China or New Zealand are so far undisturbed.
But it won’t be long before that changes.
T-plus 1 hour
Shockwaves on land and sea are only minor inconveniences compared with the fire that is still radiating down from the sky. Some of the impact energy has been transferred into the atmosphere, heating the air and dust to incandescence.
An hour after impact, a belt of dust has circled the globe. Deposits of solidified molten droplets (impact spherules) and mineral grains have been found in numerous locations from New Zealand in the south to Denmark in the north. In these locations, you would not have been aware of the tsunamis around the Americas or the wildfires, but the skies would certainly have begun to darken.
T-plus 1 day
By now, huge tsunamis are moving east across the Atlantic and west across the Pacific, entering the Indian Ocean from both sides.
They are still around 50 meters (165 feet) high. They cause death and destruction across many coasts around the world. By comparison, the 2004 Boxing Day tsunami reached heights of up to 30 meters. Tsunamis kill fishes and marine life that are washed high on the shore and then dumped, just as they kill coastal trees and drown land animals. But the tsunamis gradually fade away and probably don’t wipe out any entire species … at least on their own.
The hurricane-force winds have also died down. But tropical storm strength winds are whipping up debris and causing further chaos and destruction across the tsunami-affected areas. The burning sky is also triggering wildfires across the globe. And these, in turn, carry ever more soot into the atmosphere. The sooty signature of these wildfires has been found deposited as carbon particles in sediments from the K-Pg boundary, a 66-million-year-old thin clay layer.
Further away, in what is modern Europe and Asia, the skies continue to fill up with dust and soot, as they do everywhere. Temperatures start to drop as sunlight is blocked. Trees and plants in general, including phytoplankton, close down as if for winter, unable to photosynthesize. Any animals that rely on warm conditions ultimately hunker down and die.
T-plus 1 week
It’s getting darker and darker. Simulations of solar radiation reaching the Earth’s surface following the impact indicate that, after about a week, the solar flux (the amount of heat and light per a certain area) is just one thousandth of that prior to the impact. This is caused by particles of dust and soot in the atmosphere.
The continued decrease in light levels is accompanied by a global drop in surface temperatures of at least 5° C (9 F). This means that most of the dinosaurs and other large flying and swimming reptiles probably die from freezing within the course of this first week. (Smaller reptiles with slower metabolisms or more flexible diets could survive longer.) Cooling temperatures and cloud cover also lead to rain. But not just any rain. Storms of acid rain fall across Earth.
Two separate mechanisms generate acid rain. The first is down to the geology of the impact region. The asteroid happened to hit an area of sediments rich in sulfur. These vaporized and caused sulfur oxides (acidic and pungent gas compounds composed of sulfur and oxygen) to be part of the plume of plasma blasted into the atmosphere. Second, the energy of the collision was sufficient to turn nitrogen and oxygen into nitrogen oxides, highly reactive gases that can form smog.
The dropping temperature ultimately allows water vapor to condense into drops. And the sulfur and nitrogen oxides dissolve to form sulfuric and nitric acids. This is sufficient to generate a rapid drop in pH. Early models suggest that the pH of the rain might be as low as 1: the same acidity as battery acid.
At this point, Earth is not a great place to be. Rotting vegetation, choking smoke and sulfur aerosols combine to make the planet stink. Plants and animals on land and in shallow seas that have survived the darkness and cold succumb to the corrosive acid rain and ocean acidification. Acid rain also kills trees by leaching nutrients such as calcium, magnesium and potassium from the soil. Shallow marine shellfish, crustaceans and corals also die as acid seawater destroys their skeletons.
T-plus 1 year
Winds die down, wildfires are extinguished and the oceans are once again calm. It might appear that the asteroid collision is just a scar on the ocean floor. But its effects are still destructive. The atmosphere is still filled with dust. And the sun hasn’t shone for a year. Temperatures have continued to drop, with the average surface temperature now 15° C (27 F) lower than before the impact. Winter has come.
Any dinosaurs or marine reptiles that survived the first week of freezing conditions would have died very soon after. A year after the impact, only rotted skeletons of these behemoths remain. Here and there, smaller animals like mammals the size of rats and insects would be nestling in crevices, barely surviving on their reserves and decaying plants.
While most plant groups and many of the modern groups of insects, fishes, reptiles, birds and mammals recover reasonably rapidly, things don’t look great for other species. Dinosaurs and pterosaurs living on land are extinct, as are many marine reptiles, ammonites, belemnites and rudist bivalves in the oceans. Ammonites and belemnites are high in their food chains, and so suffer not only from the cold and acidification but also from the loss of abundant food resources, such as smaller marine organisms.
T-plus 10 years
Earth is still in the grip of a fierce winter. Although most of the sulfur has rained out of the atmosphere, dust and soot particles remain. The average surface temperature is still about 5° C lower than before the impact. The main oceans have not frozen, but inland lakes and rivers around the world are iced over.
Clearly, there were no humans about at this time. There weren’t even any larger mammals. But given the only species that survived were those that could burrow or live below water, it is unlikely that you could have survived this long.
Surviving plant and animal groups such as turtles, smaller crocodiles, lizards, snakes, some ground-dwelling birds and small mammals repopulate the Earth at this point. But they are forced back to limited areas of relative safety a long way from the impact site. These areas are now receiving sufficient sunlight for plants and phytoplankton to photosynthesize again. As leaves and seeds provide the basis for the food chains on land and in the sea, life begins to rebuild.
Eventually, life returns to the devastated landscapes. But ecosystems are very different and the dinosaurs are no more.
T-plus 66 million years
Today, 66 million years after the impact, the scars of the collision are hidden within geological strata. And scientists have started deciphering them. It was in 1980 that researchers first reported evidence of the impact. In their classic paper, Luis Alvarez, a Nobel-prize-winning physicist, and co-authors described a sudden enrichment in the element iridium in a specific clay layer in Denmark and in Italy.
Iridium is rare in surface rocks because most of it was sequestered in Earth’s core when the planet first formed. However, iridium is in meteorites. Alvarez and colleagues inferred that the rate of accumulation of the metal in the sediments was so high that it could only have been produced by impact of a gigantic meteorite.
Because the scientists had only observed the iridium spike in two locations, many scientists rejected the impact hypothesis at the time. However, through the 1980s, people identified iridium spikes in clay layers at more and more locations … in muds laid down on land, in lakes, in the sea.
Support for an impact hypothesis strengthened when scientists found a crater of the correct age in 1991. The crater is buried beneath younger rocks. But it’s clearly visible in geophysical surveys, lying half on land in the Yucatán Peninsula of Mexico, and half offshore. Since 1990, evidence for the impact has increased, not least when scientists discovered there was indeed a sharp cooling event at the end of the Cretaceous.
