Hydrothermal activity on Mars? Rover finds tantalizing new clues

View larger. | NASA’s Mars Reconnaissance Orbiter (MRO) spacecraft took this image of part of Jezero crater from orbit. The enhanced colors highlight various mineral deposits. Here, you can clearly see the large delta, where river water once emptied into the crater lake billions of years ago. It is in this region that NASA’s Perseverance rover found the silica-rich rocks, including – for the 1st time – quartz. The findings suggest hydrothermal activity on Mars billions of years ago. Image via NASA/ JPL-Caltech/ MSSS/ JHU-APL.

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• Hydrothermal systems – hot underground water – are common on Earth. Did they also once exist on Mars?
• NASA’s Perseverance rover has found silica-rich rocks in Jezero crater. This includes the first confirmed discovery of quartz. The various silica deposits are evidence of ancient hydrothermal activity on Mars.
• On Earth, hydrothermal systems provide habitats for many different kinds of microbes. Silica-rich rocks are also ideal for preserving traces of ancient microbial organisms.

Hydrothermal activity on Mars?

NASA’s Perseverance rover has been in the news a lot recently, with findings that hint at possible ancient microbial life on Mars. And now, the intrepid rover has made yet another intriguing discovery. On April 2, 2025, an international team of researchers said that Perseverance has found evidence for previous hydrothermal – hot water – activity where it landed in Jezero crater. The rover detected crystallized quartz and hydrated silica in rocks it analyzed, suggesting heated water and potential habitability for microbes.

The researchers, from Grenoble Alpes University, CNRS, Sorbonne Université and other French institutions, published their peer-reviewed results in Earth and Planetary Science Letters on February 28, 2025. The paper is also included in volume 656 of the journal (April 15, 2025).

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!

Silica-rich rocks

Perseverance found rocks containing opaline silica (opal), chalcedony and quartz at three locations. They are at the edge of the ancient delta inside Jezero crater, along the riverbed that connects to the delta and on the edge of the crater rim. The rover used its SuperCam instrument to identify the silica minerals. This involved a combination of laser-induced breakdown spectroscopy (LIBS), infrared (IR) and Raman spectroscopy.

Overall, the researchers studied six samples that Perseverance obtained and analyzed.

Quartz and silica point to past hydrothermal activity on Mars

The researchers found high amounts of silicon, and some rocks were nearly pure silica. In addition, they also identified hydrated silica, opaline silica, chalcedony and well-crystallized quartz. In particular, the quartz is of special interest, since this is the first time that scientists have definitively identified it on Mars. Notably, this is the first time that quartz-dominated rocks have been confirmed on Mars.

Together, the deposits point to a likely hydrothermal origin for the minerals. The paper states:

Quartz-dominated stones are detected unambiguously for the first time on the Martian surface, and based on grain size and crystallinity are proposed to be of hydrothermal origin. Although these rocks were all found as float, we propose that these detections are part of a common hydrothermal system, and represent different depths/temperatures of precipitation. This attests that hydrothermal processes were active in and around Jezero crater, possibly triggered by the Jezero crater-forming impact.

View larger. | Locations of the 3 high-silica rock targets within and on the edge of Jezero crater. The red star is opal, the green star is chalcedony and the black star is quartz. Image via P. Beck et al/ Earth and Planetary Science Letters (CC BY).

Pierre Beck at Grenoble Alpes University in France is the lead author of the new silica study. Image via University Institute of France.

Implications for possible past life

So, why is hydrothermal activity significant? Hydrothermal systems – heated underground water – are common on Earth. Although the water is super hot, it provides habitable conditions for a wide variety of microscopic life. Could the same have been true on Mars?

Also, such silica-rich rocks are ideal for preserving traces of once-living microbes. Opaline silica is known for its ability to preserve both molecular and macroscopic biosignatures. Biosignatures are molecular, chemical or other traces of life. As the paper notes:

These silica-rich rocks, in particular opaline silica, are very promising targets for sampling and return to Earth given their high biosignature preservation potential.

