Could there be life in helium atmospheres on exoplanets?

View larger. | Artist’s concept of an exoplanet with a helium-dominated atmosphere. A new study suggests that there could be life in helium atmospheres on rocky exoplanets. Image via NASA/ JPL-Caltech.

• Could life exist on exoplanets with helium atmospheres? A new study suggests it’s possible.
• Experiments showed that helium-dominated atmospheres would be non-toxic to many types of earthly lifeforms.
• Helium atmospheres could also preserve other gases associated with life, making them easier to detect by astronomers.

Science news, night sky events and beautiful photos, all in one place. Click here to subscribe to our free daily newsletter.

Life in helium atmospheres on exoplanets?

When searching for possible signs of alien life on exoplanets, scientists tend to focus on atmospheres that might be earthlike. That is, atmospheres dominated by nitrogen, oxygen or even carbon dioxide. But there’s another possibility that has been largely overlooked. What about helium atmospheres?

Helium is the second-most abundant element in the universe. And we know there are exoplanets with helium in their atmospheres.

A new paper just released from researchers at Massachusetts Institute of Technology (MIT) in the U.S. and Wroclaw University of Science and Technology and JJ Scientific in Poland, examines the possibility of life existing in helium atmospheres. Intriguingly, the researchers found that there are no intrinsic barriers that would prevent life as we know it from being able to survive in a helium-dominated atmosphere.

The new study looks at a largely overlooked body of laboratory research on life in helium-dominated atmospheres. And the results are surprising.

The researchers published their preprint version of the paper (not yet peer-reviewed) on August 16, 2026, on arXiv.

An overlooked possibility

Scientists had largely ignored the idea that planets with helium atmospheres could support life. This was based on two key assumptions.

The first was that helium is expected to typically escape from the atmospheres of rocky planets, along with hydrogen. The second is that Earth itself doesn’t have much helium in its atmosphere. So those were the models scientists had to work with.

But the research team decided to take a closer look at the possibility of life on helium worlds. So they synthesized helium-dominated atmospheres in the laboratory. And a wide variety of organisms were subjected to that environment. These included bacteria, fungi, protozoa, microalgae, plants and animals. The results were surprising.

When the organisms had the essential metabolic requirements – the chemical processes in your body that change food into energy and build or repair cells – then they were able to tolerate and survive in the helium atmosphere.

No barriers to life

Overall, the helium did not present any barriers to life. In fact, there was no demonstrated toxicity and no fundamental barrier to metabolism, cell division, photosynthesis, nitrogen fixation or coordinated multicellular activity, including in humans. This suggests that life could survive and even thrive on planets with helium atmospheres.

And it’s seemingly because helium is chemically inert. Whether or not it would actually help life flourish is another question. But it won’t hamper or destroy it.

This is also good news for scientists trying to detect signs of life in helium atmospheres. The helium won’t destroy any biosignature gases present in the atmosphere. And it won’t obscure their spectral signatures. In fact, helium-dominated atmospheres also have low mean molecular weights and large scale heights. This actually strengthens spectral features in transmission and improves remote detectability.

Helium could help scientists find alien life

Not only does this show alien life could exist in a helium atmosphere, it could help scientists actually find it. As the paper concludes:

The possibility of helium-dominated, temperate exoplanet atmospheres asks us to widen a familiar assumption: that life-bearing atmospheres must resemble Earth’s in their bulk composition. Helium contributes little chemistry of its own, yet that very inertness allows the gases required by life to coexist within a stable atmospheric envelope, while its low molecular weight may make their spectral signatures unusually accessible.

The fact that such diverse forms of life can survive, metabolize and reproduce under helium-dominated conditions supports the inclusion of helium-dominated exoplanets among the targets in the search for life beyond Earth.

The convergence of atmospheric-evolution models, the first observations of helium around a habitable-zone rocky planet and decades of laboratory evidence establishes that helium is not an exotic obstacle to life and might in fact enable the first biosignature gas detection on a rocky world in our galaxy.

Last month, researchers reported detecting helium escaping from exoplanet LHS 1140 b. That means it must have an atmosphere, but scientists don’t yet know what other gases are in it. This is an artist’s concept of the planet in question. Image via Melissa Weiss/ CfA.

Leaking helium reveals atmosphere on rocky exoplanet

Last month, scientists found the first strong evidence for an atmosphere on a rocky planet in the habitable zone of its star. The planet, LHS 1140 b, is a super-Earth exoplanet 48 light-years away. It orbits a red dwarf star.

Scientists detected helium leaking from this world. The leaking helium means the planet must have an atmosphere. But scientists don’t know yet what the other gases are in that atmosphere.

In 2018, astronomers reported finding an exoplanet – HAT-P-11b – whose helium atmosphere is extended or puffed out, kind of like a child’s balloon.

Bottom line: Is life in helium atmospheres on exoplanets possible? A new study says that there are no barriers to life on worlds with helium-dominated atmospheres.

Source: The Viability of Life in Helium-Dominated Exoplanet Atmospheres

Via Astrobiology

Read more: 1st atmosphere detected on Earth-like, habitable-zone world

Read more: Exoplanet’s helium atmosphere is inflated like a balloon

The post Could there be life in helium atmospheres on exoplanets? first appeared on EarthSky.

from EarthSky https://ift.tt/Htzy1CN

View larger. | Artist’s concept of an exoplanet with a helium-dominated atmosphere. A new study suggests that there could be life in helium atmospheres on rocky exoplanets. Image via NASA/ JPL-Caltech.

• Could life exist on exoplanets with helium atmospheres? A new study suggests it’s possible.
• Experiments showed that helium-dominated atmospheres would be non-toxic to many types of earthly lifeforms.
• Helium atmospheres could also preserve other gases associated with life, making them easier to detect by astronomers.

Science news, night sky events and beautiful photos, all in one place. Click here to subscribe to our free daily newsletter.

Life in helium atmospheres on exoplanets?

When searching for possible signs of alien life on exoplanets, scientists tend to focus on atmospheres that might be earthlike. That is, atmospheres dominated by nitrogen, oxygen or even carbon dioxide. But there’s another possibility that has been largely overlooked. What about helium atmospheres?

Helium is the second-most abundant element in the universe. And we know there are exoplanets with helium in their atmospheres.

A new paper just released from researchers at Massachusetts Institute of Technology (MIT) in the U.S. and Wroclaw University of Science and Technology and JJ Scientific in Poland, examines the possibility of life existing in helium atmospheres. Intriguingly, the researchers found that there are no intrinsic barriers that would prevent life as we know it from being able to survive in a helium-dominated atmosphere.

The new study looks at a largely overlooked body of laboratory research on life in helium-dominated atmospheres. And the results are surprising.

The researchers published their preprint version of the paper (not yet peer-reviewed) on August 16, 2026, on arXiv.

An overlooked possibility

Scientists had largely ignored the idea that planets with helium atmospheres could support life. This was based on two key assumptions.

The first was that helium is expected to typically escape from the atmospheres of rocky planets, along with hydrogen. The second is that Earth itself doesn’t have much helium in its atmosphere. So those were the models scientists had to work with.

But the research team decided to take a closer look at the possibility of life on helium worlds. So they synthesized helium-dominated atmospheres in the laboratory. And a wide variety of organisms were subjected to that environment. These included bacteria, fungi, protozoa, microalgae, plants and animals. The results were surprising.

When the organisms had the essential metabolic requirements – the chemical processes in your body that change food into energy and build or repair cells – then they were able to tolerate and survive in the helium atmosphere.

No barriers to life

Overall, the helium did not present any barriers to life. In fact, there was no demonstrated toxicity and no fundamental barrier to metabolism, cell division, photosynthesis, nitrogen fixation or coordinated multicellular activity, including in humans. This suggests that life could survive and even thrive on planets with helium atmospheres.

And it’s seemingly because helium is chemically inert. Whether or not it would actually help life flourish is another question. But it won’t hamper or destroy it.

This is also good news for scientists trying to detect signs of life in helium atmospheres. The helium won’t destroy any biosignature gases present in the atmosphere. And it won’t obscure their spectral signatures. In fact, helium-dominated atmospheres also have low mean molecular weights and large scale heights. This actually strengthens spectral features in transmission and improves remote detectability.

Helium could help scientists find alien life

Not only does this show alien life could exist in a helium atmosphere, it could help scientists actually find it. As the paper concludes:

The possibility of helium-dominated, temperate exoplanet atmospheres asks us to widen a familiar assumption: that life-bearing atmospheres must resemble Earth’s in their bulk composition. Helium contributes little chemistry of its own, yet that very inertness allows the gases required by life to coexist within a stable atmospheric envelope, while its low molecular weight may make their spectral signatures unusually accessible.

The fact that such diverse forms of life can survive, metabolize and reproduce under helium-dominated conditions supports the inclusion of helium-dominated exoplanets among the targets in the search for life beyond Earth.

The convergence of atmospheric-evolution models, the first observations of helium around a habitable-zone rocky planet and decades of laboratory evidence establishes that helium is not an exotic obstacle to life and might in fact enable the first biosignature gas detection on a rocky world in our galaxy.

Last month, researchers reported detecting helium escaping from exoplanet LHS 1140 b. That means it must have an atmosphere, but scientists don’t yet know what other gases are in it. This is an artist’s concept of the planet in question. Image via Melissa Weiss/ CfA.