Possible T rex footprint from New Mexico. Image via Wikipedia, CC BY-SA.
The result of when the asteroid killed the dinos
In total, some half the species of plants and animals alive at the end of the Cretaceous disappeared. It was once thought that surviving groups such as many plants, insects, mollusks, lizards, birds and mammals somehow escaped unscathed. But detailed study shows that this is not the case: They were all hit hard.
But, by chance or luck, enough individuals and species were able to survive the cold and absence of food, or were in parts of the world where the effects were less extreme. As the world returned to normal, they had the opportunity to expand rapidly into their old niches, but also to occupy the space vacated by extinct groups. In fact, one important consequence of the extinction of the dinosaurs, apex predators in their heyday, was the successful spread and evolution of mammals.
When Alvarez and colleagues first described the drop in temperature following the impact, they called it a “nuclear winter”, reflecting the political climate of the early 1980s. Now we might be more inclined to describe the effects as a global climate change. Similar events are currently resulting from increased carbon dioxide in the atmosphere (flooding, temperature fluctuations).
It is salutary to think that without the asteroid collision, primates might never have reached the level we are at today. But it is equally salutary to consider that modern humans are causing some of the same changes to the atmosphere that ultimately killed our reptilian forbears and may one day also lead to our own demise.
Bottom line: What happened when the asteroid killed the dinosaurs some 66 million years ago? Read a blow-by-blow account of what the dinosaurs underwent.
A great Tyrannosaurus rex strides through the conifer trees of her territory, sniffing the air. She picks up the scent from the carcass of a dead horned dinosaur, Triceratops, that she was feeding on yesterday. She walks over and strips off some more shreds of meat, but the smell is foul even for her.
So she goes down to the lake to drink and small crocodiles and turtles scuttle into the water. But she hardly sees them. Of more interest is an armored dinosaur, Ankylosaurus, lurking nearby. However, she knows this dinosaur won’t be an easy kill and she isn’t desperate enough for food to risk a fight. Little does she know there are bigger dangers ahead. She looks up and sees a bright light racing downwards accompanied by faint crackling and sizzling noises.
Our T. rex has excellent hearing for low frequency sounds. And she is disturbed by the vibrations she can feel. But her upset only lasts for a moment. In a flash, she has been burnt to a crisp and her world changed forever.
Would you have survived when the asteroid killed the dinosaurs?
This all happened 66 million years ago, when a huge asteroid famously hit Earth in the area of what is now the Caribbean. At the end of the Cretaceous period, sea levels were 100–200 meters (330–660 feet) higher than today, so the shores of the Caribbean lay far inland over eastern Mexico and the southern United States. The impact happened entirely within these waters.
The event triggered instant changes to our planet and its atmosphere. And it led to the extinction of the dinosaurs and about half Earth’s other species. But what would it have been like to experience such a gargantuan impact? What would you have seen, heard or smelled? And how would you have died … or survived?
As experts on meteoritics and paleontology, respectively, we’ve created a detailed timeline, based on decades of research, to take you right there. So let’s start by traveling back in time to the very last day of the Cretaceous.
Here’s how University of Manchester Science and Engineering envisioned the dino-killing asteroid.
T-minus 1 day
All is calm and the Cretaceous day proceeds as usual. In what will soon be ground zero, it is pleasantly warm, about 26°C (79°F), and wet. It often is. For about a week, the asteroid has been visible only at night. Because the giant rock is heading straight towards Earth, it looks like a motionless star. There is no dramatic tail; this is a rocky asteroid rather than a comet.
In the last 24 hours, the light becomes visible during the daytime. But it still looks like a star or planet, getting brighter in the final few hours before impact.
T equals 0: The impact
If you were close by, you would first have experienced a brief light and sound show. Minutes to seconds before the impact, you’d have seen the bright fireball, and its accompanying crackling or fizzing noises. This sizzling sound is a result of the photo-acoustic effect: the intense light of the fireball warms the ground. Then that, in turn, heats the air above it, causing pressure waves, or sound.
Next is a deafening sonic boom. It occurs because the asteroid is traveling faster than the speed of sound. But the asteroid is so huge, perhaps 10 km (6 miles) in diameter, that it almost certainly hits the ground before any living creature near the impact zone has time to run for cover.
The asteroid’s enormous energy forms a crater through a series of processes that together take only a few seconds. As the asteroid collides with the surface, its kinetic (movement) energy is instantly transferred to the surface as a combination of kinetic, thermal (heat) and seismic energy (released during earthquakes). This results in a series of shock waves that heat and compress both the asteroid and its target.
As the shock waves propagate, rocks fracture, break up and are ejected. This produces a bowl-shaped depression, or transient cavity, about 10 seconds after impact. The heat and compression also melt and vaporize large volumes of material, including the asteroid itself, releasing a fountain of incandescent vapor (its temperature is more than 10,000 K, or 9,700°C, or 17,500°F).
Over the next few seconds, the cavity increases in size to many times the diameter of the original asteroid. Simulations suggest that around 20 seconds after impact, the transient cavity is at least 30 km (19 miles) deep. That’s deeper than the deepest depth currently known on Earth, the 11 km (7 miles) Challenger Deep valley, part of the Pacific Ocean’s Marianas Trench. The rim of the crater is over 20 km (12.5 miles) high, more than twice the height of 8,900-meter (29,200 feet) Mount Everest.
But this enormous feature lasts for less than a minute before it starts to collapse. Within three minutes of the impact, the center of the crater has rebounded to form a peak several kilometers high. The peak only lasts about two minutes before collapsing back into the crater.
Whether a dinosaur or a dung beetle, if you were near the transient cavity, you would have been incinerated instantly by the blast. But even if you were up to 2,000 km (1,250 miles) from the epicenter, you’d likely have been killed quickly by the thermal radiation and supersonic winds now spreading out from the impact site.
T-plus 5 minutes
Five minutes after the impact, the winds have “eased” to those of a category 5 hurricane, flattening everything within about 1,500 km (930 miles) of the impact. Destroying everything, that is, which has not already been burnt. Atmospheric temperatures in the region rise to over 500K (226.85°C). This would feel like being inside an oven, causing burns, heatstroke and death. Wood and plant matter ignite, creating fires everywhere.
Because the asteroid struck the sea, the atmosphere is also filled with super-heated steam, making the hurricane-force winds even deadlier.
Next come the tidal waves, triggered by the vast quantities of displaced rock and water. These 100-meter megatsunamis first strike the shores of what is now the Gulf of Mexico. They engulf the land before depositing huge amounts of debris as they retreat.
