Will the Blaze Star explode on March 27, 2025?

The Blaze Star isn’t one star but 2. It’s a binary system with a white dwarf and red giant. The Blaze Star’s white dwarf has built up material on its surface, siphoned off from the red giant star. Periodically, it “can’t take no more” and explodes, about every 80 years. Despite the powerful explosion, the dwarf itself remains intact. And once things settle down, the Blaze Star (T Corona Borealis) will begin the decades-long preparation for future cosmic fireworks. Image via NASA Goddard Scientific Visualization Studio.

A new estimate for the Blaze Star’s eruption

Will the Blaze Star finally explode on March 27, 2025? Or maybe it’s November 10, 2025? Or perhaps after that … Those are the predictions of Jean Schneider of the Paris Observatory, published in the Research Notes of the American Astronomical Society in October 2024.

Schneider came to his possible dates using a combination of the previous eruption dates and the orbital ephemeris of the binary system. While Schneider admits in his paper that no one can exactly predict the eruption, he is trying to predict eruption dates with a precision of a week or two. Will his predictions hold up? The only way to know for sure is to go out and observe Corona Borealis to see if a “new” star appears!

Waiting for the Blaze Star to go nova

Have you ever heard of the Blaze Star? It’s a star in the constellation Corona Borealis, the Northern Crown, that was supposed to go nova last year. Well, we’re still waiting. But when it finally does erupt, it’ll be a once-in-a-lifetime show in our night sky.

The eagerly awaited Blaze Star nova is a real opportunity for keen night sky observers to witness a “new star” in the sky … but only for a few days before it fades away again. Here’s more about why we’re still waiting on the Blaze Star. And about how you can see when it does finally erupt as a nova.

The 2025 EarthSky Lunar Calendar is now available! A unique and beautiful poster-sized calendar. Get yours today!

View at EarthSky Community Photos. | Paul Henkiel of Flagstaff, Arizona, captured this image on April 20, 2024. It’s the easy-to-spot C-shaped constellation Corona Borealis, the Northern Crown. The brightest star here is Alphecca, sometimes called the Jewel of the Crown. When the Blaze Star erupts, it’ll be approximately as bright as Alphecca. The Northern Crown will have 2 jewels! Thank you, Paul!

Why hasn’t it happened yet?

Predicting eruptions of stars is not an exact science. The Blaze Star (T Coronae Borealis) underwent two known eruptions recorded by astronomers. Those events were on May 12, 1866, and on February 9, 1946. Those eruptions were 80 years apart. So scientists thought that, in another 80 years, the star would erupt again. So, 80 years from 1946 would be 2026. Which raises the question: Why did astronomers think the eruption would happen in 2024?

Well, the star brightened and dimmed before its last eruption in 1946. And it has been brightening and dimming now as well, leading some to think the nova would happen sooner rather than later. But it appears as if later is more likely. And so we wait …

In the meantime, here’s how to find Corona Borealis and be ready to see it when the nova arrives.

Why will it go nova?

The Blaze Star isn’t one star but two. It’s a binary system with a white dwarf and a red giant. White dwarfs are stellar remnants, the exposed core of a sunlike star that shed its outer layers at the end of its main-sequence life. It’s a super-dense star with the mass of our sun but only the size of Earth.

Blaze Star’s white dwarf has built up material on its surface, siphoned off from the red giant star. Periodically, it “can’t take no more” and explodes, about every 80 years.

This is our best opportunity to see a nova with some warning. Plus we have great visual context from the surrounding C-shape of stars. So cross your fingers for good weather when it happens.

Artist’s concept of a red giant star and white dwarf star. A stream of material flows from the red giant to the white dwarf, eventually causing a runaway thermonuclear reaction on the white dwarf that will appear as a new star, or nova, in earthly skies. The constellation Corona Borealis the Northern Crown should have a nova appear from the Blaze Star approximately every 80 years. Image via NASA/ Goddard Space Flight Center.

Where to look to find the Blaze Star

The constellation Corona Borealis is back from a month hiding below the horizon. It rotates around Polaris just outside of what we traditionally think of as the circumpolar constellations. This mean it’s not visible all year round for much of the Northern Hemisphere.

The easy-to-find constellation looks distinctly like a backward C at this time of year. It lies between the bright star Arcturus and the squarish four-star shape of Hercules. Look east at the stars coming over the horizon before dawn. Find the bright orange star Arcturus. Then, to the bottom left of Arcturus is the backward C shape of Corona Borealis … unless there’s a guest star messing up the shape!

By the summer these constellations will be high in the sky again. You always need to spend some time dark-adapting your eyes before you see the constellations properly. Plus, binoculars would be a good idea. And you need to be ready to go when we get the news, as it will only be there for a couple of days.

Want to see the Blaze Star go nova? X marks the spot! Astronomers said an impending nova will give the constellation of the Northern Crown – Corona Borealis – an additional star that rivals its brightest star. Image via Chris Harvey/ Stellarium. Used with permission.

How bright will the Blaze Star be?

The actual explosion of the Blaze Star nova will likely dwarf any explosion you’ll ever see. But the star is far away. How bright will it get in our sky? Astronomers expect it to reach an apparent magnitude of 2. That’s a respectable brightness for a star. It’s conveniently comparable to the brightest star in the Northern Crown, the Jewel of the Crown, Alphecca. So, for a few days, the Northern Crown will have two jewels!

T Corana Borealis – the Blaze Star – also one of the most distant stars you’ll ever see. Alphecca is around 75 light-years away, while the Blaze Star is closer to 3,000 light-years away. So that gives you some perspective on the absolute magnitude (brightness) of this enormous blast. And since the light of this explosion has travelled for 3,000 years to get here, in relative terms the nova happened during the Bronze Age.

Remember that, when they are side-by-side with approximately the same brightness, the nova is 40 times farther away than Alphecca. Also, we are not seeing the two stars at the same moment in time. One we see as it was 75 years ago and the other we see as it was 3,000 years ago. It can be hard to get your head around that!

The nova will brighten the star by thousands of times, typically over just a few hours, and then take some days to fade away again. When it’s done, it will go back to its normal appearance.

Late at night in the spring, and high overhead during summer months, find the bright stars Vega and Arcturus. Then locate the constellations Hercules and Boötes. The semicircle of stars between them is the constellation Corona Borealis. Image via NASA.

Finding Corona Borealis, the Northern Crown

If you are not familiar with the Northern Crown, get out and have a look at it before this nova happens. And then, clouds willing, when it does erupt we can go out and see the C shape is harder to spot. Instead, the dominant feature will be two bright-ish stars, Alphecca (the brightest star in Corona Borealis), and the Blaze Star.

The Blaze Star is normally invisible to the unaided eye. On a regular day, it sits at around magnitude 10, making it only the 19th brightest star in the constellation. But as it undergoes a colossal outburst of energy, it will brighten.

Bottom line: We’re still waiting for the Blaze Star to go nova! Will it happen March 27? Here’s how to find Corona Borealis so you’re ready when it does happen.

Source: When will the Next T CrB Eruption Occur?

The post Will the Blaze Star explode on March 27, 2025? first appeared on EarthSky.

from EarthSky https://ift.tt/fhVQvKE

The Blaze Star isn’t one star but 2. It’s a binary system with a white dwarf and red giant. The Blaze Star’s white dwarf has built up material on its surface, siphoned off from the red giant star. Periodically, it “can’t take no more” and explodes, about every 80 years. Despite the powerful explosion, the dwarf itself remains intact. And once things settle down, the Blaze Star (T Corona Borealis) will begin the decades-long preparation for future cosmic fireworks. Image via NASA Goddard Scientific Visualization Studio.

A new estimate for the Blaze Star’s eruption

Will the Blaze Star finally explode on March 27, 2025? Or maybe it’s November 10, 2025? Or perhaps after that … Those are the predictions of Jean Schneider of the Paris Observatory, published in the Research Notes of the American Astronomical Society in October 2024.

Schneider came to his possible dates using a combination of the previous eruption dates and the orbital ephemeris of the binary system. While Schneider admits in his paper that no one can exactly predict the eruption, he is trying to predict eruption dates with a precision of a week or two. Will his predictions hold up? The only way to know for sure is to go out and observe Corona Borealis to see if a “new” star appears!

Waiting for the Blaze Star to go nova

Have you ever heard of the Blaze Star? It’s a star in the constellation Corona Borealis, the Northern Crown, that was supposed to go nova last year. Well, we’re still waiting. But when it finally does erupt, it’ll be a once-in-a-lifetime show in our night sky.

The eagerly awaited Blaze Star nova is a real opportunity for keen night sky observers to witness a “new star” in the sky … but only for a few days before it fades away again. Here’s more about why we’re still waiting on the Blaze Star. And about how you can see when it does finally erupt as a nova.

The 2025 EarthSky Lunar Calendar is now available! A unique and beautiful poster-sized calendar. Get yours today!

View at EarthSky Community Photos. | Paul Henkiel of Flagstaff, Arizona, captured this image on April 20, 2024. It’s the easy-to-spot C-shaped constellation Corona Borealis, the Northern Crown. The brightest star here is Alphecca, sometimes called the Jewel of the Crown. When the Blaze Star erupts, it’ll be approximately as bright as Alphecca. The Northern Crown will have 2 jewels! Thank you, Paul!