Leaking helium reveals atmosphere on rocky exoplanet

Last month, scientists found the first strong evidence for an atmosphere on a rocky planet in the habitable zone of its star. The planet, LHS 1140 b, is a super-Earth exoplanet 48 light-years away. It orbits a red dwarf star.

Scientists detected helium leaking from this world. The leaking helium means the planet must have an atmosphere. But scientists don’t know yet what the other gases are in that atmosphere.

In 2018, astronomers reported finding an exoplanet – HAT-P-11b – whose helium atmosphere is extended or puffed out, kind of like a child’s balloon.

Bottom line: Is life in helium atmospheres on exoplanets possible? A new study says that there are no barriers to life on worlds with helium-dominated atmospheres.

Source: The Viability of Life in Helium-Dominated Exoplanet Atmospheres

Via Astrobiology

Read more: 1st atmosphere detected on Earth-like, habitable-zone world

Read more: Exoplanet’s helium atmosphere is inflated like a balloon

The post Could there be life in helium atmospheres on exoplanets? first appeared on EarthSky.

from EarthSky https://ift.tt/Htzy1CN

National parks from space: How many can you name?

(1) The Landsat 8 satellite captured this view of a national park from space. The southern part of the state you see here is dominated by a River of Grass, the only place in the world where alligators and crocodiles coexist. Can you name this national park? Then read on to see how many more national parks from space you can name. All images this page via NASA Earth Observatory.

How many national parks from space can you name?

It’s National Park Week! In 2026, we celebrate the US national parks from August 22 to 30. And in honor of what has been called America’s best idea, we at EarthSky are challenging you to see how many parks you can identify from space.

America’s national parks look spectacular from the ground. But from hundreds of miles above Earth, they take on an entirely different appearance. Rivers become thin threads, mountains reveal their enormous scale and some of the landscapes we recognize instantly from photographs become surprisingly difficult to identify.

The national park image above is one that might be easy to recognize. You can see the curve of southern Florida, with Miami and its suburbs to the east and the start of the keys to the south. The green wetlands that dominate the southern portion of the state, where crocodiles mix with alligators, has been nicknamed the River of Grass. Try your hand at nine more parks below, which we’ve divided up into categories of easy, medium and hard. Good luck!

Easy: New visitor category

(2) Nearly half of this national park on the East Coast consists of Mount Desert Island, which has a dual-lobed shape as seen from above. And on this island you’ll find Cadillac Mountain, which is the first place to see sunrise in the continental U.S. during the winter months. Can you name this park?

(3) This national park might sit just offshore from one of the most populous areas in the U.S., yet its isolation gives it the nickname of Galapagos of North America. Half the park is underwater, including giant kelp forests. Meanwhile, on land you’ll find more than 145 plant and animal species found nowhere else on Earth, including the inquisitive island fox. Can you name this park?

(4) Proximity to water can certainly make it easier to identify a location from space. But in this case, the plumes of smoke and dark black substance running toward the sea should help you solve the mystery. The activity here is creating some of the newest earth on … well, Earth! Can you name this park?

Medium: Backpacker category

(5) This national park is centered around a volcano – Mount Mazama – that blew its top some 7,000 years ago. Now, rainwater has filled the space, creating the deepest lake in the U.S. at 1,943 feet. You can still see the cinder cone (partially hidden by clouds here), named Wizard Island, poking through the blue waters. Can you name this park?

(6) This majestic, snow-covered mountain is the source of 5 major rivers. That’s thanks to the 28 named glaciers on its flanks. Though it’s not expected to erupt any time soon, this is an active volcano. Can you name this park?

(7) The first clue to solving this puzzle is knowing that often, when viewing satellite photos, depressions can look like bulges and vice versa. Scientists call this the crater-dome illusion. Look closely, and you’ll see that’s not a ridge, but a muddy river that snakes through miles of weathered terrain. Can you name this park?

Hard: Park ranger category

(8) That dark cluster of mountains you see below is the only mountain range in the U.S. completely inside a single national park. This park also contains 450 species of birds, more than any other U.S. national park. Need a hint in identifying it? Trace the river below that outlines part of its border. Can you name this park?

(9) The light-colored splotch in the middle of this image shows the largest dunefield of its kind in the world. There are fossilized Ice Age human and animal footprints preserved here. And the life that resides here today can be pale in color to match its surroundings, like the bleached earless lizard. Can you name this park?

(10) This park contains rocks that are hundreds of millions of years old. The park is also home to Triple Divide Peak, where rain that falls on it can flow either to the Atlantic, Pacific or Arctic Oceans, which has earned the park the nickname Crown of the Continents. Its blue and turquoise lakes are due to ground-up rocks that scatter light. Can you name this park?

Answers for the national parks from space quiz

(1) Everglades, via Landsat 8
(2) Acadia, via Landsat 8
(3) Channel Islands, via NOAA-20 satellite
(4) Hawaii Volcanoes, via Earth Observing-1 satellite
(5) Crater Lake, via ISS
(6) Mount Rainier, via ISS
(7) Grand Canyon, via ISS
(8) Big Bend, via Landsat 7
(9) White Sands, via ISS
(10) Glacier, via Ikonos satellite

How did you score?

0-3: Hello, new visitor! Welcome to the national parks.
4-7: Congrats on attaining the level of expert backpacker!
8+: Okay, are you secretly a park ranger?

Bottom line: Take the quiz to see how many national parks from space you can name. And don’t forget to celebrate National Park Week, from August 22 to 30!

The post National parks from space: How many can you name? first appeared on EarthSky.

from EarthSky https://ift.tt/oJOYzkN

(1) The Landsat 8 satellite captured this view of a national park from space. The southern part of the state you see here is dominated by a River of Grass, the only place in the world where alligators and crocodiles coexist. Can you name this national park? Then read on to see how many more national parks from space you can name. All images this page via NASA Earth Observatory.

How many national parks from space can you name?

It’s National Park Week! In 2026, we celebrate the US national parks from August 22 to 30. And in honor of what has been called America’s best idea, we at EarthSky are challenging you to see how many parks you can identify from space.

America’s national parks look spectacular from the ground. But from hundreds of miles above Earth, they take on an entirely different appearance. Rivers become thin threads, mountains reveal their enormous scale and some of the landscapes we recognize instantly from photographs become surprisingly difficult to identify.

The national park image above is one that might be easy to recognize. You can see the curve of southern Florida, with Miami and its suburbs to the east and the start of the keys to the south. The green wetlands that dominate the southern portion of the state, where crocodiles mix with alligators, has been nicknamed the River of Grass. Try your hand at nine more parks below, which we’ve divided up into categories of easy, medium and hard. Good luck!

Easy: New visitor category

(2) Nearly half of this national park on the East Coast consists of Mount Desert Island, which has a dual-lobed shape as seen from above. And on this island you’ll find Cadillac Mountain, which is the first place to see sunrise in the continental U.S. during the winter months. Can you name this park?

(3) This national park might sit just offshore from one of the most populous areas in the U.S., yet its isolation gives it the nickname of Galapagos of North America. Half the park is underwater, including giant kelp forests. Meanwhile, on land you’ll find more than 145 plant and animal species found nowhere else on Earth, including the inquisitive island fox. Can you name this park?

(4) Proximity to water can certainly make it easier to identify a location from space. But in this case, the plumes of smoke and dark black substance running toward the sea should help you solve the mystery. The activity here is creating some of the newest earth on … well, Earth! Can you name this park?

Medium: Backpacker category

(5) This national park is centered around a volcano – Mount Mazama – that blew its top some 7,000 years ago. Now, rainwater has filled the space, creating the deepest lake in the U.S. at 1,943 feet. You can still see the cinder cone (partially hidden by clouds here), named Wizard Island, poking through the blue waters. Can you name this park?

(6) This majestic, snow-covered mountain is the source of 5 major rivers. That’s thanks to the 28 named glaciers on its flanks. Though it’s not expected to erupt any time soon, this is an active volcano. Can you name this park?

(7) The first clue to solving this puzzle is knowing that often, when viewing satellite photos, depressions can look like bulges and vice versa. Scientists call this the crater-dome illusion. Look closely, and you’ll see that’s not a ridge, but a muddy river that snakes through miles of weathered terrain. Can you name this park?

Hard: Park ranger category

(8) That dark cluster of mountains you see below is the only mountain range in the U.S. completely inside a single national park. This park also contains 450 species of birds, more than any other U.S. national park. Need a hint in identifying it? Trace the river below that outlines part of its border. Can you name this park?

(9) The light-colored splotch in the middle of this image shows the largest dunefield of its kind in the world. There are fossilized Ice Age human and animal footprints preserved here. And the life that resides here today can be pale in color to match its surroundings, like the bleached earless lizard. Can you name this park?

(10) This park contains rocks that are hundreds of millions of years old. The park is also home to Triple Divide Peak, where rain that falls on it can flow either to the Atlantic, Pacific or Arctic Oceans, which has earned the park the nickname Crown of the Continents. Its blue and turquoise lakes are due to ground-up rocks that scatter light. Can you name this park?