By now, the crater has almost reached its final dimensions: 180 km across and 20 km deep. But making an enormous hole in the ground isn’t the only outcome of the impact. All the rock and vapor displaced during the collision has to go somewhere. Several locations in North America show that meter-sized blocks of debris from the impact were thrown distances of hundreds of kilometers.
So if you were 2,000 to 3,000 km from the epicenter and survived the first few seconds, you’d most likely die from overheating, earthquakes, hurricanes, fires, tsunami-driven floods or being hit by impact melt.
But what is happening much further away? In the first five minutes after impact, dinosaurs roaming the Cretaceous forests of what are now China or New Zealand are so far undisturbed.
But it won’t be long before that changes.
T-plus 1 hour
Shockwaves on land and sea are only minor inconveniences compared with the fire that is still radiating down from the sky. Some of the impact energy has been transferred into the atmosphere, heating the air and dust to incandescence.
An hour after impact, a belt of dust has circled the globe. Deposits of solidified molten droplets (impact spherules) and mineral grains have been found in numerous locations from New Zealand in the south to Denmark in the north. In these locations, you would not have been aware of the tsunamis around the Americas or the wildfires, but the skies would certainly have begun to darken.
T-plus 1 day
By now, huge tsunamis are moving east across the Atlantic and west across the Pacific, entering the Indian Ocean from both sides.
They are still around 50 meters (165 feet) high. They cause death and destruction across many coasts around the world. By comparison, the 2004 Boxing Day tsunami reached heights of up to 30 meters. Tsunamis kill fishes and marine life that are washed high on the shore and then dumped, just as they kill coastal trees and drown land animals. But the tsunamis gradually fade away and probably don’t wipe out any entire species … at least on their own.
The hurricane-force winds have also died down. But tropical storm strength winds are whipping up debris and causing further chaos and destruction across the tsunami-affected areas. The burning sky is also triggering wildfires across the globe. And these, in turn, carry ever more soot into the atmosphere. The sooty signature of these wildfires has been found deposited as carbon particles in sediments from the K-Pg boundary, a 66-million-year-old thin clay layer.
Further away, in what is modern Europe and Asia, the skies continue to fill up with dust and soot, as they do everywhere. Temperatures start to drop as sunlight is blocked. Trees and plants in general, including phytoplankton, close down as if for winter, unable to photosynthesize. Any animals that rely on warm conditions ultimately hunker down and die.
T-plus 1 week
It’s getting darker and darker. Simulations of solar radiation reaching the Earth’s surface following the impact indicate that, after about a week, the solar flux (the amount of heat and light per a certain area) is just one thousandth of that prior to the impact. This is caused by particles of dust and soot in the atmosphere.
The continued decrease in light levels is accompanied by a global drop in surface temperatures of at least 5° C (9 F). This means that most of the dinosaurs and other large flying and swimming reptiles probably die from freezing within the course of this first week. (Smaller reptiles with slower metabolisms or more flexible diets could survive longer.) Cooling temperatures and cloud cover also lead to rain. But not just any rain. Storms of acid rain fall across Earth.
Two separate mechanisms generate acid rain. The first is down to the geology of the impact region. The asteroid happened to hit an area of sediments rich in sulfur. These vaporized and caused sulfur oxides (acidic and pungent gas compounds composed of sulfur and oxygen) to be part of the plume of plasma blasted into the atmosphere. Second, the energy of the collision was sufficient to turn nitrogen and oxygen into nitrogen oxides, highly reactive gases that can form smog.
The dropping temperature ultimately allows water vapor to condense into drops. And the sulfur and nitrogen oxides dissolve to form sulfuric and nitric acids. This is sufficient to generate a rapid drop in pH. Early models suggest that the pH of the rain might be as low as 1: the same acidity as battery acid.
At this point, Earth is not a great place to be. Rotting vegetation, choking smoke and sulfur aerosols combine to make the planet stink. Plants and animals on land and in shallow seas that have survived the darkness and cold succumb to the corrosive acid rain and ocean acidification. Acid rain also kills trees by leaching nutrients such as calcium, magnesium and potassium from the soil. Shallow marine shellfish, crustaceans and corals also die as acid seawater destroys their skeletons.
T-plus 1 year
Winds die down, wildfires are extinguished and the oceans are once again calm. It might appear that the asteroid collision is just a scar on the ocean floor. But its effects are still destructive. The atmosphere is still filled with dust. And the sun hasn’t shone for a year. Temperatures have continued to drop, with the average surface temperature now 15° C (27 F) lower than before the impact. Winter has come.
Any dinosaurs or marine reptiles that survived the first week of freezing conditions would have died very soon after. A year after the impact, only rotted skeletons of these behemoths remain. Here and there, smaller animals like mammals the size of rats and insects would be nestling in crevices, barely surviving on their reserves and decaying plants.
While most plant groups and many of the modern groups of insects, fishes, reptiles, birds and mammals recover reasonably rapidly, things don’t look great for other species. Dinosaurs and pterosaurs living on land are extinct, as are many marine reptiles, ammonites, belemnites and rudist bivalves in the oceans. Ammonites and belemnites are high in their food chains, and so suffer not only from the cold and acidification but also from the loss of abundant food resources, such as smaller marine organisms.
T-plus 10 years
Earth is still in the grip of a fierce winter. Although most of the sulfur has rained out of the atmosphere, dust and soot particles remain. The average surface temperature is still about 5° C lower than before the impact. The main oceans have not frozen, but inland lakes and rivers around the world are iced over.
Clearly, there were no humans about at this time. There weren’t even any larger mammals. But given the only species that survived were those that could burrow or live below water, it is unlikely that you could have survived this long.
Surviving plant and animal groups such as turtles, smaller crocodiles, lizards, snakes, some ground-dwelling birds and small mammals repopulate the Earth at this point. But they are forced back to limited areas of relative safety a long way from the impact site. These areas are now receiving sufficient sunlight for plants and phytoplankton to photosynthesize again. As leaves and seeds provide the basis for the food chains on land and in the sea, life begins to rebuild.
Eventually, life returns to the devastated landscapes. But ecosystems are very different and the dinosaurs are no more.
T-plus 66 million years
Today, 66 million years after the impact, the scars of the collision are hidden within geological strata. And scientists have started deciphering them. It was in 1980 that researchers first reported evidence of the impact. In their classic paper, Luis Alvarez, a Nobel-prize-winning physicist, and co-authors described a sudden enrichment in the element iridium in a specific clay layer in Denmark and in Italy.