Why hasn’t it happened yet?

Predicting eruptions of stars is not an exact science. The Blaze Star (T Coronae Borealis) underwent two known eruptions recorded by astronomers. Those events were on May 12, 1866, and on February 9, 1946. Those eruptions were 80 years apart. So scientists thought that, in another 80 years, the star would erupt again. So, 80 years from 1946 would be 2026. Which raises the question: Why did astronomers think the eruption would happen in 2024?

Well, the star brightened and dimmed before its last eruption in 1946. And it has been brightening and dimming now as well, leading some to think the nova would happen sooner rather than later. But it appears as if later is more likely. And so we wait …

In the meantime, here’s how to find Corona Borealis and be ready to see it when the nova arrives.

Why will it go nova?

The Blaze Star isn’t one star but two. It’s a binary system with a white dwarf and a red giant. White dwarfs are stellar remnants, the exposed core of a sunlike star that shed its outer layers at the end of its main-sequence life. It’s a super-dense star with the mass of our sun but only the size of Earth.

Blaze Star’s white dwarf has built up material on its surface, siphoned off from the red giant star. Periodically, it “can’t take no more” and explodes, about every 80 years.

This is our best opportunity to see a nova with some warning. Plus we have great visual context from the surrounding C-shape of stars. So cross your fingers for good weather when it happens.

Artist’s concept of a red giant star and white dwarf star. A stream of material flows from the red giant to the white dwarf, eventually causing a runaway thermonuclear reaction on the white dwarf that will appear as a new star, or nova, in earthly skies. The constellation Corona Borealis the Northern Crown should have a nova appear from the Blaze Star approximately every 80 years. Image via NASA/ Goddard Space Flight Center.

Where to look to find the Blaze Star

The constellation Corona Borealis is back from a month hiding below the horizon. It rotates around Polaris just outside of what we traditionally think of as the circumpolar constellations. This mean it’s not visible all year round for much of the Northern Hemisphere.

The easy-to-find constellation looks distinctly like a backward C at this time of year. It lies between the bright star Arcturus and the squarish four-star shape of Hercules. Look east at the stars coming over the horizon before dawn. Find the bright orange star Arcturus. Then, to the bottom left of Arcturus is the backward C shape of Corona Borealis … unless there’s a guest star messing up the shape!

By the summer these constellations will be high in the sky again. You always need to spend some time dark-adapting your eyes before you see the constellations properly. Plus, binoculars would be a good idea. And you need to be ready to go when we get the news, as it will only be there for a couple of days.

Want to see the Blaze Star go nova? X marks the spot! Astronomers said an impending nova will give the constellation of the Northern Crown – Corona Borealis – an additional star that rivals its brightest star. Image via Chris Harvey/ Stellarium. Used with permission.

How bright will the Blaze Star be?

The actual explosion of the Blaze Star nova will likely dwarf any explosion you’ll ever see. But the star is far away. How bright will it get in our sky? Astronomers expect it to reach an apparent magnitude of 2. That’s a respectable brightness for a star. It’s conveniently comparable to the brightest star in the Northern Crown, the Jewel of the Crown, Alphecca. So, for a few days, the Northern Crown will have two jewels!

T Corana Borealis – the Blaze Star – also one of the most distant stars you’ll ever see. Alphecca is around 75 light-years away, while the Blaze Star is closer to 3,000 light-years away. So that gives you some perspective on the absolute magnitude (brightness) of this enormous blast. And since the light of this explosion has travelled for 3,000 years to get here, in relative terms the nova happened during the Bronze Age.

Remember that, when they are side-by-side with approximately the same brightness, the nova is 40 times farther away than Alphecca. Also, we are not seeing the two stars at the same moment in time. One we see as it was 75 years ago and the other we see as it was 3,000 years ago. It can be hard to get your head around that!

The nova will brighten the star by thousands of times, typically over just a few hours, and then take some days to fade away again. When it’s done, it will go back to its normal appearance.

Late at night in the spring, and high overhead during summer months, find the bright stars Vega and Arcturus. Then locate the constellations Hercules and Boötes. The semicircle of stars between them is the constellation Corona Borealis. Image via NASA.

Finding Corona Borealis, the Northern Crown

If you are not familiar with the Northern Crown, get out and have a look at it before this nova happens. And then, clouds willing, when it does erupt we can go out and see the C shape is harder to spot. Instead, the dominant feature will be two bright-ish stars, Alphecca (the brightest star in Corona Borealis), and the Blaze Star.

The Blaze Star is normally invisible to the unaided eye. On a regular day, it sits at around magnitude 10, making it only the 19th brightest star in the constellation. But as it undergoes a colossal outburst of energy, it will brighten.

Bottom line: We’re still waiting for the Blaze Star to go nova! Will it happen March 27? Here’s how to find Corona Borealis so you’re ready when it does happen.

Source: When will the Next T CrB Eruption Occur?

The post Will the Blaze Star explode on March 27, 2025? first appeared on EarthSky.

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The Enhanced Fujita Scale rates the strength of a tornado

The Moore, Oklahoma, EF5 tornado from May 20, 2013. The incredible destruction from this tornado earned it the top ranking on the Enhanced Fujita Scale. Image via Gabriel Garfield/ National Weather Service.

Deciphering the Enhanced Fujita Scale

When tornados break out, people always want to know, how strong were they? But making that assessment is an in-depth process. It requires site surveys by National Weather Service (NWS) meteorologists, who use damage indicators and degrees of damage to estimate tornado strength. Following the assessment, a tornado gets a rating using the Enhanced Fujita Scale, or EF scale. The scale rates tornadoes from 0 to 5, as follows:

EF0: 65-85 mph (29-38 m/s)
EF1: 86-110 mph (39-49 m/s)
EF2: 111-135 mph (50-60 m/s)
EF3: 136-165 mph (61-73.8 m/s)
EF4: 166-200 mph (74-89 m/s)
EF5: 201+ mph (90+ m/s)

EF0 and EF1 tornadoes are considered “weak”, EF2 and EF3s are “strong” and EF4 and EF5 tornadoes are considered “violent”. While EF4 and EF5 tornadoes are the most devastating, they only make up 2% of all tornadoes.

The 2025 EarthSky lunar calendar makes a great gift. Get yours today!

How are wind strengths measured?

Unlike the Saffir-Simpson Scale, which rates the intensity of hurricanes based on observed or measured wind data, the Enhanced Fujita scale estimates a three-second wind gust. They use this to determine the strength of a tornado at different points of damage along the suspected path.

The scale we use now is an update from the original Fujita, or F-scale, which tornado scientist Ted Fujita introduced in 1971. But the original scale had some drawbacks. It focused solely on damage from the tornado. What if the tornado passed over a field where there was no structural damage to assess? And it did not distinguish between a mobile home versus a masonry-constructed building.

So meteorologists and engineers updated the original F-scale to better reflect damage from tornadoes in relation to wind speed based on how structures are designed. It also looks at damage to vegetation. The EF update became operational in 2007.

An aerial view of tornado damage. Photo by Kelly/ Pexels.

The survey process

The National Weather Service spends hours, and sometimes days, surveying the paths of tornadoes. Meteorologists with the NWS follow the path and identify damage indicators (DI) from a list of 28 different indicators, which include things like damage to barns and outbuildings, schools and trees.

Here are the 28 damage indicators that NWS meteorologists use in their tornado surveys. Chart via NWS.

Within each of the 28 damage indicators, there is also a degree of damage (DOD). For example, the damage indicator for a one- or two-family home has ten degrees of damage ranging from “visible damage” to “destruction of engineered and/or well constructed residence; slab swept clean.”

Within those degrees of damage there are also bounds: expected, lower bounds and upper bounds. Meteorologists evaluate multiple damage indicators along the path of the tornado before they use all the data collected to determine the final EF rating. And they repeat this process for every sustained tornado damage path. (If you want to look at the DOD breakdown of each 28 DI, visit this NWS page and click on the correlating number to each DI.)

An explanation of the degree of damage for a 1- and 2-family residence damage indicator. Chart via NOAA/ Storm Prediction Center.

The history of the Enhanced Fujita Scale

Dr. Tetsuya Theodore (Ted) Fujita of the University of Chicago developed a scale to categorize a tornado’s intensity in February of 1971. This was the Fujita scale, or F-scale. Like the Enhanced Fujita scale we use now, the original Fujita scale also categorized tornadoes from F0-F5.

Fujita hoped his scale would help categorize tornadoes by their intensity. But he also wanted to estimate the wind speed of the tornado by assessing the damage. Just three years later, Fujita and his team would survey every tornado from the Super Outbreak of April 1974. This event solidified the Fujita Scale as the pillar of tornado ranking, until its reevaluation decades later.

While the Fujita scale was groundbreaking, by the late 1990s, meteorologists started to realize that the original wind speed estimates were too high. With the F-scale, an F3 tornado could have wind speeds of 200 miles per hour (90 m/s). But in the current Enhanced Fujita Scale, wind speeds of 200 miles per hour (90 m/s) indicate an EF5.