Answers for the national parks from space quiz

(1) Everglades, via Landsat 8
(2) Acadia, via Landsat 8
(3) Channel Islands, via NOAA-20 satellite
(4) Hawaii Volcanoes, via Earth Observing-1 satellite
(5) Crater Lake, via ISS
(6) Mount Rainier, via ISS
(7) Grand Canyon, via ISS
(8) Big Bend, via Landsat 7
(9) White Sands, via ISS
(10) Glacier, via Ikonos satellite

How did you score?

0-3: Hello, new visitor! Welcome to the national parks.
4-7: Congrats on attaining the level of expert backpacker!
8+: Okay, are you secretly a park ranger?

Bottom line: Take the quiz to see how many national parks from space you can name. And don’t forget to celebrate National Park Week, from August 22 to 30!

The post National parks from space: How many can you name? first appeared on EarthSky.

from EarthSky https://ift.tt/oJOYzkN

The return of Sirius in the morning signals seasonal change

Here’s an early morning sight you won’t want to miss. The return of Sirius and the winter constellations to the morning sky heralds a change of season. Chart via EarthSky.

In late August and early September, look for two hints of the changing season in the predawn sky: Orion the Hunter and Sirius the Dog Star.

Orion is easily recognizable by the short straight line of three bright stars that make up his Belt. The constellation rises before dawn at this time of year. And the sky’s brightest star, Sirius – also known as the Dog Star, in the constellation Canis Major the Greater Dog – follows Orion into the sky as the predawn darkness gives way to dawn.

Have you noticed a very bright, madly twinkling star in this part of the early morning sky? Many do at this time of year. That star is Sirius. It’s so bright that, when it’s low in the sky, it shines with glints of red and flashes of blue. That’s the effect of our thick atmosphere causing its light to twinkle.

You won’t see Orion and Sirius in the evening sky until northern winter (or southern summer). But presently, the Hunter and the Dog Star lord over the sky at dawn.

Stars and constellations pass behind the sun

Orion was low in the west after sunset around March and April. By June of each year, the Hunter lies behind the sun as seen from Earth. Orion only returned to visibility in Earth’s sky about a month ago. Once a constellation becomes visible again, after being behind the sun, it always appears in the east before sunrise.

That’s because – as Earth moves around the sun – all stars rise two hours earlier with each passing month. So Orion is now higher at dawn than it was a month ago.

As seen from the Northern Hemisphere, Orion precedes Sirius into the sky. After Orion first appears at dawn, you can count on Sirius to appear in the morning sky a few weeks later.

View at EarthSky Community Photos. | Jeremy Evans caught this image on January 22, 2026, in California and wrote: “Orion and Sirius over the Sierra Nevada around midnight. Cold foggy night, temperature was 8 degrees F. Taken from backyard using snowshoes to get to the photo spot.” Note the brightest star at the left is Sirius. Thank you, Jeremy!

The heliacal rising of Sirius

Now will be a good time to look for the heliacal rising of Sirius. In other words, what is the first date that you can see Sirius, with the unaided eye, in your morning sky? It depends on your latitude.

Below are a couple of graphs showing when you can expect to first see Sirius in your eastern predawn sky. They are designed for average eyesight, average weather and from near sea level.

The heliacal rising of Sirius from latitudes 20 degrees south to 70 degrees north. Philadelphia, for example, is at 40 degrees north latitude, so it will see Sirius reappear in the morning sky around August 17. Based on calculations by Culture Diff’. Graph via Don Machholz.

The heliacal rising of Sirius from north latitudes 10 degrees to 60 degrees. Based on calculations by Culture Diff’. Graph via Don Machholz.

The return of Sirius and the colors of the stars

With Sirius and the stars of Orion low in your sky, you might notice that their light shimmers in various colors. But it’s not the stars that are changing; this is the prismatic effect of Earth’s atmosphere. As seen through a greater-than-usual thickness of atmosphere in the direction of the horizon, the mostly white light of Sirius can be broken up into striking colors on a summer morning.

But stars can be intrinsically colorful, too. Be sure to notice the reddish color of Betelgeuse when you watch Orion rise in these late summer months.

View at EarthSky Community Photos. | Daniel Friedman captured this beautiful shot from Montauk, New York, in December 2020. Note how bright Sirius is on the left, and how its color contrasts with the star Betelgeuse in the top left corner. Daniel wrote: “Out on the beach late with no one around for miles. Never captured a bolt like this and have been chasing meteor showers for years and years.” Thank you, Daniel!

Bottom line: A sign of the changing season is the return of Sirius before sunup. Be the first from your latitude to see Sirius in the morning sky.

Enjoying EarthSky so far? Sign up for our free daily newsletter today!

Help support EarthSky! Check out the EarthSky store for fun astronomy gifts and tools for all ages!

The post The return of Sirius in the morning signals seasonal change first appeared on EarthSky.

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Here’s an early morning sight you won’t want to miss. The return of Sirius and the winter constellations to the morning sky heralds a change of season. Chart via EarthSky.

In late August and early September, look for two hints of the changing season in the predawn sky: Orion the Hunter and Sirius the Dog Star.

Orion is easily recognizable by the short straight line of three bright stars that make up his Belt. The constellation rises before dawn at this time of year. And the sky’s brightest star, Sirius – also known as the Dog Star, in the constellation Canis Major the Greater Dog – follows Orion into the sky as the predawn darkness gives way to dawn.

Have you noticed a very bright, madly twinkling star in this part of the early morning sky? Many do at this time of year. That star is Sirius. It’s so bright that, when it’s low in the sky, it shines with glints of red and flashes of blue. That’s the effect of our thick atmosphere causing its light to twinkle.

You won’t see Orion and Sirius in the evening sky until northern winter (or southern summer). But presently, the Hunter and the Dog Star lord over the sky at dawn.

Stars and constellations pass behind the sun

Orion was low in the west after sunset around March and April. By June of each year, the Hunter lies behind the sun as seen from Earth. Orion only returned to visibility in Earth’s sky about a month ago. Once a constellation becomes visible again, after being behind the sun, it always appears in the east before sunrise.

That’s because – as Earth moves around the sun – all stars rise two hours earlier with each passing month. So Orion is now higher at dawn than it was a month ago.

As seen from the Northern Hemisphere, Orion precedes Sirius into the sky. After Orion first appears at dawn, you can count on Sirius to appear in the morning sky a few weeks later.

View at EarthSky Community Photos. | Jeremy Evans caught this image on January 22, 2026, in California and wrote: “Orion and Sirius over the Sierra Nevada around midnight. Cold foggy night, temperature was 8 degrees F. Taken from backyard using snowshoes to get to the photo spot.” Note the brightest star at the left is Sirius. Thank you, Jeremy!

The heliacal rising of Sirius

Now will be a good time to look for the heliacal rising of Sirius. In other words, what is the first date that you can see Sirius, with the unaided eye, in your morning sky? It depends on your latitude.

Below are a couple of graphs showing when you can expect to first see Sirius in your eastern predawn sky. They are designed for average eyesight, average weather and from near sea level.

The heliacal rising of Sirius from latitudes 20 degrees south to 70 degrees north. Philadelphia, for example, is at 40 degrees north latitude, so it will see Sirius reappear in the morning sky around August 17. Based on calculations by Culture Diff’. Graph via Don Machholz.

The heliacal rising of Sirius from north latitudes 10 degrees to 60 degrees. Based on calculations by Culture Diff’. Graph via Don Machholz.

The return of Sirius and the colors of the stars

With Sirius and the stars of Orion low in your sky, you might notice that their light shimmers in various colors. But it’s not the stars that are changing; this is the prismatic effect of Earth’s atmosphere. As seen through a greater-than-usual thickness of atmosphere in the direction of the horizon, the mostly white light of Sirius can be broken up into striking colors on a summer morning.

But stars can be intrinsically colorful, too. Be sure to notice the reddish color of Betelgeuse when you watch Orion rise in these late summer months.

View at EarthSky Community Photos. | Daniel Friedman captured this beautiful shot from Montauk, New York, in December 2020. Note how bright Sirius is on the left, and how its color contrasts with the star Betelgeuse in the top left corner. Daniel wrote: “Out on the beach late with no one around for miles. Never captured a bolt like this and have been chasing meteor showers for years and years.” Thank you, Daniel!

Bottom line: A sign of the changing season is the return of Sirius before sunup. Be the first from your latitude to see Sirius in the morning sky.

Enjoying EarthSky so far? Sign up for our free daily newsletter today!

Help support EarthSky! Check out the EarthSky store for fun astronomy gifts and tools for all ages!

The post The return of Sirius in the morning signals seasonal change first appeared on EarthSky.

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Nancy Grace Roman Space Telescope launches Sunday!

On June 21, 2026, the Nancy Grace Roman Space Telescope arrived at Florida’s Kennedy Space Center on NASA’s enormous Pegasus barge (left) in preparation for its August 30 launch. Image via Amber Jean Notvest/ NASA.

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The Nancy Grace Roman Space Telescope launches on Sunday

The Nancy Grace Roman Space Telescope is set to launch no earlier than 6:26 a.m. CDT on Sunday, August 30, 2026. The launch will be on a SpaceX Falcon Heavy rocket from Launch Complex 39A at Kennedy Space Center. Amazingly, the space telescope is eight months ahead of schedule!

On June 21, 2026, the Nancy Grace Roman Space Telescope arrived at Kennedy Space Center in Florida ahead of its launch. It completed testing at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, before being loaded on NASA’s Pegasus barge for its shipment to Florida. After additional testing at Kennedy Space Center, the telescope is ready for its journey to L2, or the second sun-Earth Lagrange point.