Iridium is rare in surface rocks because most of it was sequestered in Earth’s core when the planet first formed. However, iridium is in meteorites. Alvarez and colleagues inferred that the rate of accumulation of the metal in the sediments was so high that it could only have been produced by impact of a gigantic meteorite.
Because the scientists had only observed the iridium spike in two locations, many scientists rejected the impact hypothesis at the time. However, through the 1980s, people identified iridium spikes in clay layers at more and more locations … in muds laid down on land, in lakes, in the sea.
Support for an impact hypothesis strengthened when scientists found a crater of the correct age in 1991. The crater is buried beneath younger rocks. But it’s clearly visible in geophysical surveys, lying half on land in the Yucatán Peninsula of Mexico, and half offshore. Since 1990, evidence for the impact has increased, not least when scientists discovered there was indeed a sharp cooling event at the end of the Cretaceous.
Possible T rex footprint from New Mexico. Image via Wikipedia, CC BY-SA.
The result of when the asteroid killed the dinos
In total, some half the species of plants and animals alive at the end of the Cretaceous disappeared. It was once thought that surviving groups such as many plants, insects, mollusks, lizards, birds and mammals somehow escaped unscathed. But detailed study shows that this is not the case: They were all hit hard.
But, by chance or luck, enough individuals and species were able to survive the cold and absence of food, or were in parts of the world where the effects were less extreme. As the world returned to normal, they had the opportunity to expand rapidly into their old niches, but also to occupy the space vacated by extinct groups. In fact, one important consequence of the extinction of the dinosaurs, apex predators in their heyday, was the successful spread and evolution of mammals.
When Alvarez and colleagues first described the drop in temperature following the impact, they called it a “nuclear winter”, reflecting the political climate of the early 1980s. Now we might be more inclined to describe the effects as a global climate change. Similar events are currently resulting from increased carbon dioxide in the atmosphere (flooding, temperature fluctuations).
It is salutary to think that without the asteroid collision, primates might never have reached the level we are at today. But it is equally salutary to consider that modern humans are causing some of the same changes to the atmosphere that ultimately killed our reptilian forbears and may one day also lead to our own demise.
Bottom line: What happened when the asteroid killed the dinosaurs some 66 million years ago? Read a blow-by-blow account of what the dinosaurs underwent.
This illustration shows 2 black holes spiraling toward a colossal collision. A new study says mergers like this could explain how mysteriously large black holes form. Image via LIGO/ Caltech/ Simulating eXtreme Spacetimes Collaboration.
Over the past decade, astronomers have detected many black holes that seem too massive to have formed from the collapse of a single star. So how did they form?
Researchers have just found new evidence that these black holes form from chaotic collisions between multiple smaller black holes.
The finding comes from studying ripples in the fabric of spacetime that these black holes send out into the universe.
A new study has provided fresh evidence that some of the largest stellar-mass black holes didn’t form directly from the collapse of massive stars. Instead, the research suggests, they were built from chaotic collisions and repeated mergers between multiple smaller black holes.
Stellar-mass black holes are black holes ranging from a few times the mass of our sun to tens of solar masses. And on May 7, 2026, the researchers said they’ve identified two distinct populations of these black holes.
The first population, those less than 45 times the mass of our sun, formed as we’d typically expect: from stars collapsing at the end of their lives. But the second population – those over 45 solar masses – is more mysterious. Astronomers have long suspected that these are too massive to have formed from the collapse of single stars. And the new research helps explain how they’ve come to exist.
The scientists noticed that these larger black holes are spinning faster and in much more varied directions than the smaller ones. They say this is evidence that the larger black holes are the product of black hole collisions in the maelstrom of dense star clusters.
They performed this study using new data from gravitational waves observations. The research team analyzed data from a catalog of observations, called the LIGO–Virgo–KAGRA Gravitational-Wave Transient Catalog version 4 (GWTC4). In it, they found 153 detections of black hole mergers.
Gravitational wave astronomy is now doing more than counting black hole mergers. It is starting to reveal how black holes grow, where they grow, and what that tells us about the lives and deaths of massive stars. This is exciting because we can use the information to test our understanding of how stars and [star] clusters evolve in the universe.
The team published its findings in the peer-reviewed journal Nature Astronomy on May 7, 2026.
Detecting ripples in spacetime
A black hole first forms when a massive star runs out of fuel for nuclear fusion. As a result, it collapses under its own gravity. The star’s mass becomes so compact that nothing can escape its powerful gravitational force … not even light.
In dense star clusters, two black holes often get close enough to start orbiting each other. As the two objects rotate, they generate a unique pattern of gravitational waves, or ripples in the fabric of the universe. The wave characteristics depend on the mass of each object, as well as their distance and orbit orientation from Earth.
This computer simulation shows the merger of 2 black holes. As the black holes spiral toward each other, collide and merge, they create gravitational waves. Scientists made this simulation using equations from Albert Einstein’s theory of general relativity and data from the Laser Interferometer Gravitational-wave Observatory (LIGO). Video via the Simulating eXtreme Spacetimes (SXS) project.
The orbiting black hole pair radiates gravitational waves, resulting in some loss of orbital energy. As a result, the black holes get closer. That causes them to orbit each other faster, which radiates even stronger gravitational waves, which makes them get closer, and so on. The final outcome is a violent merger of the two objects.
Gravitational wave laser interferometers are able to detect the final orbits of the black holes just before the merger, which occurs over a timeframe of seconds.
Two populations of black holes
The scientists analyzed 153 black hole mergers in the LIGO–Virgo–KAGRA’s Gravitational-Wave Transient Catalog version 4. This catalog is a compilation of all gravitational wave detections from May 2023 to January 2024.
They noticed two distinct populations of stellar black holes. Isobel Romero-Shaw, also of Cardiff University, said:
What surprised us most was how clearly the high mass black holes [over 45 solar masses] stand out as a separate population.
Unlike the lower mass systems we analyzed, which were generally slowly-spinning, the higher mass systems are consistent with having more rapid spins, oriented in seemingly random directions. This is the exact signature you would expect if black holes were repeatedly merging in dense star clusters.
Messier 80 is a dense globular star cluster, about 28,000 light-years away, in the constellation Scorpius the Scorpion. The new study suggests that huge stellar-mass black holes form via chaotic collisions between multiple smaller black holes in dense star clusters like this. Image via NASA, ESA, G. Piotto, and G. Kober.
The pair-instability mass gap
There’s a theory in stellar evolution called the pair-instability mass gap. It states that stars above a certain mass limit will violently explode, rather than becoming a black hole. In their study, the team established that this limit was 45 solar masses. Therefore, any star over that value would explode at the end of its lifetime.
According to this theory, a collapsing star wouldn’t be able to form a black hole over 45 solar masses. However, gravitational wave detections have shown that stellar-mass black holes over this threshold do indeed exist.