Meteorologists also determined that the evaluated damage with the F-scale could be too subjective, disregarding construction material. Fujita supported the reevaluation of his original F-scale. However, he died in 1998 and therefore was not alive to see the new scale put into practice in February 2007. It kept the original concept of the F-scale in mind, with modifications to include more damage indicator points.

The most recent EF5 tornado

It’s been more than 10 years since an EF5 tornado hit in the United States. On May 20, 2013, an EF5 tore through Moore, Oklahoma, and surrounding communities. The National Weather Service surveyed the damage and found most of it earned an EF4 rating. But there were a few areas, including at a local elementary school, that were consistent with EF5 damage. The tornado was on the ground for 40 minutes and 14 miles (23 km). At its largest it was 1.1 miles wide (1.8 km). Sadly, 24 people were killed in this tornado, and more than 200 were injured.

Bottom line: National Weather Service meteorologists use the Enhanced Fujita Scale to rate a tornado’s strength. It’s a long process! It requires National Weather Service meteorologists to go out and survey damaged areas, seeking multiple damage indicators and determining the degree of damage of those indicators. They then determine the tornado rating based on these data.

Via NOAA Storm Prediction Center

Read more: Where have the EF5s gone? A closer look at the “drought” of the most violent tornadoes in the United States

Read more: Tornado Alley is shifting toward Dixie

The post The Enhanced Fujita Scale rates the strength of a tornado first appeared on EarthSky.

from EarthSky https://ift.tt/eZA2dQX

The Moore, Oklahoma, EF5 tornado from May 20, 2013. The incredible destruction from this tornado earned it the top ranking on the Enhanced Fujita Scale. Image via Gabriel Garfield/ National Weather Service.

Deciphering the Enhanced Fujita Scale

When tornados break out, people always want to know, how strong were they? But making that assessment is an in-depth process. It requires site surveys by National Weather Service (NWS) meteorologists, who use damage indicators and degrees of damage to estimate tornado strength. Following the assessment, a tornado gets a rating using the Enhanced Fujita Scale, or EF scale. The scale rates tornadoes from 0 to 5, as follows:

EF0: 65-85 mph (29-38 m/s)
EF1: 86-110 mph (39-49 m/s)
EF2: 111-135 mph (50-60 m/s)
EF3: 136-165 mph (61-73.8 m/s)
EF4: 166-200 mph (74-89 m/s)
EF5: 201+ mph (90+ m/s)

EF0 and EF1 tornadoes are considered “weak”, EF2 and EF3s are “strong” and EF4 and EF5 tornadoes are considered “violent”. While EF4 and EF5 tornadoes are the most devastating, they only make up 2% of all tornadoes.

The 2025 EarthSky lunar calendar makes a great gift. Get yours today!

How are wind strengths measured?

Unlike the Saffir-Simpson Scale, which rates the intensity of hurricanes based on observed or measured wind data, the Enhanced Fujita scale estimates a three-second wind gust. They use this to determine the strength of a tornado at different points of damage along the suspected path.

The scale we use now is an update from the original Fujita, or F-scale, which tornado scientist Ted Fujita introduced in 1971. But the original scale had some drawbacks. It focused solely on damage from the tornado. What if the tornado passed over a field where there was no structural damage to assess? And it did not distinguish between a mobile home versus a masonry-constructed building.

So meteorologists and engineers updated the original F-scale to better reflect damage from tornadoes in relation to wind speed based on how structures are designed. It also looks at damage to vegetation. The EF update became operational in 2007.

An aerial view of tornado damage. Photo by Kelly/ Pexels.

The survey process

The National Weather Service spends hours, and sometimes days, surveying the paths of tornadoes. Meteorologists with the NWS follow the path and identify damage indicators (DI) from a list of 28 different indicators, which include things like damage to barns and outbuildings, schools and trees.

Here are the 28 damage indicators that NWS meteorologists use in their tornado surveys. Chart via NWS.

Within each of the 28 damage indicators, there is also a degree of damage (DOD). For example, the damage indicator for a one- or two-family home has ten degrees of damage ranging from “visible damage” to “destruction of engineered and/or well constructed residence; slab swept clean.”

Within those degrees of damage there are also bounds: expected, lower bounds and upper bounds. Meteorologists evaluate multiple damage indicators along the path of the tornado before they use all the data collected to determine the final EF rating. And they repeat this process for every sustained tornado damage path. (If you want to look at the DOD breakdown of each 28 DI, visit this NWS page and click on the correlating number to each DI.)

An explanation of the degree of damage for a 1- and 2-family residence damage indicator. Chart via NOAA/ Storm Prediction Center.

The history of the Enhanced Fujita Scale

Dr. Tetsuya Theodore (Ted) Fujita of the University of Chicago developed a scale to categorize a tornado’s intensity in February of 1971. This was the Fujita scale, or F-scale. Like the Enhanced Fujita scale we use now, the original Fujita scale also categorized tornadoes from F0-F5.

Fujita hoped his scale would help categorize tornadoes by their intensity. But he also wanted to estimate the wind speed of the tornado by assessing the damage. Just three years later, Fujita and his team would survey every tornado from the Super Outbreak of April 1974. This event solidified the Fujita Scale as the pillar of tornado ranking, until its reevaluation decades later.

While the Fujita scale was groundbreaking, by the late 1990s, meteorologists started to realize that the original wind speed estimates were too high. With the F-scale, an F3 tornado could have wind speeds of 200 miles per hour (90 m/s). But in the current Enhanced Fujita Scale, wind speeds of 200 miles per hour (90 m/s) indicate an EF5.

Meteorologists also determined that the evaluated damage with the F-scale could be too subjective, disregarding construction material. Fujita supported the reevaluation of his original F-scale. However, he died in 1998 and therefore was not alive to see the new scale put into practice in February 2007. It kept the original concept of the F-scale in mind, with modifications to include more damage indicator points.

The most recent EF5 tornado

It’s been more than 10 years since an EF5 tornado hit in the United States. On May 20, 2013, an EF5 tore through Moore, Oklahoma, and surrounding communities. The National Weather Service surveyed the damage and found most of it earned an EF4 rating. But there were a few areas, including at a local elementary school, that were consistent with EF5 damage. The tornado was on the ground for 40 minutes and 14 miles (23 km). At its largest it was 1.1 miles wide (1.8 km). Sadly, 24 people were killed in this tornado, and more than 200 were injured.

Bottom line: National Weather Service meteorologists use the Enhanced Fujita Scale to rate a tornado’s strength. It’s a long process! It requires National Weather Service meteorologists to go out and survey damaged areas, seeking multiple damage indicators and determining the degree of damage of those indicators. They then determine the tornado rating based on these data.

Via NOAA Storm Prediction Center

Read more: Where have the EF5s gone? A closer look at the “drought” of the most violent tornadoes in the United States

Read more: Tornado Alley is shifting toward Dixie

The post The Enhanced Fujita Scale rates the strength of a tornado first appeared on EarthSky.

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Is Sirius the most luminous star in the sky?

View larger. | The 3 stars that form the Belt of Orion point toward Sirius, the sky’s brightest star. Image via Tom and Jane Wildoner at Dark Side Observatory. Used with permission.

Maybe you know that Sirius is the brightest star in the night sky. But is Sirius the most luminous star? The answer is no. To astronomers, the word luminous refers to a star’s intrinsic brightness, or its absolute magnitude. To put it more simply, if all the stars were equally distant from Earth, would Sirius be the brightest? Not even close. It just looks bright because it’s close to us, only 8.6 light-years away.

Consider the 25 brightest stars (not counting the sun) as seen from Earth. Sirius is the brightest in apparent magnitude, that is, its brightness as observed from Earth. If you took those exact same 25 stars and ranked them by absolute magnitude, or imagined they were all the same distance from Earth, Sirius would drop from 1st to 21st brightest.

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The brightest star from Earth

Sirius, in the constellation Canis Major the Greater Dog, looks extraordinarily bright in Earth’s sky. It’s our sky’s brightest star (not counting our daytime star, the sun). But its brightness stems primarily from the fact that it’s close to us, only 8.6 light-years away.

No matter where you live on Earth, just follow the three medium-bright stars in Orion’s Belt to locate Sirius.

Sirius is not only the brightest star in the constellation Canis Major the Greater Dog, it’s the brightest star in the sky. You can be sure you’re looking at the correct bright star by drawing a line from Orion’s Belt to Sirius.

The colors of Sirius

Many people comment that they see Sirius flashing colors. This happens when you see Sirius low in the sky. The colors are just the ordinary rainbow colors in white starlight; all starlight is composed of this mixture of colors. We notice the sparkling colors of Sirius more readily, though, because Sirius is so much brighter than most stars.

The extra thickness of the Earth’s atmosphere near the horizon acts like a lens or prism, breaking up starlight into the colors of the rainbow and causing a star to sparkle. When you see Sirius low in the sky, you’re looking through more atmosphere than when the star is overhead.

If you watch, you’ll notice Sirius sparkling less, and appearing less colorful (more strictly white) when it appears higher in the sky.

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!