You may already be familiar with this location because the James Webb Space Telescope is also there, sending back infrared images of the universe. The Roman telescope also has infrared eyes. NASA said:

Roman’s wide field of view and rapid survey capabilities will reveal billions of galaxies, hundreds of thousands of new exoplanets, hundreds of black holes, and will provide vast volumes of daily data for astronomers to study.

The Nancy Grace Roman Space Telescope is complete

NASA said back on December 4, 2025, that the construction of the Nancy Grace Roman Space Telescope was complete. Julie McEnery, Roman’s senior project scientist at NASA Goddard, said:

With Roman’s construction complete, we are poised at the brink of unfathomable scientific discovery. In the mission’s first five years, it’s expected to unveil more than 100,000 distant worlds, hundreds of millions of stars, and billions of galaxies. We stand to learn a tremendous amount of new information about the universe very rapidly after Roman launches.

The fully assembled Nancy Grace Roman Space Telescope. Image via Jolearra Tshiteya/ NASA.

The Nancy Grace Roman Space Telescope by the numbers. Graphic via NASA/ Goddard Space Flight Center.

Meet the Nancy Grace Roman Space Telescope

Remember what astronomical images were like before we had the Hubble Space Telescope? Hubble was the first large optical telescope to be launched into space, above Earth’s obscuring atmosphere. And it fundamentally changed our view of the cosmos. Astronomers say the Nancy Grace Roman Space Telescope will do that, too, giving us a view of the universe we’ve never had before. The telescope will have a primary mirror of 7.9 feet in diameter (2.4 meters). That’s the same size as Hubble. But a single image from the Nancy Grace Roman Space Telescope will equal the sky coverage of 100 Hubble images.

Scientists expect the telescope to answer fundamental questions about distant planets orbiting stars in our Milky Way galaxy, about the dark energy we haven’t yet detected directly but believe makes up a substantial portion of our cosmos … and about what astronomers call the cosmic dawn.

The telescope’s Wide Field Instrument (WFI), its primary instrument, will have a field of view 100 times greater than Hubble’s infrared instrument. Roman’s large field of view means it can capture more sky in less time. The Wide Field Instrument will scan the Milky Way for exoplanets, or planets orbiting distant stars. Over the past 30 years, since the early 1990s until now, we’ve discovered more than 5,000 exoplanets. The Nancy Grace Roman Space Telescope is expected to increase that number to some 100,000 exoplanets in the next five years.

Roman’s other instrument is the Coronagraph Instrument. The Coronagraph Instrument will perform high-contrast imaging and spectroscopy to gather more knowledge of individual exoplanets. More on the coronagraph below.

Interview with Néstor Espinoza

Watch this 52-second clip of astronomer Néstor Espinoza of the Space Telescope Science Institute talking with EarthSky’s Deborah Byrd. Néstor told us this telescope should increase the number of known exoplanets – or planets orbiting distant suns – from 5,000 now to 100,000 in just 5 years!

The Roman telescope’s 100,000 new exoplanets

The Roman space telescope will survey our galaxy, taking observations every 15 minutes for more than a year. What a mass of data it’ll collect in just that first year! The data will enable astronomers to track the brightness changes in stars, which could lead to discoveries of exoplanets, rogue planets, isolated black holes and more.

So how will the Roman space telescope find its 100,000 exoplanets? With the aid of the Roman Coronagraph, the first high-contrast active wavefront-control coronagraph to fly in space. NASA said:

The Roman Coronagraph will advance scientists’ ability to directly image planets and disks around other stars. Coronagraphs work by blocking light from a bright object, like a star, so that the observer can more easily see a faint object, like a planet [next to the bright object].

The Roman Coronagraph is designed to detect planets 100 million times fainter than their stars, or 100 to 1,000 times better than existing space-based coronagraphs.

The Roman Coronagraph will be capable of directly imaging reflected starlight from a planet akin to Jupiter in size, temperature and distance from its parent star.

Artist’s concept of the Nancy Grace Roman Space Telescope. Image via NASA.

The Roman telescope and the cosmic dawn

After the Big Bang that set our universe into motion, the cosmos was dark for some 380,000 to 200 million years. Yes, dark. Even though stars had already begun to shine, neutral atoms would absorb their light, leaving the cosmos in a kind of obscuring fog. Then neutral atoms began to break apart, and the fog began to lift. The light of stars broke through and began traveling throughout space. Astronomers call this transition from dark to light the cosmic dawn. Takahiro Morishita of Caltech said:

Roman will excel at finding the building blocks of cosmic structures like galaxy clusters that later form. It will quickly identify the densest regions, where more ‘fog’ is being cleared, making Roman a key mission to probe early galaxy evolution and the cosmic dawn.

Roman’s wide field of view will help determine how common quasars are and whether certain types of galaxies played a larger role in clearing the fog. It will also look for “cosmic daybreakers” that illuminated our universe.

Artist’s concept of the cosmic dawn. This is how the universe may have looked at less than a billion years old. Image via NASA/ ESA/ A. Schaller (for STScI).

The Roman space telescope and dark energy

Dark energy is a mysterious force that makes up about 68% of the total energy content of our universe. Dark energy is responsible for the acceleration of our expanding universe. Roman will help astronomers understand just what dark energy is by taking a closer look at how the universe has evolved. Roman’s wide field will allow us a bigger picture of the universe. Mapping the distribution of matter and measuring distant supernovae will help show how dark energy might have changed over time.

In the universe’s past, expansion occurred at a slower rate than we see in our universe today. Dark energy is behind the accelerated expansion. Image via NASA Scientific Visualization Studio.

Who was Nancy Grace Roman?

Nancy Grace Roman has the honorary title of Mother of the Hubble Space Telescope. Born in 1925, Roman became one of the few female astronomers in a male-dominated science. Among other accomplishments, she became the first female executive at NASA and NASA’s first Chief of Astronomy. She earned her nickname by helping get the Hubble Space Telescope approved by Congress. Roman was most excited for Hubble’s discoveries on dark energy. The telescope that will now bear Roman’s name will increase our understanding of dark energy, the universe and our place in it.

Read more about Nancy Grace Roman

Nancy Grace Roman, “mother of the Hubble space telescope,” during her career at NASA. Image via NASA.

Bottom line: The launch of the Nancy Grace Roman Space Telescope is scheduled for launch Sunday morning, August 30, from the Kennedy Space Center. The mission is eight months ahead of schedule.

Via NASA

Via NASA JPL

Read more: 3 years of the Webb telescope: Here’s what it’s discovered

Read more: Alien life? Mammoth new telescope could find it in hours

The post Nancy Grace Roman Space Telescope launches Sunday! first appeared on EarthSky.

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On June 21, 2026, the Nancy Grace Roman Space Telescope arrived at Florida’s Kennedy Space Center on NASA’s enormous Pegasus barge (left) in preparation for its August 30 launch. Image via Amber Jean Notvest/ NASA.

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The Nancy Grace Roman Space Telescope launches on Sunday

The Nancy Grace Roman Space Telescope is set to launch no earlier than 6:26 a.m. CDT on Sunday, August 30, 2026. The launch will be on a SpaceX Falcon Heavy rocket from Launch Complex 39A at Kennedy Space Center. Amazingly, the space telescope is eight months ahead of schedule!

On June 21, 2026, the Nancy Grace Roman Space Telescope arrived at Kennedy Space Center in Florida ahead of its launch. It completed testing at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, before being loaded on NASA’s Pegasus barge for its shipment to Florida. After additional testing at Kennedy Space Center, the telescope is ready for its journey to L2, or the second sun-Earth Lagrange point.

You may already be familiar with this location because the James Webb Space Telescope is also there, sending back infrared images of the universe. The Roman telescope also has infrared eyes. NASA said:

Roman’s wide field of view and rapid survey capabilities will reveal billions of galaxies, hundreds of thousands of new exoplanets, hundreds of black holes, and will provide vast volumes of daily data for astronomers to study.

The Nancy Grace Roman Space Telescope is complete

NASA said back on December 4, 2025, that the construction of the Nancy Grace Roman Space Telescope was complete. Julie McEnery, Roman’s senior project scientist at NASA Goddard, said:

With Roman’s construction complete, we are poised at the brink of unfathomable scientific discovery. In the mission’s first five years, it’s expected to unveil more than 100,000 distant worlds, hundreds of millions of stars, and billions of galaxies. We stand to learn a tremendous amount of new information about the universe very rapidly after Roman launches.

The fully assembled Nancy Grace Roman Space Telescope. Image via Jolearra Tshiteya/ NASA.

The Nancy Grace Roman Space Telescope by the numbers. Graphic via NASA/ Goddard Space Flight Center.

Meet the Nancy Grace Roman Space Telescope

Remember what astronomical images were like before we had the Hubble Space Telescope? Hubble was the first large optical telescope to be launched into space, above Earth’s obscuring atmosphere. And it fundamentally changed our view of the cosmos. Astronomers say the Nancy Grace Roman Space Telescope will do that, too, giving us a view of the universe we’ve never had before. The telescope will have a primary mirror of 7.9 feet in diameter (2.4 meters). That’s the same size as Hubble. But a single image from the Nancy Grace Roman Space Telescope will equal the sky coverage of 100 Hubble images.