Antonini said:
In our study we find evidence for the long-predicted pair-instability mass gap — a range of masses where stars are not expected to leave behind black holes at all. Gravitational wave detectors have successfully found black holes that appear to sit in or near that gap, which we identify at around 45 solar masses.
So how did these huge black holes form? The answer, Antonini says, lies in their spin:
The biggest black holes in the current sample seem to be telling us about [star] cluster dynamics, not just stellar evolution. Above about 45 solar masses the [black hole] spin distribution changes in a way that is hard to explain with normal stellar binaries alone but is naturally explained if these black holes have already been through earlier mergers in dense [star] clusters.
So the smaller black holes have similar spins, having formed from a population of similar stars. But when the black holes cross this 45-solar-mass line, they start to show a wide range of different spin speeds and orientations. The researchers think this erratic spinning is a sign that the large black holes have been through a series of violent collisions and mergers.
How gravitational wave laser interferometers work
If you threw two stones into a pond, each stone creates concentric ripples. The sections where the ripples intersect are called interference patterns. Gravitational wave laser interferometers look for laser beam interference patterns caused by gravitational waves.
A gravitational wave observatory has two long, perpendicular arms. For instance, at the LIGO observatories in Washington and Louisiana, each arm is 2.5 miles (4 km) long. A laser beam is split to shine along each arm. At the end of the arm, a mirror reflects the beam back and the two beams meet to form an interference pattern.
When gravitational waves pass through, spacetime itself oscillates. As a result, each wave stretches one arm and compresses the other. Therefore, the lasers move through slightly different lengths. The resulting interference patterns reveal information about the objects that generated the gravitational waves. This instrument is so sensitive that it can detect an arm length difference that’s 1/10,000th the width of a proton.
A brief animation showing the basic operation of the LIGO interferometer. Video via LIGO/ Einstein’s Messengers/ NSF.
Besides LIGO, there are two other gravitational wave observatories: the Virgo interferometer in Italy and the Kamioka Gravitational Wave Detector (KAGRA) in Japan. Ideally, all three observatories should detect a gravitational wave event to confirm it.
Bottom line: A new study suggests the largest stellar-mass black holes form not from single stars collapsing, but from collisions and mergers between smaller black holes.
This illustration shows 2 black holes spiraling toward a colossal collision. A new study says mergers like this could explain how mysteriously large black holes form. Image via LIGO/ Caltech/ Simulating eXtreme Spacetimes Collaboration.
Over the past decade, astronomers have detected many black holes that seem too massive to have formed from the collapse of a single star. So how did they form?
Researchers have just found new evidence that these black holes form from chaotic collisions between multiple smaller black holes.
The finding comes from studying ripples in the fabric of spacetime that these black holes send out into the universe.
A new study has provided fresh evidence that some of the largest stellar-mass black holes didn’t form directly from the collapse of massive stars. Instead, the research suggests, they were built from chaotic collisions and repeated mergers between multiple smaller black holes.
Stellar-mass black holes are black holes ranging from a few times the mass of our sun to tens of solar masses. And on May 7, 2026, the researchers said they’ve identified two distinct populations of these black holes.
The first population, those less than 45 times the mass of our sun, formed as we’d typically expect: from stars collapsing at the end of their lives. But the second population – those over 45 solar masses – is more mysterious. Astronomers have long suspected that these are too massive to have formed from the collapse of single stars. And the new research helps explain how they’ve come to exist.
The scientists noticed that these larger black holes are spinning faster and in much more varied directions than the smaller ones. They say this is evidence that the larger black holes are the product of black hole collisions in the maelstrom of dense star clusters.
They performed this study using new data from gravitational waves observations. The research team analyzed data from a catalog of observations, called the LIGO–Virgo–KAGRA Gravitational-Wave Transient Catalog version 4 (GWTC4). In it, they found 153 detections of black hole mergers.
Gravitational wave astronomy is now doing more than counting black hole mergers. It is starting to reveal how black holes grow, where they grow, and what that tells us about the lives and deaths of massive stars. This is exciting because we can use the information to test our understanding of how stars and [star] clusters evolve in the universe.
The team published its findings in the peer-reviewed journal Nature Astronomy on May 7, 2026.
Detecting ripples in spacetime
A black hole first forms when a massive star runs out of fuel for nuclear fusion. As a result, it collapses under its own gravity. The star’s mass becomes so compact that nothing can escape its powerful gravitational force … not even light.
In dense star clusters, two black holes often get close enough to start orbiting each other. As the two objects rotate, they generate a unique pattern of gravitational waves, or ripples in the fabric of the universe. The wave characteristics depend on the mass of each object, as well as their distance and orbit orientation from Earth.
This computer simulation shows the merger of 2 black holes. As the black holes spiral toward each other, collide and merge, they create gravitational waves. Scientists made this simulation using equations from Albert Einstein’s theory of general relativity and data from the Laser Interferometer Gravitational-wave Observatory (LIGO). Video via the Simulating eXtreme Spacetimes (SXS) project.
The orbiting black hole pair radiates gravitational waves, resulting in some loss of orbital energy. As a result, the black holes get closer. That causes them to orbit each other faster, which radiates even stronger gravitational waves, which makes them get closer, and so on. The final outcome is a violent merger of the two objects.
Gravitational wave laser interferometers are able to detect the final orbits of the black holes just before the merger, which occurs over a timeframe of seconds.
Two populations of black holes
The scientists analyzed 153 black hole mergers in the LIGO–Virgo–KAGRA’s Gravitational-Wave Transient Catalog version 4. This catalog is a compilation of all gravitational wave detections from May 2023 to January 2024.
They noticed two distinct populations of stellar black holes. Isobel Romero-Shaw, also of Cardiff University, said:
What surprised us most was how clearly the high mass black holes [over 45 solar masses] stand out as a separate population.
Unlike the lower mass systems we analyzed, which were generally slowly-spinning, the higher mass systems are consistent with having more rapid spins, oriented in seemingly random directions. This is the exact signature you would expect if black holes were repeatedly merging in dense star clusters.
Messier 80 is a dense globular star cluster, about 28,000 light-years away, in the constellation Scorpius the Scorpion. The new study suggests that huge stellar-mass black holes form via chaotic collisions between multiple smaller black holes in dense star clusters like this. Image via NASA, ESA, G. Piotto, and G. Kober.
The pair-instability mass gap
There’s a theory in stellar evolution called the pair-instability mass gap. It states that stars above a certain mass limit will violently explode, rather than becoming a black hole. In their study, the team established that this limit was 45 solar masses. Therefore, any star over that value would explode at the end of its lifetime.