Stars more luminous than Sirius

Scientists think at least three stars in the constellation Canis Major, where Sirius resides, are thousands of times more luminous than Sirius: Aludra, Wezen and Omicron 2. Although the distances to these faraway stars are not known with precision. Aludra is estimated to lie about 3,200 light-years away. Omicron 2 lies at an estimated 3,600 light-years distant. Wezen is about 1,800 light-years. That’s in contrast to Sirius’ distance of only 8.6 light-years.

When scientists compare stars by absolute magnitude, they imagine that all the stars are 32.6 light-years away. At this distance, our sun would barely be visible as a speck of light. In stark contrast, Aludra, Wezen and Omicron 2 would outshine Sirius by some 100 to 200 times. And Sirius would be about the same brightness as the star Castor in Gemini. Imagine how much different Canis Major would look!

Read more about stellar luminosity, the true brightnesses of stars

View at EarthSky Community Photos. | Daniel Friedman captured this shot from Montauk, New York, on a December evening. Note bright Sirius is on the left, and Orion’s Belt pointing to it. Thank you, Daniel!

Bottom line: Sirius is the brightest star in Earth’s sky because of how close it is to us. It’s so spectacularly bright that you might see glints of different colors flashing from it.

The post Is Sirius the most luminous star in the sky? first appeared on EarthSky.

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View larger. | The 3 stars that form the Belt of Orion point toward Sirius, the sky’s brightest star. Image via Tom and Jane Wildoner at Dark Side Observatory. Used with permission.

Maybe you know that Sirius is the brightest star in the night sky. But is Sirius the most luminous star? The answer is no. To astronomers, the word luminous refers to a star’s intrinsic brightness, or its absolute magnitude. To put it more simply, if all the stars were equally distant from Earth, would Sirius be the brightest? Not even close. It just looks bright because it’s close to us, only 8.6 light-years away.

Consider the 25 brightest stars (not counting the sun) as seen from Earth. Sirius is the brightest in apparent magnitude, that is, its brightness as observed from Earth. If you took those exact same 25 stars and ranked them by absolute magnitude, or imagined they were all the same distance from Earth, Sirius would drop from 1st to 21st brightest.

The 2025 EarthSky lunar calendar makes a great gift. Get yours today!

The brightest star from Earth

Sirius, in the constellation Canis Major the Greater Dog, looks extraordinarily bright in Earth’s sky. It’s our sky’s brightest star (not counting our daytime star, the sun). But its brightness stems primarily from the fact that it’s close to us, only 8.6 light-years away.

No matter where you live on Earth, just follow the three medium-bright stars in Orion’s Belt to locate Sirius.

Sirius is not only the brightest star in the constellation Canis Major the Greater Dog, it’s the brightest star in the sky. You can be sure you’re looking at the correct bright star by drawing a line from Orion’s Belt to Sirius.

The colors of Sirius

Many people comment that they see Sirius flashing colors. This happens when you see Sirius low in the sky. The colors are just the ordinary rainbow colors in white starlight; all starlight is composed of this mixture of colors. We notice the sparkling colors of Sirius more readily, though, because Sirius is so much brighter than most stars.

The extra thickness of the Earth’s atmosphere near the horizon acts like a lens or prism, breaking up starlight into the colors of the rainbow and causing a star to sparkle. When you see Sirius low in the sky, you’re looking through more atmosphere than when the star is overhead.

If you watch, you’ll notice Sirius sparkling less, and appearing less colorful (more strictly white) when it appears higher in the sky.

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!

Stars more luminous than Sirius

Scientists think at least three stars in the constellation Canis Major, where Sirius resides, are thousands of times more luminous than Sirius: Aludra, Wezen and Omicron 2. Although the distances to these faraway stars are not known with precision. Aludra is estimated to lie about 3,200 light-years away. Omicron 2 lies at an estimated 3,600 light-years distant. Wezen is about 1,800 light-years. That’s in contrast to Sirius’ distance of only 8.6 light-years.

When scientists compare stars by absolute magnitude, they imagine that all the stars are 32.6 light-years away. At this distance, our sun would barely be visible as a speck of light. In stark contrast, Aludra, Wezen and Omicron 2 would outshine Sirius by some 100 to 200 times. And Sirius would be about the same brightness as the star Castor in Gemini. Imagine how much different Canis Major would look!

Read more about stellar luminosity, the true brightnesses of stars

View at EarthSky Community Photos. | Daniel Friedman captured this shot from Montauk, New York, on a December evening. Note bright Sirius is on the left, and Orion’s Belt pointing to it. Thank you, Daniel!

Bottom line: Sirius is the brightest star in Earth’s sky because of how close it is to us. It’s so spectacularly bright that you might see glints of different colors flashing from it.

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Most distant known galaxy is mature in a baby universe

EarthSky’s Will Triggs explains what’s so surprising about the discovery of oxygen in the most distant known galaxy.

Most distant known galaxy is mature in a baby universe

In 2024, the James Webb Space Telescope spotted the most distant galaxy we’ve yet seen. It’s named JADES-GS-z14-0, and we’re seeing it back in the Cosmic Dawn, when the universe was just 2% of its current age. And on March 20, 2025, two teams of astronomers said they’ve detected oxygen in this galaxy. This was a surprise, because – based on our current understanding of how the universe developed – stars shouldn’t have been evolved enough to produce heavy elements like oxygen that early in the universe.

One team published their peer-reviewed results in the journal Astronomy & Astrophysics on March 20, 2025. And the other team published their peer-reviewed results on the same day in The Astrophysical Journal.

View larger. | This is the most distant known galaxy, JADES-GS-z14-0. It’s a tiny dot in the Fornax constellation. We are seeing it when the universe was only 300 million years old, or 2% of its current age. The large view is from the James Webb Space Telescope, and the inset is from the Atacama Large Millimeter/submillimeter Array (ALMA). Two research teams recently said they’ve discovered a surprise in this galaxy: oxygen. So the galaxy evolved much quicker in the infant universe than astronomers thought was possible. Image via ALMA (ESO/NAOJ/NRAO)/ S. Carniani et al./ S. Schouws et al/ JWST: NASA/ ESA/ CSA/ STScI/ Brant Robertson (UC Santa Cruz)/ Ben Johnson (CfA)/ Sandro Tacchella (Cambridge)/ Phill Cargile (CfA).

Early universe, older stars

We see JADES-GS-z14-0 as it was 13.4 billion years ago, because that’s how long its light takes to reach us. The universe itself was just around 300 million years old at that time, or about 2% of its current age. This is a time period we call the Cosmic Dawn.

But the astronomers were surprised to find oxygen in this galaxy. Heavier elements, like oxygen, spread throughout a galaxy after the star dies and blows itself apart. So for stars to have spread oxygen in the galaxy, there must have already been a generation of them that lived and died. Young stars are made mostly of hydrogen and helium, so that’s what we’d expect to find in a galaxy at this time. Instead, the new studies show that JADES-GS-z14-0 has around 10 times more heavy elements than they thought possible. Therefore, astronomers have to rethink their ideas of how stars and galaxies lived and died in the early universe.

Lead author of the paper in the The Astrophysical Journal, Sander Schouws of Leiden Observatory in the Netherlands, said:

It is like finding an adolescent where you would only expect babies. The results show the galaxy has formed very rapidly and is also maturing rapidly, adding to a growing body of evidence that the formation of galaxies happens much faster than we expected.

The two new studies found a spike of oxygen in the spectra of the most distant known galaxy, JADES-GS-z14-0. Image via ALMA (ESO/NAOJ/NRAO)/ S. Carniani et al./ S. Schouws et al/ JWST: NASA/ ESA/ CSA/ STScI/ Brant Robertson (UC Santa Cruz)/ Ben Johnson (CfA)/ Sandro Tacchella (Cambridge)/ Phill Cargile (CfA).

A surprise finding

Lead author of the paper in the journal Astronomy & Astrophysics, Stefano Carniani of the Scuola Normale Superiore of Pisa, Italy, said:

I was astonished by the unexpected results because they opened a new view on the first phases of galaxy evolution. The evidence that a galaxy is already mature in the infant universe raises questions about when and how galaxies formed.

In addition, the detection of oxygen allows astronomers to make precise distance measurements for the galaxy. Co-author of the paper in Astronomy & Astrophysics, Eleonora Parlanti of the Scuola Normale Superiore of Pisa, said:

The ALMA detection offers an extraordinarily precise measurement of the galaxy’s distance down to an uncertainty of just 0.005%. This level of precision — analogous to being accurate within 5 cm over a distance of 1 km — helps refine our understanding of distant galaxy properties.

This artist’s concept shows what the most distant known galaxy, JADES-GS-z14-0, might look like. Early galaxies were clumpy and irregular. Image via ESO/ M. Kornmesser.

Bottom line: Astronomers have discovered oxygen in the most distant known galaxy. The finding was a surprise, because it means the stars within are older than we would expect in the early universe.

Source: The eventful life of a luminous galaxy at z = 14: metal enrichment, feedback, and low gas fraction?

Source: Detection of [OIII]88µm in JADES-GS-z14-0 at z=14.1793

Via ESO

The post Most distant known galaxy is mature in a baby universe first appeared on EarthSky.

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EarthSky’s Will Triggs explains what’s so surprising about the discovery of oxygen in the most distant known galaxy.

