The volcano Anak Krakatau – or Child of Krakatoa – underwent an eruption in Indonesia from September 4 to 6, 2026. Eight people are missing as a result of the eruption. The OLI (Operational Land Imager) on the Landsat 8 satellite acquired this image on September 5, 2026. Image via NASA’s Earth Observatory/ Michala Garrison.
Anak Krakatau erupts in Indonesia
In 1883, Krakatoa volcano in Indonesia erupted so powerfully that it destroyed the majority of its island, triggering 120-foot tsunami waves and producing the loudest sound in recorded history. In 1927, Anak Krakatau – or Child of Krakatoa, emerged from the old caldera. Anak Krakatau erupts fairly regularly. And on September 4, 2026, it roared back to activity, belching gas and ash into the atmosphere. The eruption snarled air traffic in the area. And, while the island itself is no longer inhabited, a boat of eight people, five of them journalists, were headed toward Anak Krakatau to cover the story. After reaching the vicinity of the island, the boat went missing.
In the photo above, the Landsat 8 satellite captured the erupting volcano on September 5. By the next day, the smoke plume had reached 20,000 feet (6,000 m) high to the east and 50,000 feet (15,000 m) to the west.
In a video from September 5, another boat – a fishing boat – captured scenes of the eruption as debris pelted the water all around them.
Mount Anak Krakatau in Indonesia is on its second straight day of a major eruption. Volcanic ash has caused the suspension of flights out of Jakarta's main airport.
For now, the eruptive period has ended and air travel has resumed. Anak Krakatau regularly erupts, usually in a more mild manner, but these larger outbursts are also not unusual. In 2018, Anak Krakatau erupted and caused part of its island to collapse. That collapse triggered a tsunami that killed 437 in Java and Sumatra.
What to expect: Likely smaller explosions than the eruption that occurred on September 6 but continued blasts will almost certainly happen. The PVMBG [Indonesia’s Center for Volcanology and Geological Hazard Mitigation] will be watching to see what the seismic activity at the volcano looks like to suggest whether more magma is rising up into the upper parts of the volcanic system. The seismic data for the past few months shows the sharp increase in earthquakes and tremor starting in late August before these new eruptions began.
And while PVMBG did report six volcanoes erupting simultaneously in Indonesia on August 31, this is not unusual behavior for a country on the Ring of Fire.
Bottom line: Anak Krakatau erupted in early September, sending a long plume of gas and ash into the atmosphere. Eight people, including 5 journalists who headed toward the eruption by boat, are now missing.
The volcano Anak Krakatau – or Child of Krakatoa – underwent an eruption in Indonesia from September 4 to 6, 2026. Eight people are missing as a result of the eruption. The OLI (Operational Land Imager) on the Landsat 8 satellite acquired this image on September 5, 2026. Image via NASA’s Earth Observatory/ Michala Garrison.
Anak Krakatau erupts in Indonesia
In 1883, Krakatoa volcano in Indonesia erupted so powerfully that it destroyed the majority of its island, triggering 120-foot tsunami waves and producing the loudest sound in recorded history. In 1927, Anak Krakatau – or Child of Krakatoa, emerged from the old caldera. Anak Krakatau erupts fairly regularly. And on September 4, 2026, it roared back to activity, belching gas and ash into the atmosphere. The eruption snarled air traffic in the area. And, while the island itself is no longer inhabited, a boat of eight people, five of them journalists, were headed toward Anak Krakatau to cover the story. After reaching the vicinity of the island, the boat went missing.
In the photo above, the Landsat 8 satellite captured the erupting volcano on September 5. By the next day, the smoke plume had reached 20,000 feet (6,000 m) high to the east and 50,000 feet (15,000 m) to the west.
In a video from September 5, another boat – a fishing boat – captured scenes of the eruption as debris pelted the water all around them.
Mount Anak Krakatau in Indonesia is on its second straight day of a major eruption. Volcanic ash has caused the suspension of flights out of Jakarta's main airport.
For now, the eruptive period has ended and air travel has resumed. Anak Krakatau regularly erupts, usually in a more mild manner, but these larger outbursts are also not unusual. In 2018, Anak Krakatau erupted and caused part of its island to collapse. That collapse triggered a tsunami that killed 437 in Java and Sumatra.
What to expect: Likely smaller explosions than the eruption that occurred on September 6 but continued blasts will almost certainly happen. The PVMBG [Indonesia’s Center for Volcanology and Geological Hazard Mitigation] will be watching to see what the seismic activity at the volcano looks like to suggest whether more magma is rising up into the upper parts of the volcanic system. The seismic data for the past few months shows the sharp increase in earthquakes and tremor starting in late August before these new eruptions began.
And while PVMBG did report six volcanoes erupting simultaneously in Indonesia on August 31, this is not unusual behavior for a country on the Ring of Fire.
Bottom line: Anak Krakatau erupted in early September, sending a long plume of gas and ash into the atmosphere. Eight people, including 5 journalists who headed toward the eruption by boat, are now missing.
This video from the CCOR-1 coronagraph aboard GOES-19 – acquired on September 10, 2026 – blocks the sun’s bright face. So we can watch the faint outer corona, and the space near the sun. You can see a far-side eruption, blasting outward from behind the occulting disk. Also, the moon drifts into the field of view from the right, then slips back out the same way. Did the moon make a turn in orbit? No. Astronomers would say that the moon in this image is exhibiting retrograde motion. The apparent turn is a perspective effect … an illusion. It happens because moon orbits Earth only once each month. The spacecraft moves much faster, completing an orbit around Earth in just one day. So, from the spacecraft’s perspective, it’s as if the moon is a moving car on the highway, with a faster car (our spacecraft) passing it. From the spacecraft’s perspective, for a time, the slower moon appears to move backwards. Image via NOAA.
The retrograde or “backward” motion of a planet is an illusion, a trick of perspective.
Most retrograde motion is an illusion
As measured against the fixed stars, planets typically appear to move eastward throughout the year. But, sometimes, they seem to pause briefly in this eastward motion. They reach what astronomers call a stationary point. Then, for some months, the planet moves westward (backward) in front of the stars. For example, Mars will reach its next stationary point on January 10, 2027. Astronomers (and astrologers) call a planet’s westward motion its retrograde motion.
Though it baffled ancient stargazers, we know now that this type of retrograde motion is an illusion.
You can experience this illusion in an earthbound way, the next time you pass a car on the highway. As you approach a slower car, it’s clearly moving in the same direction you are. But, as you pull alongside and pass it – from your vantage point in the faster car – the slower car may appear to move backwards for a moment. Then, as you pull ahead of it, the car appears to resume its forward motion.
The same thing happens whenever Earth prepares to pass a slower-moving planet whose orbit is bigger than ours. Earth is due to pass between Mars and the sun on February 19, 2027. When we go between the sun and Mars (or another outer planet), these planets – all of which move more slowly than Earth in orbit – appear to reverse course in our sky.
An animation showing the retrograde motion of Mars in the summer of 2003. Planets typically move toward the east in front of the stars. When they move west, they’re said to be undergoing retrograde motion. The illusion is caused by our perspective, as seen from Earth. Image via Wikimedia Commons (CC BY-SA 4.0).A schematic of how retrograde motion works when Earth (T) passes an outer planet (P) as they both orbit the sun (S). The changing viewing angle from Earth makes the projection of the planet against the celestial sphere (A) move backwards (A2-A4) as we pass the slower, outer planet. Image via Wikimedia Commons (CC BY-SA 3.0).