According to this theory, a collapsing star wouldn’t be able to form a black hole over 45 solar masses. However, gravitational wave detections have shown that stellar-mass black holes over this threshold do indeed exist.
Antonini said:
In our study we find evidence for the long-predicted pair-instability mass gap — a range of masses where stars are not expected to leave behind black holes at all. Gravitational wave detectors have successfully found black holes that appear to sit in or near that gap, which we identify at around 45 solar masses.
So how did these huge black holes form? The answer, Antonini says, lies in their spin:
The biggest black holes in the current sample seem to be telling us about [star] cluster dynamics, not just stellar evolution. Above about 45 solar masses the [black hole] spin distribution changes in a way that is hard to explain with normal stellar binaries alone but is naturally explained if these black holes have already been through earlier mergers in dense [star] clusters.
So the smaller black holes have similar spins, having formed from a population of similar stars. But when the black holes cross this 45-solar-mass line, they start to show a wide range of different spin speeds and orientations. The researchers think this erratic spinning is a sign that the large black holes have been through a series of violent collisions and mergers.
How gravitational wave laser interferometers work
If you threw two stones into a pond, each stone creates concentric ripples. The sections where the ripples intersect are called interference patterns. Gravitational wave laser interferometers look for laser beam interference patterns caused by gravitational waves.
A gravitational wave observatory has two long, perpendicular arms. For instance, at the LIGO observatories in Washington and Louisiana, each arm is 2.5 miles (4 km) long. A laser beam is split to shine along each arm. At the end of the arm, a mirror reflects the beam back and the two beams meet to form an interference pattern.
When gravitational waves pass through, spacetime itself oscillates. As a result, each wave stretches one arm and compresses the other. Therefore, the lasers move through slightly different lengths. The resulting interference patterns reveal information about the objects that generated the gravitational waves. This instrument is so sensitive that it can detect an arm length difference that’s 1/10,000th the width of a proton.
A brief animation showing the basic operation of the LIGO interferometer. Video via LIGO/ Einstein’s Messengers/ NSF.
Besides LIGO, there are two other gravitational wave observatories: the Virgo interferometer in Italy and the Kamioka Gravitational Wave Detector (KAGRA) in Japan. Ideally, all three observatories should detect a gravitational wave event to confirm it.
Bottom line: A new study suggests the largest stellar-mass black holes form not from single stars collapsing, but from collisions and mergers between smaller black holes.
View at EarthSky Community Photos. | Eddie Little of North Carolina captured the stars circling around Polaris, the North Star, on January 2, 2025, and wrote: “I had a mostly cloudless, nearly moonless night on one of the longest nights of the year. Approximately 12 hours of shooting.” Thank you, Eddie!
Polaris is the North Star
The North Star or Pole Star – aka Polaris – is famous for holding nearly still in our sky while the entire northern sky moves around it. That’s because it’s located very close to the north celestial pole: the point around which the entire northern sky turns.
Polaris is not the brightest star in the nighttime sky, despite the common belief. In fact, it’s only the 47th brightest star. But you can find it easily, and, once you do, you’ll see it shining in the northern sky every night from Northern Hemisphere locations.
Polaris marks the spot that is due north. As you face Polaris and stretch your arms sideways, your right hand points due east, and your left hand points due west. Then, an about-face from Polaris steers you due south.
Star trails shown circling around Polaris, the North Star. Image via Good Free Photos/ Unsplash.
A star to steer by
In a dark country sky, even when the full moon obscures a good deal of the starry heavens, the North Star is relatively easy to see. That fact has made this star a boon to travelers throughout the Northern Hemisphere, both over land and sea. So finding Polaris means you know the direction north.
Best of all, you can readily find Polaris by using the prominent group of stars known as the Big Dipper, called the Plough in the United Kingdom, which may be the Northern Hemisphere’s most famous star pattern. To locate Polaris, all you have to do is to find the Big Dipper pointer starsDubhe and Merak. These two stars outline the outer part of the Big Dipper’s bowl. Simply draw a line from Merak through Dubhe, and go about five times the Merak/Dubhe distance to Polaris.
If you can find the Big Dipper, you can find Polaris. The 2 outer stars in the bowl of the Dipper – Dubhe and Merak – always point to the North Star. Chart via EarthSky.
This clock runs backward
Polaris marks the center of nature’s grandest celestial clock!
The Big Dipper, like a great big hour hand, goes full circle around Polaris in one day. More specifically, the Big Dipper circles Polaris – in a counterclockwise direction – in 23 hours and 56 minutes. You could set your watch by it!
Although the Big Dipper travels around Polaris all night long, the Big Dipper pointer stars always point to Polaris at any time of the night, and on any day of the year.
It’s part of the Little Dipper
Polaris is also famous for marking the end of the Little Dipper‘s handle. The Little Dipper is tougher to spot in the night sky than the Big Dipper. But if you use the Big Dipper’s pointer stars to locate Polaris, you’ll be one step closer to seeing the Little Dipper.
The Big Dipper leads you to the Little Dipper. Polaris marks the end of the handle of the Little Dipper. Chart via EarthSky.
Its height in the sky depends on your location
As you travel northward, Polaris climbs higher in the sky. If you go as far north as the North Pole, you’ll see Polaris directly overhead.
As you travel south, Polaris drops closer to the northern horizon.
If you get as far as the equator, Polaris sinks to the horizon.
South of the equator, Polaris drops below the northern horizon.
Trusting Polaris with their lives
At one time in human history, people literally depended on their lucky stars for their lives and livelihood. Luckily, they could trust the Big Dipper and the North Star to guide them. People could sail the seas and cross the trackless deserts without getting lost. When slavery existed in the United States, people escaping slavery counted on the Big Dipper to show them the North Star, lighting their way to the free states and Canada.
While being honored as the North Star, Polaris enjoys the title of Lodestar and Cynosure as well.
Stargazers in the Southern Hemisphere can’t use Polaris to find the direction north. That’s because – as seen from Earth’s equator, and southward – this northernmost, moderately bright star remains permanently below the northern horizon. Instead, to find the south celestial pole, we rely on the distinctive Southern Cross.
By extending an imaginary line through the Southern Cross’ two pointer stars, Alpha and Beta Centauri, and drawing a triangle with the cross, we can locate the South Celestial Pole. This point in the sky acts like a pole star, guiding us in our navigation.
But wait, is there no pole star in the South?
Well, technically yes, there is a southern pole star: Sigma Octantis. Sometimes called Polaris Australis, this star is in the Octans constellation. It lies approximately 1 degree away from the south celestial pole.