Scientists expect the telescope to answer fundamental questions about distant planets orbiting stars in our Milky Way galaxy, about the dark energy we haven’t yet detected directly but believe makes up a substantial portion of our cosmos … and about what astronomers call the cosmic dawn.

The telescope’s Wide Field Instrument (WFI), its primary instrument, will have a field of view 100 times greater than Hubble’s infrared instrument. Roman’s large field of view means it can capture more sky in less time. The Wide Field Instrument will scan the Milky Way for exoplanets, or planets orbiting distant stars. Over the past 30 years, since the early 1990s until now, we’ve discovered more than 5,000 exoplanets. The Nancy Grace Roman Space Telescope is expected to increase that number to some 100,000 exoplanets in the next five years.

Roman’s other instrument is the Coronagraph Instrument. The Coronagraph Instrument will perform high-contrast imaging and spectroscopy to gather more knowledge of individual exoplanets. More on the coronagraph below.

Interview with Néstor Espinoza

Watch this 52-second clip of astronomer Néstor Espinoza of the Space Telescope Science Institute talking with EarthSky’s Deborah Byrd. Néstor told us this telescope should increase the number of known exoplanets – or planets orbiting distant suns – from 5,000 now to 100,000 in just 5 years!

The Roman telescope’s 100,000 new exoplanets

The Roman space telescope will survey our galaxy, taking observations every 15 minutes for more than a year. What a mass of data it’ll collect in just that first year! The data will enable astronomers to track the brightness changes in stars, which could lead to discoveries of exoplanets, rogue planets, isolated black holes and more.

So how will the Roman space telescope find its 100,000 exoplanets? With the aid of the Roman Coronagraph, the first high-contrast active wavefront-control coronagraph to fly in space. NASA said:

The Roman Coronagraph will advance scientists’ ability to directly image planets and disks around other stars. Coronagraphs work by blocking light from a bright object, like a star, so that the observer can more easily see a faint object, like a planet [next to the bright object].

The Roman Coronagraph is designed to detect planets 100 million times fainter than their stars, or 100 to 1,000 times better than existing space-based coronagraphs.

The Roman Coronagraph will be capable of directly imaging reflected starlight from a planet akin to Jupiter in size, temperature and distance from its parent star.

Artist’s concept of the Nancy Grace Roman Space Telescope. Image via NASA.

The Roman telescope and the cosmic dawn

After the Big Bang that set our universe into motion, the cosmos was dark for some 380,000 to 200 million years. Yes, dark. Even though stars had already begun to shine, neutral atoms would absorb their light, leaving the cosmos in a kind of obscuring fog. Then neutral atoms began to break apart, and the fog began to lift. The light of stars broke through and began traveling throughout space. Astronomers call this transition from dark to light the cosmic dawn. Takahiro Morishita of Caltech said:

Roman will excel at finding the building blocks of cosmic structures like galaxy clusters that later form. It will quickly identify the densest regions, where more ‘fog’ is being cleared, making Roman a key mission to probe early galaxy evolution and the cosmic dawn.

Roman’s wide field of view will help determine how common quasars are and whether certain types of galaxies played a larger role in clearing the fog. It will also look for “cosmic daybreakers” that illuminated our universe.

Artist’s concept of the cosmic dawn. This is how the universe may have looked at less than a billion years old. Image via NASA/ ESA/ A. Schaller (for STScI).

The Roman space telescope and dark energy

Dark energy is a mysterious force that makes up about 68% of the total energy content of our universe. Dark energy is responsible for the acceleration of our expanding universe. Roman will help astronomers understand just what dark energy is by taking a closer look at how the universe has evolved. Roman’s wide field will allow us a bigger picture of the universe. Mapping the distribution of matter and measuring distant supernovae will help show how dark energy might have changed over time.

In the universe’s past, expansion occurred at a slower rate than we see in our universe today. Dark energy is behind the accelerated expansion. Image via NASA Scientific Visualization Studio.

Who was Nancy Grace Roman?

Nancy Grace Roman has the honorary title of Mother of the Hubble Space Telescope. Born in 1925, Roman became one of the few female astronomers in a male-dominated science. Among other accomplishments, she became the first female executive at NASA and NASA’s first Chief of Astronomy. She earned her nickname by helping get the Hubble Space Telescope approved by Congress. Roman was most excited for Hubble’s discoveries on dark energy. The telescope that will now bear Roman’s name will increase our understanding of dark energy, the universe and our place in it.

Read more about Nancy Grace Roman

Nancy Grace Roman, “mother of the Hubble space telescope,” during her career at NASA. Image via NASA.

Bottom line: The launch of the Nancy Grace Roman Space Telescope is scheduled for launch Sunday morning, August 30, from the Kennedy Space Center. The mission is eight months ahead of schedule.

Via NASA

Via NASA JPL

Read more: 3 years of the Webb telescope: Here’s what it’s discovered

Read more: Alien life? Mammoth new telescope could find it in hours

The post Nancy Grace Roman Space Telescope launches Sunday! first appeared on EarthSky.

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Pluto demoted to dwarf planet 20 years ago today

Pluto backlit, via New Horizons spacecraft on July 14, 2015. Image via NASA/ JHUAPL/ SwRI.

Dwarf planet Pluto

On August 24, 2006, the International Astronomical Union (IAU) announced it had re-classified Pluto as a dwarf planet. From 1930 until that day, Pluto had been considered a normal planet, and the outermost world of the solar system. As technology advanced, though, astronomers began to see fainter and fainter objects in our neighborhood. That led them to recognize Pluto as only the largest of many small bodies in the outer solar system.

Now Pluto is known as a dwarf planet, and Neptune – 8th world from the sun – is considered the outermost major planet. It all came about because the IAU had formulated a new definition of what it means to be a planet.

The public and even some astronomers didn’t initially take it lightly. Some declared they would still consider Pluto a planet. The word ‘plutoed‘ – meaning to demote or devalue something – entered the global lexicon. Nowadays, though, it seems most have accepted the logic of Pluto’s re-classification… or, at least, we don’t hear as much of an uproar about it as we used to.

Why did Pluto change status?

Prior to 2006, astronomers hadn’t gotten around to establishing clear standards for categorizing a solar system “planet” versus a “dwarf planet.”

They began to see a need when many small bodies – such as Haumea and Makemake – began to be discovered in the outer solar system. Eris, also considered a dwarf planet, has even more mass than Pluto (though it’s not quite as large). So if Pluto is a planet, why shouldn’t Eris be granted planet status as well? That was the question the IAU asked itself, which led to its formation of a Planet Definition Committee and ultimately the 2006 decision.

The committee had a few possible roads to travel down. One would be to choose a size or mass limit that would make Pluto remain a planet. That would mean that Eris and Ceres – the largest body in the inner solar system’s asteroid belt – would become planets, too. This was the solution of some IAU committee members, and it looked like it might be implemented for a while.

Another option for the IAU might have been to define the concept of a planet without any specific logic: Earth is a planet, Pluto is a planet, but Eris is not just because. But would that have been very scientific?

Meet the The Planet Definition Committee of the International Astronomical Union. This group made the final decision to “demote” Pluto to dwarf planet status. But, even within the committee, not all initially agreed. Image via IAU.

New planetary classifications

On August 24, 2006, the IAU announced its solution. It decided to create a scientific definition of what it means to be a planet. And that definition excluded Pluto from major planet status. Here’s the definition:

A planet is a celestial body that
(a) is in orbit around the Sun,
(b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and
(c) has cleared the neighborhood around its orbit.

It’s “c” that causes Pluto to fail as a planet, according to the IAU. For an object to be a major planet, according to this definition, it must be the dominant gravitational object in its orbit. It must either sling other objects away or merge with them.

Pluto is only 0.07 times the mass of the objects in its orbit. Meanwhile, Earth is 1.7 million times the mass of the objects in its orbit.

When Pluto lost its full planet status, it was revealed as one of the world’s most beloved astronomical objects. So it was fitting that New Horizons – the first spacecraft ever to visit Pluto – discovered a heart-shaped region on it in 2015. Image taken 280,000 miles (450,000 km) from Pluto, via NASA/ JHUAPL/ SwRI.

Pluto hasn’t cleared its neighborhood

On that fateful day – August 24, 2006 – the IAU also created a new category of celestial objects for Pluto and all Pluto-like objects:

A “dwarf planet” is a celestial body that
(a) is in orbit around the sun,
(b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape,
(c) has not cleared the neighborhood around its orbit, and
(d) is not a satellite.

How many dwarf planets are there? According to this page by planetary astronomer Mike Brown of CalTech, as of November 25, 2025, there are:

10 objects which are nearly certainly dwarf planets,
27 objects which are highly likely to be dwarf planets,
68 objects which are likely to be dwarf planets,
130 objects which are probably dwarf planets, and
741 objects which are possibly dwarf planets.

New Horizons captured this image just 15 minutes after its closest approach to Pluto on July 14, 2015, as the spacecraft looked back toward the sun. This near-sunset view shows Pluto’s rugged, icy mountains and flat ice plains, plus haze layers in Pluto’s tenuous but distended atmosphere. The image was taken from a distance of 11,000 miles (18,000 km); the scene is 780 miles (1,250 km) wide. Image via NASA/ JHUAPL/ SwRI.

Hundreds of dwarf planets?