Retrograde motion in inner planets
The above description helps you understand why we see retrograde motion in outer planets. But we can see it in inner planets, too! It just works a bit differently.
We always see the inner planets relatively close to the sun. They can never be opposite the sun in our sky because they are on an orbit inside ours. So we see them before sunrise or after sunset. Venus and Mercury also move east to west daily in our skies (because Earth spins west to east). But because these inner planets are speedier than Earth, we can see them – over the course of days or weeks – rise away from the morning sun. Then as they turn the corner to go behind the sun, from our perspective it looks like they’re falling back toward the sun. At these times, their motion slows as they reach their apex, and then the motion reverses.
In fact, Mercury is the planet that experiences retrograde most often. An Earth-year is 365 days, but Mercury circles the sun in just 88 days. So a few times a year, Mercury is moving away from the sun in the morning or evening sky and then falling back toward it.
It baffled early astronomers
Early astronomers believed Earth lay at the center of the universe. And so they went to complicated lengths to attempt to explain retrograde motion in that Earth-centered universe. They theorized each planet not only orbited Earth, but also spun around a moving point on their orbit known as an epicycle.
Imagine whipping a ball on a length of string around your hand while you turned in place. That’s similar to the ancient view of retrograde motion.
When it became generally accepted that Earth and the other planets orbited the sun, suddenly retrograde motion made a lot more sense.
A schematic of how astronomers envisioned the motion of the planets before Copernicus. The Earth sat near the center of the universe. The planets moved around a small circle (the epicycle) which in turn moved along a larger circle (the deferent). The deferent was centered on a point (X) midway between the Earth and another spot called the equant. Image via Wikimedia Commons.
Retrograde motion on other worlds
If you could see the sky from another planet besides Earth, retrograde illusions would lead to your seeing some very strange phenomena. On Mercury, for example, the sun sometimes appears to move in retrograde. As Mercury speeds through its closest approach to the sun, its orbital speed overtakes its rotational speed. An astronaut on the surface would see the sun partially rise, then dip back below the horizon, then rise again before resuming its east-to-west trek across the sky. The result is that, once a year, Mercury gets two sunrises on the same day!
— Seven Machina Rasmussen (@toomanyspectra) April 22, 2024
Other retrograde motion is real
Astronomers also use the word retrograde to describe true backward motion among planets and moons.
Venus, for example, rotates or spins on its axis in the opposite direction from every other planet in the solar system. If the clouds ever parted, hypothetical Venusians would see the sun rise in the west and set in the east. Astronomers would say that Venus rotates in a retrograde manner.
Some moons also have retrograde orbits around their planets. In other words, most of the large moons orbit in the same direction that their planet spins … but not Triton, for example, the largest moon of Neptune. It orbits opposite the direction of Neptune’s spin.
Among the smaller asteroid-like moons that swarm about the giant planets, many have retrograde orbits.
It’s the same word: retrograde. But now there’s no illusion. Whether speaking of a planet’s rotation – or its orbit – if it’s opposite what you’d expect, astronomers call it retrograde.
A photomosaic from Voyager 2 of Neptune’s largest moon, Triton. The moon orbits Neptune opposite the direction that the planet rotates. Does this mean that Triton came from the Kuiper Belt and was eventually captured by the ice giant? Image via NASA.
How does it happen?
According to modern astronomers, a true retrograde orbit for an orbiting moon most likely stems from a capture. Triton, for example, might have come out of the Kuiper Belt, the region of icy debris beyond Neptune. Perhaps a collision in the belt sent Triton careening inward toward the sun. A close encounter with Neptune could have slowed it down, forcing it to settle into a backward orbit.
In past decades, astronomers have also discovered planets in distant solar systems with retrograde orbits. These exoplanets orbit their suns in the opposite direction from how the star rotates.
It’s puzzling, because planets form out of debris disks that orbit young stars. And those orbiting disks share the star’s rotation. So how does a planet end up with a true backward orbit? The only way – some astronomers believe – is either by a near-collision with another planet, or if another star once passed too close to the system.
Either way, close encounters can disrupt the orbits of planets and set them on a backward path!
Bottom line: What is retrograde motion? See an image that appears to show the moon moving backwards! An explanation, and more bizarre examples, here.
This video from the CCOR-1 coronagraph aboard GOES-19 – acquired on September 10, 2026 – blocks the sun’s bright face. So we can watch the faint outer corona, and the space near the sun. You can see a far-side eruption, blasting outward from behind the occulting disk. Also, the moon drifts into the field of view from the right, then slips back out the same way. Did the moon make a turn in orbit? No. Astronomers would say that the moon in this image is exhibiting retrograde motion. The apparent turn is a perspective effect … an illusion. It happens because moon orbits Earth only once each month. The spacecraft moves much faster, completing an orbit around Earth in just one day. So, from the spacecraft’s perspective, it’s as if the moon is a moving car on the highway, with a faster car (our spacecraft) passing it. From the spacecraft’s perspective, for a time, the slower moon appears to move backwards. Image via NOAA.
The retrograde or “backward” motion of a planet is an illusion, a trick of perspective.
Most retrograde motion is an illusion
As measured against the fixed stars, planets typically appear to move eastward throughout the year. But, sometimes, they seem to pause briefly in this eastward motion. They reach what astronomers call a stationary point. Then, for some months, the planet moves westward (backward) in front of the stars. For example, Mars will reach its next stationary point on January 10, 2027. Astronomers (and astrologers) call a planet’s westward motion its retrograde motion.
Though it baffled ancient stargazers, we know now that this type of retrograde motion is an illusion.
You can experience this illusion in an earthbound way, the next time you pass a car on the highway. As you approach a slower car, it’s clearly moving in the same direction you are. But, as you pull alongside and pass it – from your vantage point in the faster car – the slower car may appear to move backwards for a moment. Then, as you pull ahead of it, the car appears to resume its forward motion.
The same thing happens whenever Earth prepares to pass a slower-moving planet whose orbit is bigger than ours. Earth is due to pass between Mars and the sun on February 19, 2027. When we go between the sun and Mars (or another outer planet), these planets – all of which move more slowly than Earth in orbit – appear to reverse course in our sky.
An animation showing the retrograde motion of Mars in the summer of 2003. Planets typically move toward the east in front of the stars. When they move west, they’re said to be undergoing retrograde motion. The illusion is caused by our perspective, as seen from Earth. Image via Wikimedia Commons (CC BY-SA 4.0).A schematic of how retrograde motion works when Earth (T) passes an outer planet (P) as they both orbit the sun (S). The changing viewing angle from Earth makes the projection of the planet against the celestial sphere (A) move backwards (A2-A4) as we pass the slower, outer planet. Image via Wikimedia Commons (CC BY-SA 3.0).
Retrograde motion in inner planets
The above description helps you understand why we see retrograde motion in outer planets. But we can see it in inner planets, too! It just works a bit differently.
We always see the inner planets relatively close to the sun. They can never be opposite the sun in our sky because they are on an orbit inside ours. So we see them before sunrise or after sunset. Venus and Mercury also move east to west daily in our skies (because Earth spins west to east). But because these inner planets are speedier than Earth, we can see them – over the course of days or weeks – rise away from the morning sun. Then as they turn the corner to go behind the sun, from our perspective it looks like they’re falling back toward the sun. At these times, their motion slows as they reach their apex, and then the motion reverses.
In fact, Mercury is the planet that experiences retrograde most often. An Earth-year is 365 days, but Mercury circles the sun in just 88 days. So a few times a year, Mercury is moving away from the sun in the morning or evening sky and then falling back toward it.