Interestingly, NASA’s Spirit rover also found opaline silica back in 2008. But what made this silica even more interesting was its shape. Its outer layers were covered in tiny nodules that looked like heads of cauliflower. In fact, the cauliflower formations closely resembled ones on Earth, in the Atacama Desert in Chile, Yellowstone National Park in Wyoming and the Taupo Volcanic Zone in New Zealand, where microbial life was involved in their creation.

View larger. | NASA’s Spirit rover also saw these cauliflower-shaped silica formations back in 2008. In fact, they closely resemble ones on Earth, in the Atacama Desert in Chile, Yellowstone National Park in Wyoming and the Taupo Volcanic Zone in New Zealand, where microbial life was involved in their creation. Image via NASA/ JPL-Caltech/ Smithsonian.

On the lookout for more silica rocks

Unfortunately, the rocks were too small for the rover to drill into and obtain samples that it could further analyze in its onboard mini-laboratory or store away for eventual return to Earth for the Mars Sample Return program. The rover team is eager to find more, however, as Perseverance continues exploring. For astrobiology research, the opaline silica and hydrated silica are of special interest, as the paper says:

Thus, the presence of opaline silica could be related to the presence of organic compounds, making it a promising target to explore the organic chemistry that once existed on early Mars. While the rock described in this work was too small for drilling and collection, the Perseverance rover team will be looking for similar targets in the coming years.

The discovery of hydrated silica is promising for the search for organic traces of life on Mars, since a hydrated silica matrix reduces the molecular degradation of fossil microorganisms over time, as demonstrated experimentally.

Indeed, the findings provide compelling evidence for not only hydrothermal activity on ancient Mars, but even potential habitability. It will be interesting to what else Perseverance – and its companion rover Curiosity – discovers, to be sure.

Bottom line: NASA’s Perseverance rover has found silica-rich rocks, including – for the first time – quartz. It’s compelling evidence of ancient hydrothermal activity on Mars.

Source: From hydrated silica to quartz: Potential hydrothermal precipitates found in Jezero crater, Mars

Via Spectroscopy

Read more: Life on Mars? Odd rings and spots tantalize scientists

Read more: Green spots in rocks on Mars intrigue rover scientists

The post Hydrothermal activity on Mars? Rover finds tantalizing new clues first appeared on EarthSky.

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View larger. | NASA’s Mars Reconnaissance Orbiter (MRO) spacecraft took this image of part of Jezero crater from orbit. The enhanced colors highlight various mineral deposits. Here, you can clearly see the large delta, where river water once emptied into the crater lake billions of years ago. It is in this region that NASA’s Perseverance rover found the silica-rich rocks, including – for the 1st time – quartz. The findings suggest hydrothermal activity on Mars billions of years ago. Image via NASA/ JPL-Caltech/ MSSS/ JHU-APL.

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Join our 2025 Donation Campaign today.

• Hydrothermal systems – hot underground water – are common on Earth. Did they also once exist on Mars?
• NASA’s Perseverance rover has found silica-rich rocks in Jezero crater. This includes the first confirmed discovery of quartz. The various silica deposits are evidence of ancient hydrothermal activity on Mars.
• On Earth, hydrothermal systems provide habitats for many different kinds of microbes. Silica-rich rocks are also ideal for preserving traces of ancient microbial organisms.

Hydrothermal activity on Mars?

NASA’s Perseverance rover has been in the news a lot recently, with findings that hint at possible ancient microbial life on Mars. And now, the intrepid rover has made yet another intriguing discovery. On April 2, 2025, an international team of researchers said that Perseverance has found evidence for previous hydrothermal – hot water – activity where it landed in Jezero crater. The rover detected crystallized quartz and hydrated silica in rocks it analyzed, suggesting heated water and potential habitability for microbes.

The researchers, from Grenoble Alpes University, CNRS, Sorbonne Université and other French institutions, published their peer-reviewed results in Earth and Planetary Science Letters on February 28, 2025. The paper is also included in volume 656 of the journal (April 15, 2025).

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!