Most distant known galaxy is mature in a baby universe

In 2024, the James Webb Space Telescope spotted the most distant galaxy we’ve yet seen. It’s named JADES-GS-z14-0, and we’re seeing it back in the Cosmic Dawn, when the universe was just 2% of its current age. And on March 20, 2025, two teams of astronomers said they’ve detected oxygen in this galaxy. This was a surprise, because – based on our current understanding of how the universe developed – stars shouldn’t have been evolved enough to produce heavy elements like oxygen that early in the universe.

One team published their peer-reviewed results in the journal Astronomy & Astrophysics on March 20, 2025. And the other team published their peer-reviewed results on the same day in The Astrophysical Journal.

View larger. | This is the most distant known galaxy, JADES-GS-z14-0. It’s a tiny dot in the Fornax constellation. We are seeing it when the universe was only 300 million years old, or 2% of its current age. The large view is from the James Webb Space Telescope, and the inset is from the Atacama Large Millimeter/submillimeter Array (ALMA). Two research teams recently said they’ve discovered a surprise in this galaxy: oxygen. So the galaxy evolved much quicker in the infant universe than astronomers thought was possible. Image via ALMA (ESO/NAOJ/NRAO)/ S. Carniani et al./ S. Schouws et al/ JWST: NASA/ ESA/ CSA/ STScI/ Brant Robertson (UC Santa Cruz)/ Ben Johnson (CfA)/ Sandro Tacchella (Cambridge)/ Phill Cargile (CfA).

Early universe, older stars

We see JADES-GS-z14-0 as it was 13.4 billion years ago, because that’s how long its light takes to reach us. The universe itself was just around 300 million years old at that time, or about 2% of its current age. This is a time period we call the Cosmic Dawn.

But the astronomers were surprised to find oxygen in this galaxy. Heavier elements, like oxygen, spread throughout a galaxy after the star dies and blows itself apart. So for stars to have spread oxygen in the galaxy, there must have already been a generation of them that lived and died. Young stars are made mostly of hydrogen and helium, so that’s what we’d expect to find in a galaxy at this time. Instead, the new studies show that JADES-GS-z14-0 has around 10 times more heavy elements than they thought possible. Therefore, astronomers have to rethink their ideas of how stars and galaxies lived and died in the early universe.

Lead author of the paper in the The Astrophysical Journal, Sander Schouws of Leiden Observatory in the Netherlands, said:

It is like finding an adolescent where you would only expect babies. The results show the galaxy has formed very rapidly and is also maturing rapidly, adding to a growing body of evidence that the formation of galaxies happens much faster than we expected.

The two new studies found a spike of oxygen in the spectra of the most distant known galaxy, JADES-GS-z14-0. Image via ALMA (ESO/NAOJ/NRAO)/ S. Carniani et al./ S. Schouws et al/ JWST: NASA/ ESA/ CSA/ STScI/ Brant Robertson (UC Santa Cruz)/ Ben Johnson (CfA)/ Sandro Tacchella (Cambridge)/ Phill Cargile (CfA).

A surprise finding

Lead author of the paper in the journal Astronomy & Astrophysics, Stefano Carniani of the Scuola Normale Superiore of Pisa, Italy, said:

I was astonished by the unexpected results because they opened a new view on the first phases of galaxy evolution. The evidence that a galaxy is already mature in the infant universe raises questions about when and how galaxies formed.

In addition, the detection of oxygen allows astronomers to make precise distance measurements for the galaxy. Co-author of the paper in Astronomy & Astrophysics, Eleonora Parlanti of the Scuola Normale Superiore of Pisa, said:

The ALMA detection offers an extraordinarily precise measurement of the galaxy’s distance down to an uncertainty of just 0.005%. This level of precision — analogous to being accurate within 5 cm over a distance of 1 km — helps refine our understanding of distant galaxy properties.

This artist’s concept shows what the most distant known galaxy, JADES-GS-z14-0, might look like. Early galaxies were clumpy and irregular. Image via ESO/ M. Kornmesser.

Bottom line: Astronomers have discovered oxygen in the most distant known galaxy. The finding was a surprise, because it means the stars within are older than we would expect in the early universe.

Source: The eventful life of a luminous galaxy at z = 14: metal enrichment, feedback, and low gas fraction?

Source: Detection of [OIII]88µm in JADES-GS-z14-0 at z=14.1793

Via ESO

The post Most distant known galaxy is mature in a baby universe first appeared on EarthSky.

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March equinox 2025: Here’s all you need to know

The March equinox has arrived! Here’s all you need to know about it.

What is it? The March equinox – aka the vernal equinox – marks the sun’s crossing above Earth’s equator, moving from south to north. Earth’s tilt on its axis is what causes this northward shift of the sun’s path across our sky at this time of year. Earth’s tilt is now bringing spring and summer to the Northern Hemisphere. At the same time, the March equinox marks the beginning of autumn – and a shift toward winter – in the Southern Hemisphere.
When is it? The sun crosses the celestial equator – a line directly above Earth’s equator – at 9:01 UTC on March 20, 2025 (4:01 a.m. CDT).

No matter where you are on Earth, the equinox brings us a number of seasonal effects, noticeable to nature lovers around the globe.

2025 EarthSky lunar calendar is available now. A unique and beautiful poster-sized calendar with phases of the moon for every night of the year. Get yours today!

Equal day and night on the equinox?

At the equinox, Earth’s two hemispheres are receiving the sun’s rays equally. Night and day are often said to be equal in length. In fact, the word equinox comes from the Latin aequus (equal) and nox (night). For our ancestors, whose timekeeping was less precise than ours, day and night likely did seem equal. But today we know it’s not exactly so.

Read more: Are day and night equal at the equinox?

Satellite views of Earth on the solstices and equinoxes. We are at the March equinox now. Read more about this image. Images via NASA Earth Observatory.

Fastest sunsets at the equinoxes

The fastest sunsets and sunrises of the year happen at the equinoxes. We’re talking here about the length of time it takes for the whole sun to sink below the horizon.

Read more: Fastest sunsets happen near equinoxes

View at EarthSky Community Photos. | Iaroslav Kourzenkov of Halifax, Nova Scotia, Canada, captured this image of the sunset on the equinox on March 20, 2023. Thank you, Iaroslav!

Sun rises due east and sets due west?

Here’s another equinox phenomenon. You might hear that the sun rises due east and sets due west at the equinox. Is that true? Yes it is. In fact, it’s the case no matter where you live on Earth, with the exception of the North and South Poles. At the equinoxes, the sun appears overhead at noon as seen from Earth’s equator, as the illustration below shows. This illustration shows the sun’s location on the celestial equator, every hour, on the day of the equinox.

No matter where you are on Earth – except at the Earth’s North and South Poles – you have a due east and due west point on your horizon. That point marks the intersection of your horizon with the celestial equator: the imaginary line above the true equator of the Earth.

The sun is on the celestial equator, and the celestial equator intersects all of our horizons at points due east and due west. Voila! The sun rises due east and sets due west.

Read more: Sun rises due east and sets due west

The day arc of the sun, every hour, at the equinox, as seen on the (imaginary) celestial sphere surrounding Earth. At the equinox, the sun is directly above Earth’s equator. Image via Tau’olunga/ Wikimedia Commons (CC BY-SA 2.5).

More March equinox effects

And there are also plenty more effects in play around the time of the March equinox that all of us can notice. In the Northern Hemisphere, the March equinox brings earlier sunrises, later sunsets and sprouting plants.

Meanwhile, you’ll find the opposite season – later sunrises, earlier sunsets, chillier winds, dry and falling leaves – south of the equator.

The equinoxes and solstices are caused by Earth’s tilt on its axis and ceaseless motion in orbit. You can think of an equinox as happening on the imaginary dome of our sky, or as an event that happens in Earth’s orbit around the sun.

The Earth-centered view

If you think of it from an Earth-centered perspective, you can think of the celestial equator as a great circle dividing Earth’s sky into its Northern and Southern Hemispheres. The celestial equator is an imaginary line wrapping the sky directly above Earth’s equator. At the equinox, the sun crosses the celestial equator to enter the sky’s Northern Hemisphere.

The day arc of the equinox sun as seen from Earth’s equator. Also showing are twilight suns (in red) down to -18 degrees altitude. Note that the sun is at its highest point at noon. And see that the tree’s shadow at noon is cast straight down. That is – as seen from the equator on the day of an equinox – a tree stands in the center of its own shadow. Image via Tau’olunga/ Wikimedia Commons (CC BY-SA 2.5).

The Earth-in-space view

If you think of it from an Earth-in-space perspective, you have to think of Earth in orbit around the sun. And we all know Earth doesn’t orbit upright but is instead tilted on its axis by 23 1/2 degrees. So Earth’s Northern and Southern Hemispheres trade places in receiving the sun’s light and warmth most directly. We have an equinox twice a year – spring and fall – when the tilt of the Earth’s axis and Earth’s orbit around the sun combine in such a way that the axis is inclined neither away from nor toward the sun.

Here are satellite views of Earth on the solstices and equinoxes, via NASA Earth Observatory.