It baffled early astronomers
Early astronomers believed Earth lay at the center of the universe. And so they went to complicated lengths to attempt to explain retrograde motion in that Earth-centered universe. They theorized each planet not only orbited Earth, but also spun around a moving point on their orbit known as an epicycle.
Imagine whipping a ball on a length of string around your hand while you turned in place. That’s similar to the ancient view of retrograde motion.
When it became generally accepted that Earth and the other planets orbited the sun, suddenly retrograde motion made a lot more sense.
A schematic of how astronomers envisioned the motion of the planets before Copernicus. The Earth sat near the center of the universe. The planets moved around a small circle (the epicycle) which in turn moved along a larger circle (the deferent). The deferent was centered on a point (X) midway between the Earth and another spot called the equant. Image via Wikimedia Commons.
Retrograde motion on other worlds
If you could see the sky from another planet besides Earth, retrograde illusions would lead to your seeing some very strange phenomena. On Mercury, for example, the sun sometimes appears to move in retrograde. As Mercury speeds through its closest approach to the sun, its orbital speed overtakes its rotational speed. An astronaut on the surface would see the sun partially rise, then dip back below the horizon, then rise again before resuming its east-to-west trek across the sky. The result is that, once a year, Mercury gets two sunrises on the same day!
— Seven Machina Rasmussen (@toomanyspectra) April 22, 2024
Other retrograde motion is real
Astronomers also use the word retrograde to describe true backward motion among planets and moons.
Venus, for example, rotates or spins on its axis in the opposite direction from every other planet in the solar system. If the clouds ever parted, hypothetical Venusians would see the sun rise in the west and set in the east. Astronomers would say that Venus rotates in a retrograde manner.
Some moons also have retrograde orbits around their planets. In other words, most of the large moons orbit in the same direction that their planet spins … but not Triton, for example, the largest moon of Neptune. It orbits opposite the direction of Neptune’s spin.
Among the smaller asteroid-like moons that swarm about the giant planets, many have retrograde orbits.
It’s the same word: retrograde. But now there’s no illusion. Whether speaking of a planet’s rotation – or its orbit – if it’s opposite what you’d expect, astronomers call it retrograde.
A photomosaic from Voyager 2 of Neptune’s largest moon, Triton. The moon orbits Neptune opposite the direction that the planet rotates. Does this mean that Triton came from the Kuiper Belt and was eventually captured by the ice giant? Image via NASA.
How does it happen?
According to modern astronomers, a true retrograde orbit for an orbiting moon most likely stems from a capture. Triton, for example, might have come out of the Kuiper Belt, the region of icy debris beyond Neptune. Perhaps a collision in the belt sent Triton careening inward toward the sun. A close encounter with Neptune could have slowed it down, forcing it to settle into a backward orbit.
In past decades, astronomers have also discovered planets in distant solar systems with retrograde orbits. These exoplanets orbit their suns in the opposite direction from how the star rotates.
It’s puzzling, because planets form out of debris disks that orbit young stars. And those orbiting disks share the star’s rotation. So how does a planet end up with a true backward orbit? The only way – some astronomers believe – is either by a near-collision with another planet, or if another star once passed too close to the system.
Either way, close encounters can disrupt the orbits of planets and set them on a backward path!
Bottom line: What is retrograde motion? See an image that appears to show the moon moving backwards! An explanation, and more bizarre examples, here.
This interactive map compares the Mercator projection versus the Equal Earth projection. Use the slide bar to compare the 2 maps. Image via EqualEarthMap.app.
The best map of Earth is a globe. Any flat map will distort some areas. For years, criticism has been leveled at the widely used Mercator projection map for its noticeable distortions. And on September 4, 2026, the U.N. General Assembly voted 164 to 1 – with six abstentions – to encourage the use of equal-area maps – such as the Equal Earth projection – in certain situations over the Mercator projection map.
The ruling does not change any borders or ban the use of the Mercator map. It simply recommends using an equal earth map in situations where seeing areas of Earth in true proportion are useful.
The Mercator map’s biggest drawback is that land closest to the equator looks smaller than it should, while land nearer to the poles looks huge. It’s why people have such a distorted view of the size of Greenland, for instance. And an equal-area Earth map is still a two-dimensional map, so it has its own drawbacks. For example, equal-area maps will distort shapes and angles near the poles.
So what exactly is an equal-area map of Earth?
The best representation of Earth is, of course, a globe. But flat images on pages and screens make globes not always the most practical option. Video by McZerrill/ Pixabay.
What is an Equal Earth projection map?
The Equal Earth map is a specific map invented in 2018. Its goal is to keep the relative size of land masses. Mercator maps are useful because they preserve angles that are important in marine navigation. Equal Earth maps are useful for comparing different regions of the world. As NewWorldMap.org explains:
Equal Earth is a modern equal-area projection designed to keep the relative sizes of countries and continents correct without giving the world an unfamiliar, severely stretched outline.
View larger. | This is an Equal Earth map. Note how land near the equator, such as Africa, looks larger than on a Mercator projection map (below). Then compare the sizes of Greenland. Image via Tom Patterson/ Wikimedia Commons.This is a Mercator projection map. Note how areas near the poles seem outsized, while areas near the equator appear small in comparison. Image via Wikimedia Commons.
What will you see differently?
Africa will likely look larger on the Equal Earth map than you are used to seeing on other flat maps. But if you compare the Equal Earth map to the view of Africa on the spinning globe, you will see they are more in harmony. As a specific example, one of the countries on the equator in Africa – Somalia, which curves around the Horn of Africa – is about the size of the U.S. East Coast.
Over in South America, you can see that Brazil also sits on the equator. The Equal Earth map more accurately shows the large size of Brazil. In fact, Brazil is so large that the country’s northernmost point is closer to Canada than it is to Brazil’s southernmost point.
Note the size of Greenland on the Equal Earth map. On Mercator projection maps, Greenland can look as large as Africa.
Africa is much larger than you are used to seeing on a Mercator projection map. Its length is equal to Russia’s width. The U.S. can fit comfortably inside Northern Africa. Image via Statista.
What other differences do you see between the Equal Earth and Mercator projection maps? Share in the comments below.
Bottom line: Everyone is familiar with the Mercator map, a flattened view of Earth. But what is the Equal Earth projection map, and how does it compare?
This interactive map compares the Mercator projection versus the Equal Earth projection. Use the slide bar to compare the 2 maps. Image via EqualEarthMap.app.
The best map of Earth is a globe. Any flat map will distort some areas. For years, criticism has been leveled at the widely used Mercator projection map for its noticeable distortions. And on September 4, 2026, the U.N. General Assembly voted 164 to 1 – with six abstentions – to encourage the use of equal-area maps – such as the Equal Earth projection – in certain situations over the Mercator projection map.
The ruling does not change any borders or ban the use of the Mercator map. It simply recommends using an equal earth map in situations where seeing areas of Earth in true proportion are useful.
The Mercator map’s biggest drawback is that land closest to the equator looks smaller than it should, while land nearer to the poles looks huge. It’s why people have such a distorted view of the size of Greenland, for instance. And an equal-area Earth map is still a two-dimensional map, so it has its own drawbacks. For example, equal-area maps will distort shapes and angles near the poles.
So what exactly is an equal-area map of Earth?
The best representation of Earth is, of course, a globe. But flat images on pages and screens make globes not always the most practical option. Video by McZerrill/ Pixabay.
What is an Equal Earth projection map?