Astronomers believe there may be hundreds more undiscovered dwarf planets in the Kuiper Belt of the outer solar system. There may be up to 10,000 in the region beyond.

More about the Kuiper Belt: https://t.co/qNCG1GvgeP https://t.co/kPGvZtR4IY pic.twitter.com/FYX5Cv2PDD

— NASA Solar System (@NASASolarSystem) February 20, 2024

Not a new idea

By the way, it’s not common knowledge that many astronomers started out being quite careful about their use of the word “planet” with respect to Pluto. In 1932, for example, only two years after American astronomer Clyde Tombaugh discovered Pluto, another astronomer, Armin Otto Leuschner, wrote in a journal article:

You may observe that with extreme conservatism I am still referring to Pluto as an object rather than as a planet. There is every probability that it is a planet, as is now universally concluded, from available material … So far only an upper limit for the mass of Pluto … has been established, and such a mass is believed from gravitational considerations to be too small to affect the motions of Uranus and Neptune sufficiently … There is also a remote chance that later investigations will render its mass comparable to that of comets.

Pluto might never have been called a planet at all

Recall why astronomers began searching for Pluto in the first place. They expected to find an object large enough to gravitationally disturb the orbit of Neptune. If Pluto had been discovered a decade or so later, when Edgeworth speculated about the existence of the Kuiper Belt, it might have never been awarded the status of planet.

As it was, like it or not, Pluto became the world’s eye-opener when it came to the classification of solar system objects.

Bottom line: August 24 is the anniversary of Pluto’s demotion to dwarf planet status. The International Astronomical Union demoted Pluto largely because it is has not “cleared the neighborhood around its orbit.”

Read more about Pluto here

The IAU talks about its decision to demote Pluto here

Read more: Pluto terrain in rainbow colors

The post Pluto demoted to dwarf planet 20 years ago today first appeared on EarthSky.

from EarthSky https://ift.tt/1TvH0wb

Pluto backlit, via New Horizons spacecraft on July 14, 2015. Image via NASA/ JHUAPL/ SwRI.

Dwarf planet Pluto

On August 24, 2006, the International Astronomical Union (IAU) announced it had re-classified Pluto as a dwarf planet. From 1930 until that day, Pluto had been considered a normal planet, and the outermost world of the solar system. As technology advanced, though, astronomers began to see fainter and fainter objects in our neighborhood. That led them to recognize Pluto as only the largest of many small bodies in the outer solar system.

Now Pluto is known as a dwarf planet, and Neptune – 8th world from the sun – is considered the outermost major planet. It all came about because the IAU had formulated a new definition of what it means to be a planet.

The public and even some astronomers didn’t initially take it lightly. Some declared they would still consider Pluto a planet. The word ‘plutoed‘ – meaning to demote or devalue something – entered the global lexicon. Nowadays, though, it seems most have accepted the logic of Pluto’s re-classification… or, at least, we don’t hear as much of an uproar about it as we used to.

Why did Pluto change status?

Prior to 2006, astronomers hadn’t gotten around to establishing clear standards for categorizing a solar system “planet” versus a “dwarf planet.”

They began to see a need when many small bodies – such as Haumea and Makemake – began to be discovered in the outer solar system. Eris, also considered a dwarf planet, has even more mass than Pluto (though it’s not quite as large). So if Pluto is a planet, why shouldn’t Eris be granted planet status as well? That was the question the IAU asked itself, which led to its formation of a Planet Definition Committee and ultimately the 2006 decision.

The committee had a few possible roads to travel down. One would be to choose a size or mass limit that would make Pluto remain a planet. That would mean that Eris and Ceres – the largest body in the inner solar system’s asteroid belt – would become planets, too. This was the solution of some IAU committee members, and it looked like it might be implemented for a while.

Another option for the IAU might have been to define the concept of a planet without any specific logic: Earth is a planet, Pluto is a planet, but Eris is not just because. But would that have been very scientific?

Meet the The Planet Definition Committee of the International Astronomical Union. This group made the final decision to “demote” Pluto to dwarf planet status. But, even within the committee, not all initially agreed. Image via IAU.

New planetary classifications

On August 24, 2006, the IAU announced its solution. It decided to create a scientific definition of what it means to be a planet. And that definition excluded Pluto from major planet status. Here’s the definition:

A planet is a celestial body that
(a) is in orbit around the Sun,
(b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and
(c) has cleared the neighborhood around its orbit.

It’s “c” that causes Pluto to fail as a planet, according to the IAU. For an object to be a major planet, according to this definition, it must be the dominant gravitational object in its orbit. It must either sling other objects away or merge with them.

Pluto is only 0.07 times the mass of the objects in its orbit. Meanwhile, Earth is 1.7 million times the mass of the objects in its orbit.

When Pluto lost its full planet status, it was revealed as one of the world’s most beloved astronomical objects. So it was fitting that New Horizons – the first spacecraft ever to visit Pluto – discovered a heart-shaped region on it in 2015. Image taken 280,000 miles (450,000 km) from Pluto, via NASA/ JHUAPL/ SwRI.

Pluto hasn’t cleared its neighborhood

On that fateful day – August 24, 2006 – the IAU also created a new category of celestial objects for Pluto and all Pluto-like objects:

A “dwarf planet” is a celestial body that
(a) is in orbit around the sun,
(b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape,
(c) has not cleared the neighborhood around its orbit, and
(d) is not a satellite.

How many dwarf planets are there? According to this page by planetary astronomer Mike Brown of CalTech, as of November 25, 2025, there are:

10 objects which are nearly certainly dwarf planets,
27 objects which are highly likely to be dwarf planets,
68 objects which are likely to be dwarf planets,
130 objects which are probably dwarf planets, and
741 objects which are possibly dwarf planets.

New Horizons captured this image just 15 minutes after its closest approach to Pluto on July 14, 2015, as the spacecraft looked back toward the sun. This near-sunset view shows Pluto’s rugged, icy mountains and flat ice plains, plus haze layers in Pluto’s tenuous but distended atmosphere. The image was taken from a distance of 11,000 miles (18,000 km); the scene is 780 miles (1,250 km) wide. Image via NASA/ JHUAPL/ SwRI.

Hundreds of dwarf planets?

Astronomers believe there may be hundreds more undiscovered dwarf planets in the Kuiper Belt of the outer solar system. There may be up to 10,000 in the region beyond.

More about the Kuiper Belt: https://t.co/qNCG1GvgeP https://t.co/kPGvZtR4IY pic.twitter.com/FYX5Cv2PDD

— NASA Solar System (@NASASolarSystem) February 20, 2024

Not a new idea

By the way, it’s not common knowledge that many astronomers started out being quite careful about their use of the word “planet” with respect to Pluto. In 1932, for example, only two years after American astronomer Clyde Tombaugh discovered Pluto, another astronomer, Armin Otto Leuschner, wrote in a journal article:

You may observe that with extreme conservatism I am still referring to Pluto as an object rather than as a planet. There is every probability that it is a planet, as is now universally concluded, from available material … So far only an upper limit for the mass of Pluto … has been established, and such a mass is believed from gravitational considerations to be too small to affect the motions of Uranus and Neptune sufficiently … There is also a remote chance that later investigations will render its mass comparable to that of comets.

Pluto might never have been called a planet at all

Recall why astronomers began searching for Pluto in the first place. They expected to find an object large enough to gravitationally disturb the orbit of Neptune. If Pluto had been discovered a decade or so later, when Edgeworth speculated about the existence of the Kuiper Belt, it might have never been awarded the status of planet.

As it was, like it or not, Pluto became the world’s eye-opener when it came to the classification of solar system objects.

Bottom line: August 24 is the anniversary of Pluto’s demotion to dwarf planet status. The International Astronomical Union demoted Pluto largely because it is has not “cleared the neighborhood around its orbit.”

Read more about Pluto here

The IAU talks about its decision to demote Pluto here

Read more: Pluto terrain in rainbow colors

The post Pluto demoted to dwarf planet 20 years ago today first appeared on EarthSky.

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1st photo of Earth from the moon 60 years ago

Lunar Orbiter 1 captured this 1st photo of Earth from the moon on August 23, 1966. See a version of this image restored with modern photographic techniques, below. Image via NASA/Lunar Orbiter 1.

You deserve a daily dose of good news. For the latest in science and the night sky, subscribe to EarthSky’s free daily newsletter.

1st photo of Earth from the moon

On August 23, 1966, Lunar Orbiter 1 took the 1st-ever photo of the Earth from the moon. It shows half of Earth, shot with 1960s technology, seen from the moon’s distance of 236,000 miles (380,000 km). And in the image, you can see the Earth from Istanbul to Cape Town with areas east shrouded in night. The image isn’t very detailed. But it’s mind-boggling to think about. What a contrast with NASA’s recent Artemis 2 mission that sent astronauts to orbit the moon for the first time in over 50 years! See Artemis 2 images here.

Lunar Orbiter 1 was one of five Lunar Orbiters that NASA sent to the moon in the 1960s. The Lunar Orbiter’s priority was to take photographs of the moon. That’s because NASA was preparing for the first manned Apollo mission, which came three years later. Read about the Lunar Orbiter missions, 1966-1967.

As you can see, the photo taken in 1966 reveals no detail on Earth’s surface.

But, surely, this photo stunned those on Earth who finally saw our home planet from the moon.