Things change fast around the equinoxes

Since Earth never stops moving around the sun, the position of the sunrise and sunset – and the days of approximately equal sunlight and night – will change quickly.

The video below was the Astronomy Picture of the Day for March 19, 2014. APOD explained:

At an equinox, the Earth’s terminator – the dividing line between day and night – becomes vertical and connects the North and South Poles. The time-lapse video [above] demonstrates this by displaying an entire year on planet Earth in 12 seconds. From geosynchronous orbit, the Meteosat satellite recorded these infrared images of the Earth every day at the same local time. The video started at the September 2010 equinox with the terminator line being vertical.

As the Earth revolved around the sun, the terminator was seen to tilt in a way that provides less daily sunlight to the Northern Hemisphere, causing winter in the north. As the year progressed, the March 2011 equinox arrived halfway through the video, followed by the terminator tilting the other way, causing winter in the Southern Hemisphere and summer in the north. The captured year ends again with the September equinox, concluding another of billions of trips the Earth has taken – and will take – around the sun.

The equinox is an event that takes place in Earth’s orbit around the sun. Image via National Weather Service/ weather.gov.

Where are signs of the March equinox in nature?

Everywhere! Forget about the weather for a moment, and think only about daylight. In terms of daylight, the knowledge that spring is here – and summer is coming – permeates all of nature on the northern half of Earth’s globe.

Notice the arc of the sun across the sky each day. You’ll find that it’s shifting toward the north. Responding to the change in daylight, birds and butterflies are migrating back northward, too, along with the path of the sun.

The longer days do bring with them warmer weather. People are leaving their winter coats at home. Trees are budding, and plants are beginning a new cycle of growth. In many places, spring flowers are beginning to bloom.

Meanwhile, in the Southern Hemisphere, the days are getting shorter and nights longer. A chill is in the air. Fall is here, and winter is coming!

Bottom line: Happy equinox! The 2025 March equinox falls March 20 at 9:01 UTC. So many parts of the world will see the equinox arrive on March 19. All you need to know here.

The post March equinox 2025: Here’s all you need to know first appeared on EarthSky.

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The March equinox has arrived! Here’s all you need to know about it.

What is it? The March equinox – aka the vernal equinox – marks the sun’s crossing above Earth’s equator, moving from south to north. Earth’s tilt on its axis is what causes this northward shift of the sun’s path across our sky at this time of year. Earth’s tilt is now bringing spring and summer to the Northern Hemisphere. At the same time, the March equinox marks the beginning of autumn – and a shift toward winter – in the Southern Hemisphere.
When is it? The sun crosses the celestial equator – a line directly above Earth’s equator – at 9:01 UTC on March 20, 2025 (4:01 a.m. CDT).

No matter where you are on Earth, the equinox brings us a number of seasonal effects, noticeable to nature lovers around the globe.

2025 EarthSky lunar calendar is available now. A unique and beautiful poster-sized calendar with phases of the moon for every night of the year. Get yours today!

Equal day and night on the equinox?

At the equinox, Earth’s two hemispheres are receiving the sun’s rays equally. Night and day are often said to be equal in length. In fact, the word equinox comes from the Latin aequus (equal) and nox (night). For our ancestors, whose timekeeping was less precise than ours, day and night likely did seem equal. But today we know it’s not exactly so.

Read more: Are day and night equal at the equinox?

Satellite views of Earth on the solstices and equinoxes. We are at the March equinox now. Read more about this image. Images via NASA Earth Observatory.

Fastest sunsets at the equinoxes

The fastest sunsets and sunrises of the year happen at the equinoxes. We’re talking here about the length of time it takes for the whole sun to sink below the horizon.

Read more: Fastest sunsets happen near equinoxes

View at EarthSky Community Photos. | Iaroslav Kourzenkov of Halifax, Nova Scotia, Canada, captured this image of the sunset on the equinox on March 20, 2023. Thank you, Iaroslav!

Sun rises due east and sets due west?

Here’s another equinox phenomenon. You might hear that the sun rises due east and sets due west at the equinox. Is that true? Yes it is. In fact, it’s the case no matter where you live on Earth, with the exception of the North and South Poles. At the equinoxes, the sun appears overhead at noon as seen from Earth’s equator, as the illustration below shows. This illustration shows the sun’s location on the celestial equator, every hour, on the day of the equinox.

No matter where you are on Earth – except at the Earth’s North and South Poles – you have a due east and due west point on your horizon. That point marks the intersection of your horizon with the celestial equator: the imaginary line above the true equator of the Earth.

The sun is on the celestial equator, and the celestial equator intersects all of our horizons at points due east and due west. Voila! The sun rises due east and sets due west.

Read more: Sun rises due east and sets due west

The day arc of the sun, every hour, at the equinox, as seen on the (imaginary) celestial sphere surrounding Earth. At the equinox, the sun is directly above Earth’s equator. Image via Tau’olunga/ Wikimedia Commons (CC BY-SA 2.5).

More March equinox effects

And there are also plenty more effects in play around the time of the March equinox that all of us can notice. In the Northern Hemisphere, the March equinox brings earlier sunrises, later sunsets and sprouting plants.

Meanwhile, you’ll find the opposite season – later sunrises, earlier sunsets, chillier winds, dry and falling leaves – south of the equator.

The equinoxes and solstices are caused by Earth’s tilt on its axis and ceaseless motion in orbit. You can think of an equinox as happening on the imaginary dome of our sky, or as an event that happens in Earth’s orbit around the sun.

The Earth-centered view

If you think of it from an Earth-centered perspective, you can think of the celestial equator as a great circle dividing Earth’s sky into its Northern and Southern Hemispheres. The celestial equator is an imaginary line wrapping the sky directly above Earth’s equator. At the equinox, the sun crosses the celestial equator to enter the sky’s Northern Hemisphere.

The day arc of the equinox sun as seen from Earth’s equator. Also showing are twilight suns (in red) down to -18 degrees altitude. Note that the sun is at its highest point at noon. And see that the tree’s shadow at noon is cast straight down. That is – as seen from the equator on the day of an equinox – a tree stands in the center of its own shadow. Image via Tau’olunga/ Wikimedia Commons (CC BY-SA 2.5).

The Earth-in-space view

If you think of it from an Earth-in-space perspective, you have to think of Earth in orbit around the sun. And we all know Earth doesn’t orbit upright but is instead tilted on its axis by 23 1/2 degrees. So Earth’s Northern and Southern Hemispheres trade places in receiving the sun’s light and warmth most directly. We have an equinox twice a year – spring and fall – when the tilt of the Earth’s axis and Earth’s orbit around the sun combine in such a way that the axis is inclined neither away from nor toward the sun.

Here are satellite views of Earth on the solstices and equinoxes, via NASA Earth Observatory.

Things change fast around the equinoxes

Since Earth never stops moving around the sun, the position of the sunrise and sunset – and the days of approximately equal sunlight and night – will change quickly.

The video below was the Astronomy Picture of the Day for March 19, 2014. APOD explained:

At an equinox, the Earth’s terminator – the dividing line between day and night – becomes vertical and connects the North and South Poles. The time-lapse video [above] demonstrates this by displaying an entire year on planet Earth in 12 seconds. From geosynchronous orbit, the Meteosat satellite recorded these infrared images of the Earth every day at the same local time. The video started at the September 2010 equinox with the terminator line being vertical.

As the Earth revolved around the sun, the terminator was seen to tilt in a way that provides less daily sunlight to the Northern Hemisphere, causing winter in the north. As the year progressed, the March 2011 equinox arrived halfway through the video, followed by the terminator tilting the other way, causing winter in the Southern Hemisphere and summer in the north. The captured year ends again with the September equinox, concluding another of billions of trips the Earth has taken – and will take – around the sun.

The equinox is an event that takes place in Earth’s orbit around the sun. Image via National Weather Service/ weather.gov.

Where are signs of the March equinox in nature?

Everywhere! Forget about the weather for a moment, and think only about daylight. In terms of daylight, the knowledge that spring is here – and summer is coming – permeates all of nature on the northern half of Earth’s globe.

Notice the arc of the sun across the sky each day. You’ll find that it’s shifting toward the north. Responding to the change in daylight, birds and butterflies are migrating back northward, too, along with the path of the sun.

The longer days do bring with them warmer weather. People are leaving their winter coats at home. Trees are budding, and plants are beginning a new cycle of growth. In many places, spring flowers are beginning to bloom.

Meanwhile, in the Southern Hemisphere, the days are getting shorter and nights longer. A chill is in the air. Fall is here, and winter is coming!

Bottom line: Happy equinox! The 2025 March equinox falls March 20 at 9:01 UTC. So many parts of the world will see the equinox arrive on March 19. All you need to know here.

The post March equinox 2025: Here’s all you need to know first appeared on EarthSky.

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Are day and night equal on the equinox? Not exactly

Satellite views of Earth on the solstices and equinoxes. We are at the March equinox now. Are day and night equal on the equinox? Read below to find out. Images via NASA Earth Observatory.