Sigma Octantis is around 4.4 times the radius of the sun and radiates roughly 44 times more energy. Yet despite its impressive size and luminosity, its distance of 294 light-years means it appears extremely faint from Earth. It glows at just magnitude 5.5, making it visible only under dark skies and to observers with keen eyesight.
As a result, for many centuries, both European navigators and Polynesian sailors have had to rely on the Southern Cross to guide them across oceans. Like Polaris in the north, the Southern Cross and its pointer stars are circumpolar for much of the southern hemisphere, meaning they never set below the horizon and can be seen year-round.
Today, the Southern Cross proudly adorns the New Zealand and Australian national flag, a testament to its enduring importance as a celestial compass and a beacon for navigation.
History of Polaris
Polaris hasn’t always been the North Star and won’t remain the North Star forever. For example, a famous star called Thuban, in the constellation Draco the Dragon, was the North Star when the Egyptians built the pyramids.
But Polaris is a good North Star because it’s the sky’s 48th brightest star. So it’s noticeable in the sky. It served well as the North Star, for example, when the Europeans first sailed across the Atlantic over five centuries ago.
And Polaris will continue its reign as the North Star for many centuries to come. It will align most closely with the north celestial pole – the point in the sky directly above Earth’s north rotational axis – on March 24, 2100. The computational wizard Jean Meeus figures Polaris will be 27′ 09″ (0.4525 degrees) from the north celestial pole at that time (a little less than the angular diameter of the moon when at its farthest from Earth).
Meanwhile, there is currently no visible star marking the celestial pole in the Southern Hemisphere. What’s more, the Southern Hemisphere won’t see a pole star appreciably close to the south celestial pole for another 2,000 years.
Polaris is a triple star
The single point of light that we see as Polaris is a triple star system, or three stars orbiting a common center of mass. The primary star, Polaris A, is a supergiant with about six times the mass of our sun. A close companion, Polaris Ab, orbits 2 billion miles (3.2 billion km) from Polaris. You are unlikely to ever see this star, because it is very close to Polaris.
Much farther away, near the top of this illustration, is the third companion, Polaris B. Polaris B, with magnitude 8.7, is located approximately 240 billion miles (390 billion km) from Polaris A. This translates to 18.4 arcseconds, and you can discern – split – these two stars in a small telescope. This split is always a hit at public star parties. The two companion stars have the same temperature as Polaris A but are dwarf stars.
Artist’s concept of Polaris and its two known companion stars. Image via NASA/ Wikimedia Commons.
Star bright, star light
Astronomers estimate Polaris’ distance at 434 light-years. Considering the distance, Polaris must be a respectably luminous star. Polaris is a yellow supergiant star shining with the luminosity of 1,260 suns.
And it varies in brightness, too!
Polaris is a variable star. In the past, it had varied between magnitudes 1.86 and 2.13 every four days. In recent decades, this variability decreased from 10% to 2%, then it went back up to 4% variability. Astronomers are not sure why this happened. It’s the type of variable star known as a Cepheid variable star, a class of stars that astronomers use to figure distances to star clusters and galaxies.
Seeing Polaris in a telescope during the day
Since Polaris hardly moves, this makes it easy to see in the daytime. Set your telescope on Polaris in the early morning, before dawn. Focus sharply on it. Turn off your clock drive, if you have one, and keep your telescope stationary. Come back just after sunrise and look for it again. It should still be in your field of view, having moved about 30 arcminutes in the past three hours.
What’s the RA today?
In the year 2000, Polaris’ position was RA: 2h 31m 48.7s, dec: +89° 15′ 51″. Due to precession, since this star is so close to the celestial north pole, its Right Ascension (RA) can change quickly. Presently it is sitting at about 03h 00m. Here is a graph showing how the RA of the star changes over the next century.
The right ascension of Polaris for the next century. Graph by Don Machholz using data from Stub Mandrel.
The view of Polaris you will never see: the Integrated Flux Nebula
Just when you think you have seen it all … maybe you have. Because this next bit will blow your mind, and you will never visually see it. Below we see an image of Polaris, which is several images stacked to bring out the contrast. Those are not clouds in our atmosphere. They are not clouds between us and Polaris. They are clouds well beyond Polaris, illuminated by the light of our galaxy. These clouds are called the Integrated Flux Nebula.
An example of the faint integrated flux nebula around the star Polaris. Image via Kush Chandaria/ Wikipedia (CC BY-SA 4.0).
Bottom line: Polaris is the North Star, and the entire northern sky wheels around it. But it’s not the brightest star in the sky. In fact, Polaris ranks only 48th in brightness.
View at EarthSky Community Photos. | Eddie Little of North Carolina captured the stars circling around Polaris, the North Star, on January 2, 2025, and wrote: “I had a mostly cloudless, nearly moonless night on one of the longest nights of the year. Approximately 12 hours of shooting.” Thank you, Eddie!
Polaris is the North Star
The North Star or Pole Star – aka Polaris – is famous for holding nearly still in our sky while the entire northern sky moves around it. That’s because it’s located very close to the north celestial pole: the point around which the entire northern sky turns.
Polaris is not the brightest star in the nighttime sky, despite the common belief. In fact, it’s only the 47th brightest star. But you can find it easily, and, once you do, you’ll see it shining in the northern sky every night from Northern Hemisphere locations.
Polaris marks the spot that is due north. As you face Polaris and stretch your arms sideways, your right hand points due east, and your left hand points due west. Then, an about-face from Polaris steers you due south.
Star trails shown circling around Polaris, the North Star. Image via Good Free Photos/ Unsplash.
A star to steer by
In a dark country sky, even when the full moon obscures a good deal of the starry heavens, the North Star is relatively easy to see. That fact has made this star a boon to travelers throughout the Northern Hemisphere, both over land and sea. So finding Polaris means you know the direction north.
Best of all, you can readily find Polaris by using the prominent group of stars known as the Big Dipper, called the Plough in the United Kingdom, which may be the Northern Hemisphere’s most famous star pattern. To locate Polaris, all you have to do is to find the Big Dipper pointer starsDubhe and Merak. These two stars outline the outer part of the Big Dipper’s bowl. Simply draw a line from Merak through Dubhe, and go about five times the Merak/Dubhe distance to Polaris.
If you can find the Big Dipper, you can find Polaris. The 2 outer stars in the bowl of the Dipper – Dubhe and Merak – always point to the North Star. Chart via EarthSky.
This clock runs backward
Polaris marks the center of nature’s grandest celestial clock!
The Big Dipper, like a great big hour hand, goes full circle around Polaris in one day. More specifically, the Big Dipper circles Polaris – in a counterclockwise direction – in 23 hours and 56 minutes. You could set your watch by it!