Years later, a digitally enhanced version

Then, in 2008, NASA released a newly restored version of the original 1966 image of Earth. NASA used refurbished machinery and modern digital technology. Consequently, the new image is higher resolution than what was possible when it was originally taken. Wow! What a difference.

The impressive restored image of the Earth from the moon is below.

In 2008, NASA restored this 1st image of Earth from the moon. Lunar Orbiter 1 took the original image. NASA used photographic techniques that were not available when that early spacecraft originally acquired this historic photo. Read more about this photo from NASA.

Bottom line: As NASA plans to land astronauts on the moon with the Artemis IV mission in 2028, it’s fun to see this 1st-ever photo of Earth from the moon, taken on August 23, 1966.

NASA releases 12,000 Artemis pics! See our faves here

The post 1st photo of Earth from the moon 60 years ago first appeared on EarthSky.

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Lunar Orbiter 1 captured this 1st photo of Earth from the moon on August 23, 1966. See a version of this image restored with modern photographic techniques, below. Image via NASA/Lunar Orbiter 1.

You deserve a daily dose of good news. For the latest in science and the night sky, subscribe to EarthSky’s free daily newsletter.

1st photo of Earth from the moon

On August 23, 1966, Lunar Orbiter 1 took the 1st-ever photo of the Earth from the moon. It shows half of Earth, shot with 1960s technology, seen from the moon’s distance of 236,000 miles (380,000 km). And in the image, you can see the Earth from Istanbul to Cape Town with areas east shrouded in night. The image isn’t very detailed. But it’s mind-boggling to think about. What a contrast with NASA’s recent Artemis 2 mission that sent astronauts to orbit the moon for the first time in over 50 years! See Artemis 2 images here.

Lunar Orbiter 1 was one of five Lunar Orbiters that NASA sent to the moon in the 1960s. The Lunar Orbiter’s priority was to take photographs of the moon. That’s because NASA was preparing for the first manned Apollo mission, which came three years later. Read about the Lunar Orbiter missions, 1966-1967.

As you can see, the photo taken in 1966 reveals no detail on Earth’s surface.

But, surely, this photo stunned those on Earth who finally saw our home planet from the moon.

Years later, a digitally enhanced version

Then, in 2008, NASA released a newly restored version of the original 1966 image of Earth. NASA used refurbished machinery and modern digital technology. Consequently, the new image is higher resolution than what was possible when it was originally taken. Wow! What a difference.

The impressive restored image of the Earth from the moon is below.

In 2008, NASA restored this 1st image of Earth from the moon. Lunar Orbiter 1 took the original image. NASA used photographic techniques that were not available when that early spacecraft originally acquired this historic photo. Read more about this photo from NASA.

Bottom line: As NASA plans to land astronauts on the moon with the Artemis IV mission in 2028, it’s fun to see this 1st-ever photo of Earth from the moon, taken on August 23, 1966.

NASA releases 12,000 Artemis pics! See our faves here

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Sagittarius the Archer is home to deep-sky wonders

Sagittarius the Archer contains a Teapot shape. It’s located in the direction of the center of our Milky Way galaxy. If you live far enough south – say at least at latitudes like those in the southern U.S., or farther south – you might spot the arcing shape of Corona Australis near Sagittarius. Image via EarthSky.

If you’re outside on an August or September evening, you can glimpse the zodiacal constellation Sagittarius the Archer. From our northerly latitudes, it never climbs high in the sky. Yet when you’re looking toward Sagittarius, you’re looking in the direction of one of the most wondrous places we can imagine: the center of our own Milky Way galaxy.

Plus, Sagittarius is fairly easy to spot if you have a dark sky. Its brightest stars form an asterism in the distinctive shape of a Teapot.

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How to find Sagittarius

You’ll want a dark, rural location to see and enjoy Sagittarius. In August or September, when you’re outside camping or ending a picnic on a summer evening – any place away from light pollution – simply look up. You’ll notice the starlit band of the Milky Way. It’ll appear as a hazy band stretching all the way across the sky. The haze is really countless stars.

From the Northern Hemisphere, the starlit trail of the Milky Way seems to bulge just before it reaches the southern horizon (from the Southern Hemipshere, this bulge is high in the sky). This bulge marks the approximate location of the Milky Way’s center.

Here’s another way to find Sagittarius. If you’re familiar with the Summer Triangle asterism, draw an imaginary line from the star Deneb and through the star Altair to locate Sagittarius near the horizon. At mid-northern latitudes, the Summer Triangle hangs high in the south to overhead on late summer and autumn evenings.

Deep-sky wonders in the Archer

So Sagittarius points to the heart of our Milky Way galaxy. But we can’t see all the way to the center. Why not? Because it’s so far away, 26,000 light-years. And because of the huge plethora of stars, star clusters, nebulae and dust that block our view.

On the other hand, the stars, star clusters, nebulae and dust are themselves worth viewing! And you don’t need to know what you’re seeing to enjoy them. Just take binoculars with you, next time you know you’ll have access to a dark sky on an August or September evening. Look up! And aim your binoculars along the starry path of the Milky Way.

Here are some deep-sky treasures in Sagittarius: Sagittarius Star Cloud (Messier 24), globular cluster Messier 22, Lagoon Nebula (Messier 8), Trifid Nebula (Messier 20) and Omega Nebula (Messier 17).

Sharp-eyed people can even see these deep-sky objects with the unaided eye. Binoculars let you see them better. And a small telescope would give you a beautiful view.

Modern stargazers have difficulty making out the Centaur in Sagittarius. But the Teapot is easy to see, once you learn to look for it. Find the Teapot, and it’ll help you on your star-hopping adventures to deep-sky marvels.

View at EarthSky Community Photos. | Miguel Sala at the Ruins of Ares Castle in Teruel, Spain, captured this photo of the Milky Way on July 10, 2021. Notice near the center of the photo that he has marked the direction of the star-rich center of our galaxy. When we look in this direction, we’re looking toward a sky crowded with star clusters and nebulae. The famous Teapot in Sagittarius – a visual guide to the galaxy’s center – is also in this direction (and on the left side of this photo). Thank you, Miguel!

Photos of the Teapot

The Teapot is the central region of Sagittarius. Once you’ve learned to trace the Teapot’s shape in the sky, it’ll become easier to spot. Check out the photos below to learn its shape and then try to spot it yourself.

View at EarthSky Community Photos. | Catherine Hyde in Cambria, California, captured this photo of the Milky Way on July 10, 2023. Catherine wrote: “This is the Teapot asterism rising from behind a tree. I’ve heard if you can capture the galactic center (Milky Way) behind it, it looks like steam coming out of the spout. I was surprised by how many deep-sky objects I had captured, so I annotated the image.” Thank you, Catherine!

View at EarthSky Community Photos. | Kannan A in Singapore took this photo on May 20, 2021. Kannan wrote: “Sagittarius may look like a teapot, but he is in fact an archer – and a four-legged one to boot: a centaur, to be specific – half horse, half man. The front of the teapot is the bow he pulls back, the spout is the tip of his arrow he aims westward at Scorpius. The remainder of the teapot are stars marking the centaur’s upper body and pulled-back arm; fainter stars southeastward sketch out his lower horsey half.” Thank you, Kannan!

The stars of Sagittarius

The brightest star in Sagittarius is the star marking the bottom right corner of the teapot, Kaus Australis. Also known as Epsilon Sagittarii, this magnitude 1.8 star lies 143 light-years away.

The next brightest star is at the opposite end of the teapot, the top star in the handle, Nunki. Also known as Sigma Sagittarii, this 2.1-magnitude star shines from a distance of 228 light-years.

Most of the other stars in Sagittarius are of 2nd and 3rd magnitude. The star marking the top of the teapot’s lid is Kaus Borealis, a magnitude 2.82 star lying 77 light-years away. The stars marking the top of the spout are Alnasl, which marks the tip of the spout at magnitude 2.98 and is 96 light-years away, and Kaus Media, which marks the spout’s connection to the pot at magnitude 2.72 and is 306 light-years away. The star at the bottom of the handle where it connects to the pot is Ascella, a magnitude 2.60 star lying 89 light-years away.

The constellation Sagittarius, with the Teapot asterism outlined in green. Chart via IAU/ Wikipedia.

Sagittarius in mythology

The constellations Sagittarius and Centaurus are both supposed to represent a centaur, a creature with the upper torso of a man and the body and legs of a horse. Historically, centaurs might have really been like cowboys, using horses to round up cattle in ancient Greece.

According to Greek myth, the centaurs were the offspring of Ixion and the cloud nymph Nephele. Apparently, Sagittarius’ drawn-out bow and arrow originated from the Mesopotamian archer god. So this constellation might not have always represented the centaur Chiron.

It’s said that the Greeks associated Sagittarius with Crotus the satyr, another type of monstrosity, a man with horse ears and tail and goat legs. Quite possibly, the Romans first identified the constellation Sagittarius with Chiron, the wise and kindly centaur.

Here’s something that distinguishes Sagittarius the Archer from the other 13 constellations of the zodiac. The sun shines in front of this constellation on the December 21 solstice.

Also, the ecliptic – the sun’s yearly pathway in front of the backdrop stars – intersects the galactic equator in Sagittarius.

Sagittarius as depicted in Urania’s Mirror, a set of constellation cards published in London in 1825. Image via Wikimedia.