The Equal Earth map is a specific map invented in 2018. Its goal is to keep the relative size of land masses. Mercator maps are useful because they preserve angles that are important in marine navigation. Equal Earth maps are useful for comparing different regions of the world. As NewWorldMap.org explains:
Equal Earth is a modern equal-area projection designed to keep the relative sizes of countries and continents correct without giving the world an unfamiliar, severely stretched outline.
View larger. | This is an Equal Earth map. Note how land near the equator, such as Africa, looks larger than on a Mercator projection map (below). Then compare the sizes of Greenland. Image via Tom Patterson/ Wikimedia Commons.This is a Mercator projection map. Note how areas near the poles seem outsized, while areas near the equator appear small in comparison. Image via Wikimedia Commons.
What will you see differently?
Africa will likely look larger on the Equal Earth map than you are used to seeing on other flat maps. But if you compare the Equal Earth map to the view of Africa on the spinning globe, you will see they are more in harmony. As a specific example, one of the countries on the equator in Africa – Somalia, which curves around the Horn of Africa – is about the size of the U.S. East Coast.
Over in South America, you can see that Brazil also sits on the equator. The Equal Earth map more accurately shows the large size of Brazil. In fact, Brazil is so large that the country’s northernmost point is closer to Canada than it is to Brazil’s southernmost point.
Note the size of Greenland on the Equal Earth map. On Mercator projection maps, Greenland can look as large as Africa.
Africa is much larger than you are used to seeing on a Mercator projection map. Its length is equal to Russia’s width. The U.S. can fit comfortably inside Northern Africa. Image via Statista.
What other differences do you see between the Equal Earth and Mercator projection maps? Share in the comments below.
Bottom line: Everyone is familiar with the Mercator map, a flattened view of Earth. But what is the Equal Earth projection map, and how does it compare?
The house-shaped constellation Cepheus the King lies in the northern sky near the constellation Cassiopeia and the north pole star, Polaris. And one of its stars, Delta Cephei, was a key to determining distances in the universe.
Delta Cephei is a pulsating star
Delta Cephei, in the constellation Cepheus the King, is a variable star that changes in brightness with clock-like precision. In fact, it doubles in brightness and fades back to minimum brightness every 5.366 days. So with careful observation under a dark sky, you can see this star change in brightness over several days. Delta Cephei, and other stars like it, are important players in establishing the distance scale of our galaxy … and our universe.
Delta Cephei itself looms large in the history of astronomy. An entire class of supergiant stars called Cepheid variables is named in this star’s honor.
#TBT to 1912 when Henrietta Swan Leavitt published ground-breaking observations of Cepheid variable stars. They were key to the discovery by Edwin Hubble that the Andromeda “nebula” is a galaxy like our own Milky Way. Learn more: https://t.co/5oDsiPWtiJpic.twitter.com/KXeP6XHgin
Cepheid variable stars, also called Cepheids, dependably change their brightnesses over regular intervals ranging from a few days to a few weeks. In 1912, astronomer Henrietta Leavitt discovered that the star’s periodic change in brightness in our sky was directly related to its intrinsic brightness (or actual luminosity). And she found that the longer the brightness pulsation cycle, the greater the intrinsic brightness of the star in reality. Sometimes this Cepheid period-luminosity relationship is called the Leavitt law.
Why are these stars varying in brightness? It’s thought they vary because they expand (get brighter) and then contract (get fainter) in a regular way.
A light curve plot of the changes in brightness in Delta Cephei. The Y axis (upward) is brightness in units of magnitude, and the X axis (across) is time. At the bottom, the two lowest points are when the star is at its minimum brightness. The time it takes from one minimum to the other is 5.366 days. Image via ThomasK Vbg/ Wikimedia Commons.
Cepheids help measure cosmic distances
The regularity of Cepheids’ brightening and dimming is a powerful tool in astronomy. It lets astronomers probe distances across vast space.
The surest way to measure star distances is with stellar parallax. But, for the parallax method to work with Earth-based telescopes, the stars have to be relatively nearby (within about 300 light-years) of Earth. Luckily, in recent years, astronomers have been able to make direct parallax measurements of more distant stars – up to tens of thousands light-years away – thanks to space-based telescopes such as Gaia.
Still, the problem remains. How can we find the distance to stars that are too far away to give us a reliable distance measurement using parallax? Suppose you measured the distance to a nearby Cepheid star using the parallax method. Then suppose you watched its pulsations, which you know are correlated with the star’s intrinsic – real – brightness. Then you know both its distance and how bright the star looks at that distance.
Armed with this information, you can then look farther out in the universe toward more distant Cepheids, those too far for parallax measurements. You can measure the apparent brightness and pulsation rate of such a star. And with a few simple calculations, you can then find the distance to it.
Therefore, astronomers use Cepheid variable stars to measure distances across space. For this reason, they’re known as standard candles by astronomers.
Edwin Hubble used Cepheids to expand our known universe
In 1924, the astronomer Edwin Hubble used Cepheids to determine that the then-called Andromeda nebula is not a nebula after all, but a giant galaxy lying beyond our Milky Way. Indeed, it released us from the confines of a single galaxy and introduced us to the vast universe we know today. This work in understanding the size of the universe is sometimes called the cosmic distance ladder.
And the work continues today, not just with Cepheids but also with other astronomical objects and phenomena.
An example of the period-luminosity relationship of Cepheids in the Large Magellanic Cloud, a satellite galaxy of our Milky Way. The plot shows the intrinsic brightness of stars vs. their pulsation periods. Each star, represented by a dot in the plot, is roughly the same distance from us. Henrietta Leavitt discovered, as illustrated in this plot, that the longer the brightness pulsation cycle, the greater the intrinsic brightness of the star. Image via Dbenford/ Wikimedia Commons.
Cepheids in other galaxies
Distance determinations using Cepheids in other galaxies, as well as other techniques, are an active area of research in astronomy. And astronomers are constantly improving distance accuracies to further constrain the value of the Hubble constant that indicates the expansion rate of the universe.
Cepheids have been observed as far away as 100 million light-years in the galaxy NGC 4603, by the Hubble Space Telescope. However, measuring them at distances of 30 million light-years and farther is difficult because it’s hard to isolate Cepheids from their neighboring stars. At such distances, astronomers transition to other methods to determine distances, such as observing type 1a supernovae.
View larger. | A star map of Cepheus, showing Delta Cephei, as well as Epsilon and Zeta Cephei, at the bottom left corner of the constellation. Image via IAU/ Sky & Telescope/ Wikimedia Commons.
How to spot Delta Cephei in the night sky
The original Cepheid, Delta Cephei, is circumpolar – always above the horizon – in the northern half of the United States (north of about 40 degrees north latitude).
Even so, Delta Cephei is much easier to see when it’s high in the northern sky on autumn and winter evenings. So if you’re far enough north, you can find the constellation Cepheus using the Big Dipper. First, locate the Big Dipper “pointer stars” to draw an imaginary line to Polaris, the North Star. Then jump beyond Polaris by a fist-width to land on Cepheus.
You’ll see the constellation Cepheus the King close to his wife, Cassiopeia the Queen, her signature W or M-shaped figure of stars making her the flashier of the two constellations. They’re high in your northern sky on November and December evenings.
For viewers in the Southern Hemisphere, Cepheus can be viewed as far south as -10 degrees southern latitude. Parts of Cepheus – including Delta Cephei – can be viewed low on the northern horizon from around -31 degrees southern latitude.