Although the Big Dipper travels around Polaris all night long, the Big Dipper pointer stars always point to Polaris at any time of the night, and on any day of the year.
It’s part of the Little Dipper
Polaris is also famous for marking the end of the Little Dipper‘s handle. The Little Dipper is tougher to spot in the night sky than the Big Dipper. But if you use the Big Dipper’s pointer stars to locate Polaris, you’ll be one step closer to seeing the Little Dipper.
The Big Dipper leads you to the Little Dipper. Polaris marks the end of the handle of the Little Dipper. Chart via EarthSky.
Its height in the sky depends on your location
As you travel northward, Polaris climbs higher in the sky. If you go as far north as the North Pole, you’ll see Polaris directly overhead.
As you travel south, Polaris drops closer to the northern horizon.
If you get as far as the equator, Polaris sinks to the horizon.
South of the equator, Polaris drops below the northern horizon.
Trusting Polaris with their lives
At one time in human history, people literally depended on their lucky stars for their lives and livelihood. Luckily, they could trust the Big Dipper and the North Star to guide them. People could sail the seas and cross the trackless deserts without getting lost. When slavery existed in the United States, people escaping slavery counted on the Big Dipper to show them the North Star, lighting their way to the free states and Canada.
While being honored as the North Star, Polaris enjoys the title of Lodestar and Cynosure as well.
Stargazers in the Southern Hemisphere can’t use Polaris to find the direction north. That’s because – as seen from Earth’s equator, and southward – this northernmost, moderately bright star remains permanently below the northern horizon. Instead, to find the south celestial pole, we rely on the distinctive Southern Cross.
By extending an imaginary line through the Southern Cross’ two pointer stars, Alpha and Beta Centauri, and drawing a triangle with the cross, we can locate the South Celestial Pole. This point in the sky acts like a pole star, guiding us in our navigation.
But wait, is there no pole star in the South?
Well, technically yes, there is a southern pole star: Sigma Octantis. Sometimes called Polaris Australis, this star is in the Octans constellation. It lies approximately 1 degree away from the south celestial pole.
Sigma Octantis is around 4.4 times the radius of the sun and radiates roughly 44 times more energy. Yet despite its impressive size and luminosity, its distance of 294 light-years means it appears extremely faint from Earth. It glows at just magnitude 5.5, making it visible only under dark skies and to observers with keen eyesight.
As a result, for many centuries, both European navigators and Polynesian sailors have had to rely on the Southern Cross to guide them across oceans. Like Polaris in the north, the Southern Cross and its pointer stars are circumpolar for much of the southern hemisphere, meaning they never set below the horizon and can be seen year-round.
Today, the Southern Cross proudly adorns the New Zealand and Australian national flag, a testament to its enduring importance as a celestial compass and a beacon for navigation.
History of Polaris
Polaris hasn’t always been the North Star and won’t remain the North Star forever. For example, a famous star called Thuban, in the constellation Draco the Dragon, was the North Star when the Egyptians built the pyramids.
But Polaris is a good North Star because it’s the sky’s 48th brightest star. So it’s noticeable in the sky. It served well as the North Star, for example, when the Europeans first sailed across the Atlantic over five centuries ago.
And Polaris will continue its reign as the North Star for many centuries to come. It will align most closely with the north celestial pole – the point in the sky directly above Earth’s north rotational axis – on March 24, 2100. The computational wizard Jean Meeus figures Polaris will be 27′ 09″ (0.4525 degrees) from the north celestial pole at that time (a little less than the angular diameter of the moon when at its farthest from Earth).
Meanwhile, there is currently no visible star marking the celestial pole in the Southern Hemisphere. What’s more, the Southern Hemisphere won’t see a pole star appreciably close to the south celestial pole for another 2,000 years.
Polaris is a triple star
The single point of light that we see as Polaris is a triple star system, or three stars orbiting a common center of mass. The primary star, Polaris A, is a supergiant with about six times the mass of our sun. A close companion, Polaris Ab, orbits 2 billion miles (3.2 billion km) from Polaris. You are unlikely to ever see this star, because it is very close to Polaris.
Much farther away, near the top of this illustration, is the third companion, Polaris B. Polaris B, with magnitude 8.7, is located approximately 240 billion miles (390 billion km) from Polaris A. This translates to 18.4 arcseconds, and you can discern – split – these two stars in a small telescope. This split is always a hit at public star parties. The two companion stars have the same temperature as Polaris A but are dwarf stars.
Artist’s concept of Polaris and its two known companion stars. Image via NASA/ Wikimedia Commons.
Star bright, star light
Astronomers estimate Polaris’ distance at 434 light-years. Considering the distance, Polaris must be a respectably luminous star. Polaris is a yellow supergiant star shining with the luminosity of 1,260 suns.
And it varies in brightness, too!
Polaris is a variable star. In the past, it had varied between magnitudes 1.86 and 2.13 every four days. In recent decades, this variability decreased from 10% to 2%, then it went back up to 4% variability. Astronomers are not sure why this happened. It’s the type of variable star known as a Cepheid variable star, a class of stars that astronomers use to figure distances to star clusters and galaxies.
Seeing Polaris in a telescope during the day
Since Polaris hardly moves, this makes it easy to see in the daytime. Set your telescope on Polaris in the early morning, before dawn. Focus sharply on it. Turn off your clock drive, if you have one, and keep your telescope stationary. Come back just after sunrise and look for it again. It should still be in your field of view, having moved about 30 arcminutes in the past three hours.
What’s the RA today?
In the year 2000, Polaris’ position was RA: 2h 31m 48.7s, dec: +89° 15′ 51″. Due to precession, since this star is so close to the celestial north pole, its Right Ascension (RA) can change quickly. Presently it is sitting at about 03h 00m. Here is a graph showing how the RA of the star changes over the next century.
The right ascension of Polaris for the next century. Graph by Don Machholz using data from Stub Mandrel.
The view of Polaris you will never see: the Integrated Flux Nebula
Just when you think you have seen it all … maybe you have. Because this next bit will blow your mind, and you will never visually see it. Below we see an image of Polaris, which is several images stacked to bring out the contrast. Those are not clouds in our atmosphere. They are not clouds between us and Polaris. They are clouds well beyond Polaris, illuminated by the light of our galaxy. These clouds are called the Integrated Flux Nebula.
An example of the faint integrated flux nebula around the star Polaris. Image via Kush Chandaria/ Wikipedia (CC BY-SA 4.0).
Bottom line: Polaris is the North Star, and the entire northern sky wheels around it. But it’s not the brightest star in the sky. In fact, Polaris ranks only 48th in brightness.