The constellation versus the sign

In our modern times, the sun passes in front of the constellation Sagittarius from about December 18 to January 20. These dates are off by about a month from what you read on the horoscope page. The sun moves through the sign Sagittarius from about November 21 to December 21.

Yes, there is a difference between an astronomical constellation and an astrological sign! Keep in mind that we’re talking about the constellation Sagittarius in this article. The horoscope is referring to the sign Sagittarius.

By definition, the sun enters the sign Sagittarius whenever the sun is precisely 30 degrees west of the December solstice point. Then, on the December solstice, the sun enters the sign Capricorn.

While the signs remain fixed relative to the solstices and equinoxes, the solstices and equinox points move 30 degrees westward in front of the constellations – or backdrop stars – in about 2,160 years.

The constellation boundaries were formally defined by the International Astronomical Union (IAU) in 1930. Based on the present IAU boundaries, the December solstice point moved into the constellation Sagittarius in the year 131 BCE and will move into the constellation Ophiuchus in 2269 CE.

Bottom line: Look for the constellation Sagittarius on an August or September evening. The brightest stars in Sagittarius form the distinctive shape of a teapot. And the spout of the Teapot points to the center of the Milky Way galaxy.

Teapot of Sagittarius points to the Milky Way’s center

The post Sagittarius the Archer is home to deep-sky wonders first appeared on EarthSky.

from EarthSky https://ift.tt/BMQgPym

Sagittarius the Archer contains a Teapot shape. It’s located in the direction of the center of our Milky Way galaxy. If you live far enough south – say at least at latitudes like those in the southern U.S., or farther south – you might spot the arcing shape of Corona Australis near Sagittarius. Image via EarthSky.

If you’re outside on an August or September evening, you can glimpse the zodiacal constellation Sagittarius the Archer. From our northerly latitudes, it never climbs high in the sky. Yet when you’re looking toward Sagittarius, you’re looking in the direction of one of the most wondrous places we can imagine: the center of our own Milky Way galaxy.

Plus, Sagittarius is fairly easy to spot if you have a dark sky. Its brightest stars form an asterism in the distinctive shape of a Teapot.

Catch the wonder of the night sky. Subscribe to EarthSky’s free daily newsletter for the latest in science, stars, planets and more.

How to find Sagittarius

You’ll want a dark, rural location to see and enjoy Sagittarius. In August or September, when you’re outside camping or ending a picnic on a summer evening – any place away from light pollution – simply look up. You’ll notice the starlit band of the Milky Way. It’ll appear as a hazy band stretching all the way across the sky. The haze is really countless stars.

From the Northern Hemisphere, the starlit trail of the Milky Way seems to bulge just before it reaches the southern horizon (from the Southern Hemipshere, this bulge is high in the sky). This bulge marks the approximate location of the Milky Way’s center.

Here’s another way to find Sagittarius. If you’re familiar with the Summer Triangle asterism, draw an imaginary line from the star Deneb and through the star Altair to locate Sagittarius near the horizon. At mid-northern latitudes, the Summer Triangle hangs high in the south to overhead on late summer and autumn evenings.

Deep-sky wonders in the Archer

So Sagittarius points to the heart of our Milky Way galaxy. But we can’t see all the way to the center. Why not? Because it’s so far away, 26,000 light-years. And because of the huge plethora of stars, star clusters, nebulae and dust that block our view.

On the other hand, the stars, star clusters, nebulae and dust are themselves worth viewing! And you don’t need to know what you’re seeing to enjoy them. Just take binoculars with you, next time you know you’ll have access to a dark sky on an August or September evening. Look up! And aim your binoculars along the starry path of the Milky Way.

Here are some deep-sky treasures in Sagittarius: Sagittarius Star Cloud (Messier 24), globular cluster Messier 22, Lagoon Nebula (Messier 8), Trifid Nebula (Messier 20) and Omega Nebula (Messier 17).

Sharp-eyed people can even see these deep-sky objects with the unaided eye. Binoculars let you see them better. And a small telescope would give you a beautiful view.

Modern stargazers have difficulty making out the Centaur in Sagittarius. But the Teapot is easy to see, once you learn to look for it. Find the Teapot, and it’ll help you on your star-hopping adventures to deep-sky marvels.

View at EarthSky Community Photos. | Miguel Sala at the Ruins of Ares Castle in Teruel, Spain, captured this photo of the Milky Way on July 10, 2021. Notice near the center of the photo that he has marked the direction of the star-rich center of our galaxy. When we look in this direction, we’re looking toward a sky crowded with star clusters and nebulae. The famous Teapot in Sagittarius – a visual guide to the galaxy’s center – is also in this direction (and on the left side of this photo). Thank you, Miguel!

Photos of the Teapot

The Teapot is the central region of Sagittarius. Once you’ve learned to trace the Teapot’s shape in the sky, it’ll become easier to spot. Check out the photos below to learn its shape and then try to spot it yourself.

View at EarthSky Community Photos. | Catherine Hyde in Cambria, California, captured this photo of the Milky Way on July 10, 2023. Catherine wrote: “This is the Teapot asterism rising from behind a tree. I’ve heard if you can capture the galactic center (Milky Way) behind it, it looks like steam coming out of the spout. I was surprised by how many deep-sky objects I had captured, so I annotated the image.” Thank you, Catherine!

View at EarthSky Community Photos. | Kannan A in Singapore took this photo on May 20, 2021. Kannan wrote: “Sagittarius may look like a teapot, but he is in fact an archer – and a four-legged one to boot: a centaur, to be specific – half horse, half man. The front of the teapot is the bow he pulls back, the spout is the tip of his arrow he aims westward at Scorpius. The remainder of the teapot are stars marking the centaur’s upper body and pulled-back arm; fainter stars southeastward sketch out his lower horsey half.” Thank you, Kannan!

The stars of Sagittarius

The brightest star in Sagittarius is the star marking the bottom right corner of the teapot, Kaus Australis. Also known as Epsilon Sagittarii, this magnitude 1.8 star lies 143 light-years away.

The next brightest star is at the opposite end of the teapot, the top star in the handle, Nunki. Also known as Sigma Sagittarii, this 2.1-magnitude star shines from a distance of 228 light-years.

Most of the other stars in Sagittarius are of 2nd and 3rd magnitude. The star marking the top of the teapot’s lid is Kaus Borealis, a magnitude 2.82 star lying 77 light-years away. The stars marking the top of the spout are Alnasl, which marks the tip of the spout at magnitude 2.98 and is 96 light-years away, and Kaus Media, which marks the spout’s connection to the pot at magnitude 2.72 and is 306 light-years away. The star at the bottom of the handle where it connects to the pot is Ascella, a magnitude 2.60 star lying 89 light-years away.

The constellation Sagittarius, with the Teapot asterism outlined in green. Chart via IAU/ Wikipedia.

Sagittarius in mythology

The constellations Sagittarius and Centaurus are both supposed to represent a centaur, a creature with the upper torso of a man and the body and legs of a horse. Historically, centaurs might have really been like cowboys, using horses to round up cattle in ancient Greece.

According to Greek myth, the centaurs were the offspring of Ixion and the cloud nymph Nephele. Apparently, Sagittarius’ drawn-out bow and arrow originated from the Mesopotamian archer god. So this constellation might not have always represented the centaur Chiron.

It’s said that the Greeks associated Sagittarius with Crotus the satyr, another type of monstrosity, a man with horse ears and tail and goat legs. Quite possibly, the Romans first identified the constellation Sagittarius with Chiron, the wise and kindly centaur.

Here’s something that distinguishes Sagittarius the Archer from the other 13 constellations of the zodiac. The sun shines in front of this constellation on the December 21 solstice.

Also, the ecliptic – the sun’s yearly pathway in front of the backdrop stars – intersects the galactic equator in Sagittarius.

Sagittarius as depicted in Urania’s Mirror, a set of constellation cards published in London in 1825. Image via Wikimedia.

The constellation versus the sign

In our modern times, the sun passes in front of the constellation Sagittarius from about December 18 to January 20. These dates are off by about a month from what you read on the horoscope page. The sun moves through the sign Sagittarius from about November 21 to December 21.

Yes, there is a difference between an astronomical constellation and an astrological sign! Keep in mind that we’re talking about the constellation Sagittarius in this article. The horoscope is referring to the sign Sagittarius.

By definition, the sun enters the sign Sagittarius whenever the sun is precisely 30 degrees west of the December solstice point. Then, on the December solstice, the sun enters the sign Capricorn.

While the signs remain fixed relative to the solstices and equinoxes, the solstices and equinox points move 30 degrees westward in front of the constellations – or backdrop stars – in about 2,160 years.

The constellation boundaries were formally defined by the International Astronomical Union (IAU) in 1930. Based on the present IAU boundaries, the December solstice point moved into the constellation Sagittarius in the year 131 BCE and will move into the constellation Ophiuchus in 2269 CE.

Bottom line: Look for the constellation Sagittarius on an August or September evening. The brightest stars in Sagittarius form the distinctive shape of a teapot. And the spout of the Teapot points to the center of the Milky Way galaxy.

Teapot of Sagittarius points to the Milky Way’s center

The post Sagittarius the Archer is home to deep-sky wonders first appeared on EarthSky.

from EarthSky https://ift.tt/BMQgPym