More day than night

The March equinox will come on Thursday, March 20, 2025, at 9:01 UTC (4:01 a.m. CDT). It’s the Northern Hemisphere’s spring equinox and Southern Hemisphere’s autumn equinox. You sometimes hear it said that, at the equinoxes, everyone receives about equal daylight and darkness. But there’s really more daylight than darkness at the equinox, eight more minutes or so at mid-temperate latitudes. Two factors explain why we have more than 12 hours of daylight on this day of supposedly equal day and night. They are:

1. The sun is a disk, not a point.

2. Atmospheric refraction.

Read more about the March 2025 equinox: All you need to know

The sun is a disk, not a point

Watch any sunset, and you know the sun appears in Earth’s sky as a disk.

It’s not point-like, as stars are, and yet – by definition – most almanacs regard sunrise as when the leading edge of the sun first touches the eastern horizon. They define sunset as when the sun’s trailing edge finally touches the western horizon.

This provides an extra 2 1/2 to 3 minutes of daylight at mid-temperate latitudes.

Atmospheric refraction raises the sun about 1/2 degree upward in our sky at both sunrise and sunset. This advances the time of actual sunrise, while delaying the time of actual sunset. The result is several minutes of extra daylight, not just at an equinox, but every day. Image via Wikipedia (CC BY-SA 3.0).

2025 EarthSky lunar calendar is available now. A unique and beautiful poster-sized calendar with phases of the moon for every night of the year. Get yours today!

Atmospheric refraction

The Earth’s atmosphere acts like a lens or prism, uplifting the sun about 0.5 degrees from its true geometrical position whenever the sun nears the horizon. Coincidentally, the sun’s angular diameter spans about 0.5 degrees, as well.

In other words, when you see the sun on the horizon, it’s actually just below the horizon geometrically.

What does atmospheric refraction mean for the length of daylight? It advances the sunrise and delays the sunset, adding nearly another six minutes of daylight at mid-temperate latitudes. Hence, more daylight than night at the equinox.

Astronomical almanacs usually don’t give sunrise or sunset times to the second. That’s because atmospheric refraction varies somewhat, depending on air temperature, humidity and barometric pressure. Lower temperature, higher humidity and higher barometric pressure all increase atmospheric refraction.

On the day of the equinox, the center of the sun would set about 12 hours after rising – given a level horizon, as at sea – and no atmospheric refraction.

Are day and night equal?

So, no, day and night are not exactly equal at the equinox.

And here’s a new word for you, equilux. The word is used to describe the day on which day and night are equal. The equilux happens a few to several days after the autumn equinox, and a few to several days before the spring equinox.

Much as earliest sunrises and latest sunsets vary with latitude, so the exact date of an equilux varies with latitude. That’s in contrast to the equinox itself, which is a whole-Earth event, happening at the same instant worldwide. At and near the equator, there is no equilux whatsoever, because the daylight period is over 12 hours long every day of the year.

Visit timeanddate.com for the approximate date of equal day and night at your latitude

Illustrations like this one make it seem as if day and night should be equal at the equinox. In fact, they aren’t exactly equal. Image via Wikimedia Commons (CC BY-SA 3.0).

Bottom line: There’s slightly more day than night on the day of an equinox. That’s because the sun is a disk, not a point of light, and because Earth’s atmosphere refracts (bends) sunlight.

The post Are day and night equal on the equinox? Not exactly first appeared on EarthSky.

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Satellite views of Earth on the solstices and equinoxes. We are at the March equinox now. Are day and night equal on the equinox? Read below to find out. Images via NASA Earth Observatory.

More day than night

The March equinox will come on Thursday, March 20, 2025, at 9:01 UTC (4:01 a.m. CDT). It’s the Northern Hemisphere’s spring equinox and Southern Hemisphere’s autumn equinox. You sometimes hear it said that, at the equinoxes, everyone receives about equal daylight and darkness. But there’s really more daylight than darkness at the equinox, eight more minutes or so at mid-temperate latitudes. Two factors explain why we have more than 12 hours of daylight on this day of supposedly equal day and night. They are:

1. The sun is a disk, not a point.

2. Atmospheric refraction.

Read more about the March 2025 equinox: All you need to know

The sun is a disk, not a point

Watch any sunset, and you know the sun appears in Earth’s sky as a disk.

It’s not point-like, as stars are, and yet – by definition – most almanacs regard sunrise as when the leading edge of the sun first touches the eastern horizon. They define sunset as when the sun’s trailing edge finally touches the western horizon.

This provides an extra 2 1/2 to 3 minutes of daylight at mid-temperate latitudes.

Atmospheric refraction raises the sun about 1/2 degree upward in our sky at both sunrise and sunset. This advances the time of actual sunrise, while delaying the time of actual sunset. The result is several minutes of extra daylight, not just at an equinox, but every day. Image via Wikipedia (CC BY-SA 3.0).

2025 EarthSky lunar calendar is available now. A unique and beautiful poster-sized calendar with phases of the moon for every night of the year. Get yours today!

Atmospheric refraction

The Earth’s atmosphere acts like a lens or prism, uplifting the sun about 0.5 degrees from its true geometrical position whenever the sun nears the horizon. Coincidentally, the sun’s angular diameter spans about 0.5 degrees, as well.

In other words, when you see the sun on the horizon, it’s actually just below the horizon geometrically.

What does atmospheric refraction mean for the length of daylight? It advances the sunrise and delays the sunset, adding nearly another six minutes of daylight at mid-temperate latitudes. Hence, more daylight than night at the equinox.

Astronomical almanacs usually don’t give sunrise or sunset times to the second. That’s because atmospheric refraction varies somewhat, depending on air temperature, humidity and barometric pressure. Lower temperature, higher humidity and higher barometric pressure all increase atmospheric refraction.

On the day of the equinox, the center of the sun would set about 12 hours after rising – given a level horizon, as at sea – and no atmospheric refraction.

Are day and night equal?

So, no, day and night are not exactly equal at the equinox.

And here’s a new word for you, equilux. The word is used to describe the day on which day and night are equal. The equilux happens a few to several days after the autumn equinox, and a few to several days before the spring equinox.

Much as earliest sunrises and latest sunsets vary with latitude, so the exact date of an equilux varies with latitude. That’s in contrast to the equinox itself, which is a whole-Earth event, happening at the same instant worldwide. At and near the equator, there is no equilux whatsoever, because the daylight period is over 12 hours long every day of the year.

Visit timeanddate.com for the approximate date of equal day and night at your latitude

Illustrations like this one make it seem as if day and night should be equal at the equinox. In fact, they aren’t exactly equal. Image via Wikimedia Commons (CC BY-SA 3.0).

Bottom line: There’s slightly more day than night on the day of an equinox. That’s because the sun is a disk, not a point of light, and because Earth’s atmosphere refracts (bends) sunlight.

The post Are day and night equal on the equinox? Not exactly first appeared on EarthSky.

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New evidence: humans and Neanderthals interacted in Israel

Scientist excavating in Tinshemet Cave in central Israel. Findings from this research have provided more evidence that modern humans and Neanderthals in the Levant interacted with each other. Image via Yossi Zaidner / The Hebrew University of Jerusalem.

• Excavations at Tinshemet Cave in Israel provide more evidence that early modern humans and Neanderthals co-existed and interacted.
• Stone tools, animal bones and ochre found at Tinshemet Cave and other archaeological sites in the Levant indicate that the two human species were sharing cultural and technological practices.
• Formal burial customs were another shared practice. Remains of five ancient humans were found at Tinshemet Cave with animal bones and ochre.

More evidence that modern humans and Neanderthals co-existed

Scientists are excavating a site in central Israel called Tinshemet Cave, once occupied by humans during the mid-Middle Paleolithic (130,000 to 80,000 years ago). On March 11, 2025, the researchers said their discoveries, when considered with wider regional archaeological findings, indicate that early modern humans and Neanderthals interacted with each other. As a result, these two human species developed common technological and cultural practices. Furthermore, scientists found five intentional human burials that dated to about 100,000 years ago.

The researchers published their first findings on this archaeological site in the peer-reviewed journal Nature Human Behavior on March 11, 2025.

The Levant, where two human species once met

Scientists have known that early modern humans (Homo sapiens) and Neanderthals (Homo neanderthalensis) once co-existed in the south Levant during the mid-Middle Paleolithic. That’s an area along the eastern Mediterranean that includes modern-day Israel, Jordan and Lebanon.

Modern humans first migrated out of Africa about 300,000 years ago. Around the same time, Neanderthals emerged from Europe. Their migratory paths crossed for the first time in the Levant during the Middle Paleolithic (300,000 to 50,000 years ago). And these two human species left behind archaeological traces of their presence in the region.

For decades, researchers have been studying what these ancient humans left behind. They had questions: What was the relationship between these two human species? Were they competitors for resources or did they cooperate? Was there conflict between them?

What scientists found at Tinshemet Cave

Excavations at Tinshemet Cave, which started in 2017, have yielded a trove of artifacts and several intentional human burials.

Scientists found animal bones of large ungulates (hoofed mammals) that had been hunted for food. And they saw cuts and scrapes on some bones. Also, researchers have found bones from the same animal species in other archaeological sites of the same timeframe. Furthermore, they’ve found animal bones in human burial sites, perhaps as part of a ritual internment.