Charts for Delta Cephei
View larger. | If you’re not able to see the Big Dipper, try using the distinctive W-shaped Cassiopeia to locate the house-shaped Cepheus. The open side of the “W” faces the “roof” of Cepheus. Once you locate the “roof,” look for a rectangle pattern of 4 stars connected to it. Image via Stellarium.View larger. | A larger view of Cepheus, showing the Cepheid variable Delta Cepheid (circled) near two other stars, Zeta and Epsilon Cephei. Delta Cephei displays about a two-fold change in brightness (0.23 visual magnitudes) every 5.366 days, ranging from a visual magnitude of 3.48 at its brightest to 4.37 at its faintest. Zeta and Epsilon Cephei are useful comparison stars for noting the changes in brightness of Delta Cephei from one night to the next. Zeta Cephei has a visual magnitude of 3.35, which is close to the maximum brightness of Delta Cephei. Epsilon Cephei has a visual magnitude of 4.15, which is close to the minimum brightness of Delta Cephei. Image via Stellarium.
How to watch Delta Cephei vary in brightness
How to watch Delta Cephei vary in brightness? The real answer to that question is time and patience. But two stars lodging near Delta Cephei on the sky’s dome – Epsilon Cephei and Zeta Cephei – can help. They match the low and high ends of Delta Cephei’s brightness scale, respectively. So, those two stars should help you watch Delta Cephei change.
Using the charts above, locate the stars Epsilon and Zeta Cephei. At its faintest, Delta Cephei is as dim as the fainter star, Epsilon Cephei. At its brightest, Delta Cephei matches the brightness of the brighter star, Zeta Cephei.
Have fun!
View larger. | Astrophotographer Alan Dyer captured this image of Delta Cephei (center), with the Wizard Nebula on its left, and the nebula Sharpless 2-135 on its right. The orangish star on the far right is Zeta Cephei. Image via Alan Dyer/ AmazingSky.com/ Flickr. Used with permission.
Bottom line: Delta Cephei is an inconspicuous variable star in the northern constellation Cepheus the King. This important star helped establish the cosmic distance scale.
The house-shaped constellation Cepheus the King lies in the northern sky near the constellation Cassiopeia and the north pole star, Polaris. And one of its stars, Delta Cephei, was a key to determining distances in the universe.
Delta Cephei is a pulsating star
Delta Cephei, in the constellation Cepheus the King, is a variable star that changes in brightness with clock-like precision. In fact, it doubles in brightness and fades back to minimum brightness every 5.366 days. So with careful observation under a dark sky, you can see this star change in brightness over several days. Delta Cephei, and other stars like it, are important players in establishing the distance scale of our galaxy … and our universe.
Delta Cephei itself looms large in the history of astronomy. An entire class of supergiant stars called Cepheid variables is named in this star’s honor.
#TBT to 1912 when Henrietta Swan Leavitt published ground-breaking observations of Cepheid variable stars. They were key to the discovery by Edwin Hubble that the Andromeda “nebula” is a galaxy like our own Milky Way. Learn more: https://t.co/5oDsiPWtiJpic.twitter.com/KXeP6XHgin
Cepheid variable stars, also called Cepheids, dependably change their brightnesses over regular intervals ranging from a few days to a few weeks. In 1912, astronomer Henrietta Leavitt discovered that the star’s periodic change in brightness in our sky was directly related to its intrinsic brightness (or actual luminosity). And she found that the longer the brightness pulsation cycle, the greater the intrinsic brightness of the star in reality. Sometimes this Cepheid period-luminosity relationship is called the Leavitt law.
Why are these stars varying in brightness? It’s thought they vary because they expand (get brighter) and then contract (get fainter) in a regular way.
A light curve plot of the changes in brightness in Delta Cephei. The Y axis (upward) is brightness in units of magnitude, and the X axis (across) is time. At the bottom, the two lowest points are when the star is at its minimum brightness. The time it takes from one minimum to the other is 5.366 days. Image via ThomasK Vbg/ Wikimedia Commons.
Cepheids help measure cosmic distances
The regularity of Cepheids’ brightening and dimming is a powerful tool in astronomy. It lets astronomers probe distances across vast space.
The surest way to measure star distances is with stellar parallax. But, for the parallax method to work with Earth-based telescopes, the stars have to be relatively nearby (within about 300 light-years) of Earth. Luckily, in recent years, astronomers have been able to make direct parallax measurements of more distant stars – up to tens of thousands light-years away – thanks to space-based telescopes such as Gaia.
Still, the problem remains. How can we find the distance to stars that are too far away to give us a reliable distance measurement using parallax? Suppose you measured the distance to a nearby Cepheid star using the parallax method. Then suppose you watched its pulsations, which you know are correlated with the star’s intrinsic – real – brightness. Then you know both its distance and how bright the star looks at that distance.
Armed with this information, you can then look farther out in the universe toward more distant Cepheids, those too far for parallax measurements. You can measure the apparent brightness and pulsation rate of such a star. And with a few simple calculations, you can then find the distance to it.
Therefore, astronomers use Cepheid variable stars to measure distances across space. For this reason, they’re known as standard candles by astronomers.
Edwin Hubble used Cepheids to expand our known universe
In 1924, the astronomer Edwin Hubble used Cepheids to determine that the then-called Andromeda nebula is not a nebula after all, but a giant galaxy lying beyond our Milky Way. Indeed, it released us from the confines of a single galaxy and introduced us to the vast universe we know today. This work in understanding the size of the universe is sometimes called the cosmic distance ladder.
And the work continues today, not just with Cepheids but also with other astronomical objects and phenomena.
An example of the period-luminosity relationship of Cepheids in the Large Magellanic Cloud, a satellite galaxy of our Milky Way. The plot shows the intrinsic brightness of stars vs. their pulsation periods. Each star, represented by a dot in the plot, is roughly the same distance from us. Henrietta Leavitt discovered, as illustrated in this plot, that the longer the brightness pulsation cycle, the greater the intrinsic brightness of the star. Image via Dbenford/ Wikimedia Commons.
Cepheids in other galaxies
Distance determinations using Cepheids in other galaxies, as well as other techniques, are an active area of research in astronomy. And astronomers are constantly improving distance accuracies to further constrain the value of the Hubble constant that indicates the expansion rate of the universe.
Cepheids have been observed as far away as 100 million light-years in the galaxy NGC 4603, by the Hubble Space Telescope. However, measuring them at distances of 30 million light-years and farther is difficult because it’s hard to isolate Cepheids from their neighboring stars. At such distances, astronomers transition to other methods to determine distances, such as observing type 1a supernovae.
View larger. | A star map of Cepheus, showing Delta Cephei, as well as Epsilon and Zeta Cephei, at the bottom left corner of the constellation. Image via IAU/ Sky & Telescope/ Wikimedia Commons.
How to spot Delta Cephei in the night sky
The original Cepheid, Delta Cephei, is circumpolar – always above the horizon – in the northern half of the United States (north of about 40 degrees north latitude).
Even so, Delta Cephei is much easier to see when it’s high in the northern sky on autumn and winter evenings. So if you’re far enough north, you can find the constellation Cepheus using the Big Dipper. First, locate the Big Dipper “pointer stars” to draw an imaginary line to Polaris, the North Star. Then jump beyond Polaris by a fist-width to land on Cepheus.
You’ll see the constellation Cepheus the King close to his wife, Cassiopeia the Queen, her signature W or M-shaped figure of stars making her the flashier of the two constellations. They’re high in your northern sky on November and December evenings.