Researchers also recovered stone tools bearing similar features to those found in other nearby archeological sites. This indicated that modern humans and Neanderthals used the same techniques to create those stone tools. In addition, the scientists discovered evidence of fire use at the cave, such as wood ash.

One of the stone tools found at Tinshemet Cave. These tools, and tools from other sites, indicate that modern humans and Neanderthals used the same techniques to make them. Image via Marion Prévost/ The Hebrew University of Jerusalem.

Furthermore, the researchers found ochre at the cave. Ochre is a yellow to orange-colored clay pigment widely used for cultural purposes, including burial practices, during the mid-Middle Paleolithic. Scientists think that its cultural use indicated the rise of symbolic thought in humans. The Tinshemet Cave inhabitants must have placed great value in it because ochre is not locally available, and they had to travel great distances to obtain it.

Ochre samples from Tinshemet Cave. Scientists found some of it in burial pits, which indicates early people used it for cultural purposes. Image via Yossi Zaidner/ The Hebrew University of Jerusalem.

Evidence of cultural exchange between modern humans and Neanderthals

In their study, the researchers compared what they found at Tinshemet Cave with findings from other Levant archeaological sites of the same timeframe. They studied how early people created stone tools, the kinds of animals they hunted, as well as artifacts that revealed the symbolic behavior and social complexities of these early humans.

Lead author Yossi Zaidner of the Hebrew University of Jerusalem said:

Our data show that human connections and population interactions have been fundamental in driving cultural and technological innovations throughout history.

And the scientists wrote in their paper:

Viewed from the perspective of other key regional sites of this period, our findings indicate consolidation of a uniform behavioral set in the Levantine mid-MP [mid-Middle Paleolithic], consisting of similar lithic technology [stone tools], an increased reliance on large-game hunting and a range of socially elaborated behaviors, comprising intentional human burial and the use of ochre in burial contexts. We suggest that the development of this behavioral uniformity is due to intensified inter-population interactions and admixture between Homo groups ~130–80 ka [thousand years ago].

An artist’s representation of modern humans and Neanderthals sharing cultural, hunting and technological practices. Image via Efrat Bakshitz/ The Hebrew University of Jerusalem.

Human burials at Tinshemet Cave

What scientists describe as “formal burial customs” first appeared about 110,000 years ago in Israel. They think it’s a practice that caught on due to increased social interactions among early modern humans and Neanderthals.

At Tinshemet Cave, they discovered the remains of five humans that were interred about 100,000 years ago. Two of the individuals they recovered were full skeletons, an adult and child, while others were partial skeletons. The bodies had been placed in a sleeping or fetal position, lying on the side with legs bent, arms toward the face and chest, and head bent down.

The scientists also found stone tools, animal bones and pieces of ochre in the burial pits. This suggested a ritual practice and perhaps even a belief system (such as belief in the afterlife). Was Tinshemet Cave a burial ground? It’s too early to know for sure, and excavations are continuing at the site.

Bottom line: A new study of artifacts and human remains from Tinshemet Cave in central Israel provides more evidence that modern humans and Neanderthals in the Levant interacted with each other.

Source: Evidence from Tinshemet Cave in Israel suggests behavioural uniformity across Homo groups in the Levantine mid-Middle Palaeolithic circa 130,000–80,000 years ago

Via American Friends of the Hebrew University

Read more: Did social isolation drive Neanderthals to extinction?

The post New evidence: humans and Neanderthals interacted in Israel first appeared on EarthSky.

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Scientist excavating in Tinshemet Cave in central Israel. Findings from this research have provided more evidence that modern humans and Neanderthals in the Levant interacted with each other. Image via Yossi Zaidner / The Hebrew University of Jerusalem.

• Excavations at Tinshemet Cave in Israel provide more evidence that early modern humans and Neanderthals co-existed and interacted.
• Stone tools, animal bones and ochre found at Tinshemet Cave and other archaeological sites in the Levant indicate that the two human species were sharing cultural and technological practices.
• Formal burial customs were another shared practice. Remains of five ancient humans were found at Tinshemet Cave with animal bones and ochre.

More evidence that modern humans and Neanderthals co-existed

Scientists are excavating a site in central Israel called Tinshemet Cave, once occupied by humans during the mid-Middle Paleolithic (130,000 to 80,000 years ago). On March 11, 2025, the researchers said their discoveries, when considered with wider regional archaeological findings, indicate that early modern humans and Neanderthals interacted with each other. As a result, these two human species developed common technological and cultural practices. Furthermore, scientists found five intentional human burials that dated to about 100,000 years ago.

The researchers published their first findings on this archaeological site in the peer-reviewed journal Nature Human Behavior on March 11, 2025.

The Levant, where two human species once met

Scientists have known that early modern humans (Homo sapiens) and Neanderthals (Homo neanderthalensis) once co-existed in the south Levant during the mid-Middle Paleolithic. That’s an area along the eastern Mediterranean that includes modern-day Israel, Jordan and Lebanon.

Modern humans first migrated out of Africa about 300,000 years ago. Around the same time, Neanderthals emerged from Europe. Their migratory paths crossed for the first time in the Levant during the Middle Paleolithic (300,000 to 50,000 years ago). And these two human species left behind archaeological traces of their presence in the region.

For decades, researchers have been studying what these ancient humans left behind. They had questions: What was the relationship between these two human species? Were they competitors for resources or did they cooperate? Was there conflict between them?

What scientists found at Tinshemet Cave

Excavations at Tinshemet Cave, which started in 2017, have yielded a trove of artifacts and several intentional human burials.

Scientists found animal bones of large ungulates (hoofed mammals) that had been hunted for food. And they saw cuts and scrapes on some bones. Also, researchers have found bones from the same animal species in other archaeological sites of the same timeframe. Furthermore, they’ve found animal bones in human burial sites, perhaps as part of a ritual internment.

Researchers also recovered stone tools bearing similar features to those found in other nearby archeological sites. This indicated that modern humans and Neanderthals used the same techniques to create those stone tools. In addition, the scientists discovered evidence of fire use at the cave, such as wood ash.

One of the stone tools found at Tinshemet Cave. These tools, and tools from other sites, indicate that modern humans and Neanderthals used the same techniques to make them. Image via Marion Prévost/ The Hebrew University of Jerusalem.

Furthermore, the researchers found ochre at the cave. Ochre is a yellow to orange-colored clay pigment widely used for cultural purposes, including burial practices, during the mid-Middle Paleolithic. Scientists think that its cultural use indicated the rise of symbolic thought in humans. The Tinshemet Cave inhabitants must have placed great value in it because ochre is not locally available, and they had to travel great distances to obtain it.

Ochre samples from Tinshemet Cave. Scientists found some of it in burial pits, which indicates early people used it for cultural purposes. Image via Yossi Zaidner/ The Hebrew University of Jerusalem.

Evidence of cultural exchange between modern humans and Neanderthals

In their study, the researchers compared what they found at Tinshemet Cave with findings from other Levant archeaological sites of the same timeframe. They studied how early people created stone tools, the kinds of animals they hunted, as well as artifacts that revealed the symbolic behavior and social complexities of these early humans.

Lead author Yossi Zaidner of the Hebrew University of Jerusalem said:

Our data show that human connections and population interactions have been fundamental in driving cultural and technological innovations throughout history.

And the scientists wrote in their paper:

Viewed from the perspective of other key regional sites of this period, our findings indicate consolidation of a uniform behavioral set in the Levantine mid-MP [mid-Middle Paleolithic], consisting of similar lithic technology [stone tools], an increased reliance on large-game hunting and a range of socially elaborated behaviors, comprising intentional human burial and the use of ochre in burial contexts. We suggest that the development of this behavioral uniformity is due to intensified inter-population interactions and admixture between Homo groups ~130–80 ka [thousand years ago].

An artist’s representation of modern humans and Neanderthals sharing cultural, hunting and technological practices. Image via Efrat Bakshitz/ The Hebrew University of Jerusalem.

Human burials at Tinshemet Cave

What scientists describe as “formal burial customs” first appeared about 110,000 years ago in Israel. They think it’s a practice that caught on due to increased social interactions among early modern humans and Neanderthals.

At Tinshemet Cave, they discovered the remains of five humans that were interred about 100,000 years ago. Two of the individuals they recovered were full skeletons, an adult and child, while others were partial skeletons. The bodies had been placed in a sleeping or fetal position, lying on the side with legs bent, arms toward the face and chest, and head bent down.

The scientists also found stone tools, animal bones and pieces of ochre in the burial pits. This suggested a ritual practice and perhaps even a belief system (such as belief in the afterlife). Was Tinshemet Cave a burial ground? It’s too early to know for sure, and excavations are continuing at the site.

Bottom line: A new study of artifacts and human remains from Tinshemet Cave in central Israel provides more evidence that modern humans and Neanderthals in the Levant interacted with each other.

Source: Evidence from Tinshemet Cave in Israel suggests behavioural uniformity across Homo groups in the Levantine mid-Middle Palaeolithic circa 130,000–80,000 years ago

Via American Friends of the Hebrew University

Read more: Did social isolation drive Neanderthals to extinction?

The post New evidence: humans and Neanderthals interacted in Israel first appeared on EarthSky.

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