For viewers in the Southern Hemisphere, Cepheus can be viewed as far south as -10 degrees southern latitude. Parts of Cepheus – including Delta Cephei – can be viewed low on the northern horizon from around -31 degrees southern latitude.
Charts for Delta Cephei
View larger. | If you’re not able to see the Big Dipper, try using the distinctive W-shaped Cassiopeia to locate the house-shaped Cepheus. The open side of the “W” faces the “roof” of Cepheus. Once you locate the “roof,” look for a rectangle pattern of 4 stars connected to it. Image via Stellarium.View larger. | A larger view of Cepheus, showing the Cepheid variable Delta Cepheid (circled) near two other stars, Zeta and Epsilon Cephei. Delta Cephei displays about a two-fold change in brightness (0.23 visual magnitudes) every 5.366 days, ranging from a visual magnitude of 3.48 at its brightest to 4.37 at its faintest. Zeta and Epsilon Cephei are useful comparison stars for noting the changes in brightness of Delta Cephei from one night to the next. Zeta Cephei has a visual magnitude of 3.35, which is close to the maximum brightness of Delta Cephei. Epsilon Cephei has a visual magnitude of 4.15, which is close to the minimum brightness of Delta Cephei. Image via Stellarium.
How to watch Delta Cephei vary in brightness
How to watch Delta Cephei vary in brightness? The real answer to that question is time and patience. But two stars lodging near Delta Cephei on the sky’s dome – Epsilon Cephei and Zeta Cephei – can help. They match the low and high ends of Delta Cephei’s brightness scale, respectively. So, those two stars should help you watch Delta Cephei change.
Using the charts above, locate the stars Epsilon and Zeta Cephei. At its faintest, Delta Cephei is as dim as the fainter star, Epsilon Cephei. At its brightest, Delta Cephei matches the brightness of the brighter star, Zeta Cephei.
Have fun!
View larger. | Astrophotographer Alan Dyer captured this image of Delta Cephei (center), with the Wizard Nebula on its left, and the nebula Sharpless 2-135 on its right. The orangish star on the far right is Zeta Cephei. Image via Alan Dyer/ AmazingSky.com/ Flickr. Used with permission.
Bottom line: Delta Cephei is an inconspicuous variable star in the northern constellation Cepheus the King. This important star helped establish the cosmic distance scale.
As summer turns to fall in North America, millions of hummingbirds migrate south to warmer climes. More than a dozen species of tiny hummers are on the move through the end of October. Flying from as far north as Canada, they can end up as far south as Central America. The colorful daredevil fliers need a lot of sweet nectar – natural or artificial – to fuel the journey. Ornithologist Sheri Williamson joins EarthSky’s Dave Adalian to talk about best practices for interacting with these fascinating seasonal visitors. Watch here or at YouTube. And read more about fall hummingbird migration below.
Hummingbirds are on the move. As summer winds down across North America, many hummingbirds begin their southward migration. The mass movement is typically in swing by late August – though the males may make an earlier start – and it continues into late October and beyond.
During those usually temperate months, the skies over every U.S. state and Canadian province become a nectar-fueled highway for tiny bejeweled avians. And they’ll be making a lot of stops at colorful flowering plants and bird feeders along the way.
A long and tiring journey for these miniscule flyers
For some of these small wanderers, the journey will take them hundreds or even thousands of miles from the wilds of Canada, south across the United States and finally into Mexico and Central America. A few of the most daring hummers will take a perilous nonstop flight across the Gulf of Mexico to reach their winter homes.
The small birds turn up almost everywhere in North America. While some locations have hummers all year, for most North American locations the stay is only seasonal.
According to research published in 2016, an individual ruby-throated hummingbird was recorded traveling 3,082 miles (4,960 km) during its fall migration. Ruby-throated hummers on average migrate around 1,400 miles (2,250 km) each way during their flight to better weather.
They perform most of that journey in short hops with lingering stopovers to eat. But when the birds reach the Gulf of Mexico, they must make the approximately 600-mile (1,000-km) water crossing in a single flight. Only a few of the ruby-throated hummers are brave or strong enough to try the route in autumn. The rest typically follow the Texas-Mexico coastline south around the Gulf.
3 avenues open for fall hummingbird migration
Besides the ruby-throated hummer, there are several other common hummingbird species. Most, but not all, of those species migrate with the seasons. In general, North America can be divided into three distinct migratory pathways.
Eastern States: Ruby-throated hummingbirds are found only east of the Rocky Mountains. They’re seen throughout that region, and for most of the eastern half of North America, the ruby-throated hummer is the only species commonly seen.
Middle States: However, the center of the continent, an area from about Central Texas west to the Rockies, is home to several species: the black-chinned, the rufous, the broad-tail, the Calliope and Allen’s hummingbirds. The Calliope’s range is somewhat northerly.
Western States: The area west of the Rocky Mountains is also home to a variety of hummingbirds. Anna’s hummingbirds are year-long residents that don’t migrate. Sharing their range are the Allen’s, the black-chinned, the Costa’s, the blue-throated, the rufous and the broad-tailed hummingbirds.
Watch a live cam of hummingbirds visiting feeders. Right now, the fall hummingbird migration is in progress across North America. Read on for info on how you can help these weary travelers.
Humans can lend traveling hummers a helping hand
According to JourneyNorth.com, hummingbirds double their weight as they prepare for their long-distance journeys southward. To do that, they need abundant food sources. They also need habitat. Humans can provide both, says migration expert Julian Avery of Penn State:
Studies show that providing food has myriad effects on birds’ decisions, behaviors and reproduction. One significant finding is that winter bird feeding increases individual survival rates, can encourage birds to lay eggs earlier in the year, and can also improve nestling survival.
The most popular way of attracting hummers is using hummingbird feeders. HummingbirdCentral.com offers tips for placing them and a sugar-water recipe that mimics the calorie content of nectar. They also offer advice for avoiding pathogens and for keeping away unwanted visitors, like bees.
Costa’s hummingbirds are frequent visitors at feeders in Arizona and southern California. Image via Julian Avery/ The Conversation.
Native plant gardens boost success during fall hummingbird migration
The more ecologically minded might want to fill their yards and gardens with hummingbird-friendly plants. The right landscaping can make a yard attractive to hummers, but it depends on what region. The Missouri Prairie Association offers tips for the middle region of the country at GrowNative.org.
The California Native Plant Society has hummer-friendly garden advice for those west of the Rockies. Those living in the eastern half of the country will find appropriate hummingbird plants for the garden at Penn State’s Center for Pollinator Research.
In general, the tiny travelers are attracted to plants with red, orange and yellow flowers. Nectar is a prime source of calories for hummers. But they are also omnivores who consume any insect they can catch. Any plant that provides home for bugs will also provide shelter and food for hummingbirds.
There are some issues to consider when feeding wild birds. In an article from The Conversation, Avery discusses them in depth:
There is still much to learn about the risks and benefits of feeding birds, particularly through large integrated national citizen science networks like Project FeederWatch. But we now have enough information to promote healthy interactions that can inspire future generations to care about conservation.
In addition to using Project FeederWatch, seasonal birdwatchers can report their sightings to JourneyNorth.org. And, for the spring migration, you can also track via HummingbirdCentral.com.
Bottom line: The fall hummingbird migration in North America typically lasts from August through October. You can spot the tiny birds in every U.S. state and Canadian province as they travel south.
As summer turns to fall in North America, millions of hummingbirds migrate south to warmer climes. More than a dozen species of tiny hummers are on the move through the end of October. Flying from as far north as Canada, they can end up as far south as Central America. The colorful daredevil fliers need a lot of sweet nectar – natural or artificial – to fuel the journey. Ornithologist Sheri Williamson joins EarthSky’s Dave Adalian to talk about best practices for interacting with these fascinating seasonal visitors. Watch here or at YouTube. And read more about fall hummingbird migration below.
Hummingbirds are on the move. As summer winds down across North America, many hummingbirds begin their southward migration. The mass movement is typically in swing by late August – though the males may make an earlier start – and it continues into late October and beyond.
During those usually temperate months, the skies over every U.S. state and Canadian province become a nectar-fueled highway for tiny bejeweled avians. And they’ll be making a lot of stops at colorful flowering plants and bird feeders along the way.
A long and tiring journey for these miniscule flyers
For some of these small wanderers, the journey will take them hundreds or even thousands of miles from the wilds of Canada, south across the United States and finally into Mexico and Central America. A few of the most daring hummers will take a perilous nonstop flight across the Gulf of Mexico to reach their winter homes.
The small birds turn up almost everywhere in North America. While some locations have hummers all year, for most North American locations the stay is only seasonal.
According to research published in 2016, an individual ruby-throated hummingbird was recorded traveling 3,082 miles (4,960 km) during its fall migration. Ruby-throated hummers on average migrate around 1,400 miles (2,250 km) each way during their flight to better weather.
They perform most of that journey in short hops with lingering stopovers to eat. But when the birds reach the Gulf of Mexico, they must make the approximately 600-mile (1,000-km) water crossing in a single flight. Only a few of the ruby-throated hummers are brave or strong enough to try the route in autumn. The rest typically follow the Texas-Mexico coastline south around the Gulf.
3 avenues open for fall hummingbird migration
Besides the ruby-throated hummer, there are several other common hummingbird species. Most, but not all, of those species migrate with the seasons. In general, North America can be divided into three distinct migratory pathways.
Eastern States: Ruby-throated hummingbirds are found only east of the Rocky Mountains. They’re seen throughout that region, and for most of the eastern half of North America, the ruby-throated hummer is the only species commonly seen.
Middle States: However, the center of the continent, an area from about Central Texas west to the Rockies, is home to several species: the black-chinned, the rufous, the broad-tail, the Calliope and Allen’s hummingbirds. The Calliope’s range is somewhat northerly.
Western States: The area west of the Rocky Mountains is also home to a variety of hummingbirds. Anna’s hummingbirds are year-long residents that don’t migrate. Sharing their range are the Allen’s, the black-chinned, the Costa’s, the blue-throated, the rufous and the broad-tailed hummingbirds.
Watch a live cam of hummingbirds visiting feeders. Right now, the fall hummingbird migration is in progress across North America. Read on for info on how you can help these weary travelers.
Humans can lend traveling hummers a helping hand
According to JourneyNorth.com, hummingbirds double their weight as they prepare for their long-distance journeys southward. To do that, they need abundant food sources. They also need habitat. Humans can provide both, says migration expert Julian Avery of Penn State:
Studies show that providing food has myriad effects on birds’ decisions, behaviors and reproduction. One significant finding is that winter bird feeding increases individual survival rates, can encourage birds to lay eggs earlier in the year, and can also improve nestling survival.
The most popular way of attracting hummers is using hummingbird feeders. HummingbirdCentral.com offers tips for placing them and a sugar-water recipe that mimics the calorie content of nectar. They also offer advice for avoiding pathogens and for keeping away unwanted visitors, like bees.
Costa’s hummingbirds are frequent visitors at feeders in Arizona and southern California. Image via Julian Avery/ The Conversation.
Native plant gardens boost success during fall hummingbird migration
The more ecologically minded might want to fill their yards and gardens with hummingbird-friendly plants. The right landscaping can make a yard attractive to hummers, but it depends on what region. The Missouri Prairie Association offers tips for the middle region of the country at GrowNative.org.
The California Native Plant Society has hummer-friendly garden advice for those west of the Rockies. Those living in the eastern half of the country will find appropriate hummingbird plants for the garden at Penn State’s Center for Pollinator Research.
In general, the tiny travelers are attracted to plants with red, orange and yellow flowers. Nectar is a prime source of calories for hummers. But they are also omnivores who consume any insect they can catch. Any plant that provides home for bugs will also provide shelter and food for hummingbirds.
There are some issues to consider when feeding wild birds. In an article from The Conversation, Avery discusses them in depth:
There is still much to learn about the risks and benefits of feeding birds, particularly through large integrated national citizen science networks like Project FeederWatch. But we now have enough information to promote healthy interactions that can inspire future generations to care about conservation.
In addition to using Project FeederWatch, seasonal birdwatchers can report their sightings to JourneyNorth.org. And, for the spring migration, you can also track via HummingbirdCentral.com.
Bottom line: The fall hummingbird migration in North America typically lasts from August through October. You can spot the tiny birds in every U.S. state and Canadian province as they travel south.
Sirius is the sky’s brightest star. You can always be sure you’re looking at the correct bright star by drawing a line from Orion’s Belt to Sirius. And from the Southern Hemisphere, turn the chart upside down.
Orion’s Belt points to Sirius
It’s one of the neatest tricks in all the heavens: Orion’s Belt points to Sirius, the sky’s brightest star.
On September mornings, you’ll find both Orion the Hunter and the very bright star Sirius in the eastern part of the sky before dawn. And before you know it, they’ll be shifting into the evening sky. So identify them now, and enjoy them for months to come.
Sometimes there are bright planets in the same region that might outshine even Sirius. For example, in September 2026, Jupiter is also in the morning sky and definitely outshines our brightest star. What’s more, bright planets often adorn the evening sky during the northern winter, when Orion and Sirius shine brightly. In these cases, how can you be sure the object you’re looking at is Sirius? The constellation Orion is your ticket. And no matter where you are, no matter what time of the year it is, Orion’s Belt always points to Sirius.
Flying into Orion’s Belt at 0.001c ?The hunter isn’t flat. It’s a real 3D region of space. (Upgraded animation!) #astronomy ?
Orion returned to the sky before dawn in late July and early August. Now in September, you can easily find this large constellation before sunup. Just look in the eastern part of the sky. You’ll easily notice Orion’s Belt, which consists of a short, straight row of three medium-bright stars.
And to find Sirius, draw a line through Orion’s Belt and extend that line toward the horizon. There, you’ll spot Sirius, the sky’s brightest star.
Sirius is in the constellation Canis Major the Greater Dog. Indeed, it’s often called the Dog Star.
View at EarthSky Community Photos. | Sergei Timofeevski shared this image from November 13, 2023. Sergei wrote: “The constellation Orion the Hunter and the star Sirius rising just above the eastern horizon in the Anza-Borrego Desert State Park, California.” Thank you, Sergei! And note bright Sirius is at the bottom, with Orion’s Belt pointing to it.
Bottom line: Use Orion’s Belt to find Sirius, the sky’s brightest star. In 2026, Jupiter is in the same region, outshining even Sirius.
Sirius is the sky’s brightest star. You can always be sure you’re looking at the correct bright star by drawing a line from Orion’s Belt to Sirius. And from the Southern Hemisphere, turn the chart upside down.
Orion’s Belt points to Sirius
It’s one of the neatest tricks in all the heavens: Orion’s Belt points to Sirius, the sky’s brightest star.
On September mornings, you’ll find both Orion the Hunter and the very bright star Sirius in the eastern part of the sky before dawn. And before you know it, they’ll be shifting into the evening sky. So identify them now, and enjoy them for months to come.
Sometimes there are bright planets in the same region that might outshine even Sirius. For example, in September 2026, Jupiter is also in the morning sky and definitely outshines our brightest star. What’s more, bright planets often adorn the evening sky during the northern winter, when Orion and Sirius shine brightly. In these cases, how can you be sure the object you’re looking at is Sirius? The constellation Orion is your ticket. And no matter where you are, no matter what time of the year it is, Orion’s Belt always points to Sirius.
Flying into Orion’s Belt at 0.001c ?The hunter isn’t flat. It’s a real 3D region of space. (Upgraded animation!) #astronomy ?
Orion returned to the sky before dawn in late July and early August. Now in September, you can easily find this large constellation before sunup. Just look in the eastern part of the sky. You’ll easily notice Orion’s Belt, which consists of a short, straight row of three medium-bright stars.
And to find Sirius, draw a line through Orion’s Belt and extend that line toward the horizon. There, you’ll spot Sirius, the sky’s brightest star.
Sirius is in the constellation Canis Major the Greater Dog. Indeed, it’s often called the Dog Star.
View at EarthSky Community Photos. | Sergei Timofeevski shared this image from November 13, 2023. Sergei wrote: “The constellation Orion the Hunter and the star Sirius rising just above the eastern horizon in the Anza-Borrego Desert State Park, California.” Thank you, Sergei! And note bright Sirius is at the bottom, with Orion’s Belt pointing to it.
Bottom line: Use Orion’s Belt to find Sirius, the sky’s brightest star. In 2026, Jupiter is in the same region, outshining even Sirius.
Have you ever wondered how many stars you can see in a dark sky?
How many stars can you see?
Imagine you’re under a dark sky far away from city lights, on a night with no moon, no clouds and no haze. How many stars could you see with your unaided eye? There’s really no definitive answer to this question, but astronomers use different numbers as theoretical estimates.
Considering all the stars visible in all directions around Earth, the upper end on the estimates is close to 10,000 visible stars. Here’s how one source, astronomytrek.com, came up with that number:
The brighter the star, the lower the apparent magnitude value assigned to it, with the most luminous given a negative number. In total there are 22 stars with magnitudes of between -1 and 1, making them the night sky’s brightest stars. In the meantime, there are 71 stars of 2nd magnitude, 190 stars of 3rd magnitude, 610 of 4th magnitude, 1,929 of 5th magnitude, and 5,946 of 6th magnitude. When we include another 3,150 stars at the limit of our visual acuity of magnitude +6.5, then this adds up to 9,096 stars that it is possible to see in the night sky from both the Northern and Southern Hemispheres with the unaided eye.
And there’s two hemispheres
But one person couldn’t see all those stars at once. For instance, in the Northern Hemisphere, many of the stars visible from the Southern Hemisphere will be hidden below your southern horizon. So, therefore, each hemisphere can only see about 5,000 stars. And, at any given time, half of Earth is in daylight. So only half the estimated number – perhaps 2,500 stars – would be visible from Earth’s night side. Plus, another fraction of those visible stars would be lost in the murk surrounding your horizon. That could bring you down to around 2,000, the most common number you’ll see for these estimates.
View at EarthSky Community Photos. | Jeremy Evans of California captured a Lyrid meteor zipping along the Milky way on April 22, 2025. Jeremy wrote: “Lyrids meteor shower, April 22nd at peak activity. It was a quiet shower this year. I had my camera going all night and only caught one meteor. This single frame is from an all-night 1,200 frame time lapse on my front deck, I’m very fortunate to live under dark Bortle 2 skies. The glow on the horizon is from the last quarter moon just before rising.” Thank you, Jeremy.
Factors that affect your seeing
Why can’t astronomers agree on the number of visible stars? It’s because we don’t all see the sky in the same way. And even under ideal conditions, there’s a fair amount of variation between how well people can see the stars. Some of the factors include the strength of your vision and your age. As you get older, your eyes become much less sensitive to faint light.
Plus, you have to take into account the brightness of your night sky. Even on a moonless night, the glow of lights from Earth’s surface brightens the sky.
Still, far from city lights – under absolutely perfect conditions of darkness and sky clarity – a young to middle-aged person with normal vision should be able to see thousands of stars.
The WyoAstro allsky camera recorded 2045 stars (see upper right) on the morning of August 20, 2026. This is approximately the same view an observer would see in a fairly dark sky. Image via WyoAstro allsky camera. Used with permission.
Bottom line: Have you ever wondered how many stars are visible on a given night? It depends on factors including how dark your sky is and what your age is.
Have you ever wondered how many stars you can see in a dark sky?
How many stars can you see?
Imagine you’re under a dark sky far away from city lights, on a night with no moon, no clouds and no haze. How many stars could you see with your unaided eye? There’s really no definitive answer to this question, but astronomers use different numbers as theoretical estimates.
Considering all the stars visible in all directions around Earth, the upper end on the estimates is close to 10,000 visible stars. Here’s how one source, astronomytrek.com, came up with that number:
The brighter the star, the lower the apparent magnitude value assigned to it, with the most luminous given a negative number. In total there are 22 stars with magnitudes of between -1 and 1, making them the night sky’s brightest stars. In the meantime, there are 71 stars of 2nd magnitude, 190 stars of 3rd magnitude, 610 of 4th magnitude, 1,929 of 5th magnitude, and 5,946 of 6th magnitude. When we include another 3,150 stars at the limit of our visual acuity of magnitude +6.5, then this adds up to 9,096 stars that it is possible to see in the night sky from both the Northern and Southern Hemispheres with the unaided eye.
And there’s two hemispheres
But one person couldn’t see all those stars at once. For instance, in the Northern Hemisphere, many of the stars visible from the Southern Hemisphere will be hidden below your southern horizon. So, therefore, each hemisphere can only see about 5,000 stars. And, at any given time, half of Earth is in daylight. So only half the estimated number – perhaps 2,500 stars – would be visible from Earth’s night side. Plus, another fraction of those visible stars would be lost in the murk surrounding your horizon. That could bring you down to around 2,000, the most common number you’ll see for these estimates.
View at EarthSky Community Photos. | Jeremy Evans of California captured a Lyrid meteor zipping along the Milky way on April 22, 2025. Jeremy wrote: “Lyrids meteor shower, April 22nd at peak activity. It was a quiet shower this year. I had my camera going all night and only caught one meteor. This single frame is from an all-night 1,200 frame time lapse on my front deck, I’m very fortunate to live under dark Bortle 2 skies. The glow on the horizon is from the last quarter moon just before rising.” Thank you, Jeremy.
Factors that affect your seeing
Why can’t astronomers agree on the number of visible stars? It’s because we don’t all see the sky in the same way. And even under ideal conditions, there’s a fair amount of variation between how well people can see the stars. Some of the factors include the strength of your vision and your age. As you get older, your eyes become much less sensitive to faint light.
Plus, you have to take into account the brightness of your night sky. Even on a moonless night, the glow of lights from Earth’s surface brightens the sky.
Still, far from city lights – under absolutely perfect conditions of darkness and sky clarity – a young to middle-aged person with normal vision should be able to see thousands of stars.
The WyoAstro allsky camera recorded 2045 stars (see upper right) on the morning of August 20, 2026. This is approximately the same view an observer would see in a fairly dark sky. Image via WyoAstro allsky camera. Used with permission.
Bottom line: Have you ever wondered how many stars are visible on a given night? It depends on factors including how dark your sky is and what your age is.