Silica-rich rocks

Perseverance found rocks containing opaline silica (opal), chalcedony and quartz at three locations. They are at the edge of the ancient delta inside Jezero crater, along the riverbed that connects to the delta and on the edge of the crater rim. The rover used its SuperCam instrument to identify the silica minerals. This involved a combination of laser-induced breakdown spectroscopy (LIBS), infrared (IR) and Raman spectroscopy.

Overall, the researchers studied six samples that Perseverance obtained and analyzed.

Quartz and silica point to past hydrothermal activity on Mars

The researchers found high amounts of silicon, and some rocks were nearly pure silica. In addition, they also identified hydrated silica, opaline silica, chalcedony and well-crystallized quartz. In particular, the quartz is of special interest, since this is the first time that scientists have definitively identified it on Mars. Notably, this is the first time that quartz-dominated rocks have been confirmed on Mars.

Together, the deposits point to a likely hydrothermal origin for the minerals. The paper states:

Quartz-dominated stones are detected unambiguously for the first time on the Martian surface, and based on grain size and crystallinity are proposed to be of hydrothermal origin. Although these rocks were all found as float, we propose that these detections are part of a common hydrothermal system, and represent different depths/temperatures of precipitation. This attests that hydrothermal processes were active in and around Jezero crater, possibly triggered by the Jezero crater-forming impact.

View larger. | Locations of the 3 high-silica rock targets within and on the edge of Jezero crater. The red star is opal, the green star is chalcedony and the black star is quartz. Image via P. Beck et al/ Earth and Planetary Science Letters (CC BY).

Pierre Beck at Grenoble Alpes University in France is the lead author of the new silica study. Image via University Institute of France.

Implications for possible past life

So, why is hydrothermal activity significant? Hydrothermal systems – heated underground water – are common on Earth. Although the water is super hot, it provides habitable conditions for a wide variety of microscopic life. Could the same have been true on Mars?

Also, such silica-rich rocks are ideal for preserving traces of once-living microbes. Opaline silica is known for its ability to preserve both molecular and macroscopic biosignatures. Biosignatures are molecular, chemical or other traces of life. As the paper notes:

These silica-rich rocks, in particular opaline silica, are very promising targets for sampling and return to Earth given their high biosignature preservation potential.

Interestingly, NASA’s Spirit rover also found opaline silica back in 2008. But what made this silica even more interesting was its shape. Its outer layers were covered in tiny nodules that looked like heads of cauliflower. In fact, the cauliflower formations closely resembled ones on Earth, in the Atacama Desert in Chile, Yellowstone National Park in Wyoming and the Taupo Volcanic Zone in New Zealand, where microbial life was involved in their creation.

View larger. | NASA’s Spirit rover also saw these cauliflower-shaped silica formations back in 2008. In fact, they closely resemble ones on Earth, in the Atacama Desert in Chile, Yellowstone National Park in Wyoming and the Taupo Volcanic Zone in New Zealand, where microbial life was involved in their creation. Image via NASA/ JPL-Caltech/ Smithsonian.

On the lookout for more silica rocks

Unfortunately, the rocks were too small for the rover to drill into and obtain samples that it could further analyze in its onboard mini-laboratory or store away for eventual return to Earth for the Mars Sample Return program. The rover team is eager to find more, however, as Perseverance continues exploring. For astrobiology research, the opaline silica and hydrated silica are of special interest, as the paper says:

Thus, the presence of opaline silica could be related to the presence of organic compounds, making it a promising target to explore the organic chemistry that once existed on early Mars. While the rock described in this work was too small for drilling and collection, the Perseverance rover team will be looking for similar targets in the coming years.

The discovery of hydrated silica is promising for the search for organic traces of life on Mars, since a hydrated silica matrix reduces the molecular degradation of fossil microorganisms over time, as demonstrated experimentally.

Indeed, the findings provide compelling evidence for not only hydrothermal activity on ancient Mars, but even potential habitability. It will be interesting to what else Perseverance – and its companion rover Curiosity – discovers, to be sure.

Bottom line: NASA’s Perseverance rover has found silica-rich rocks, including – for the first time – quartz. It’s compelling evidence of ancient hydrothermal activity on Mars.

Source: From hydrated silica to quartz: Potential hydrothermal precipitates found in Jezero crater, Mars

Via Spectroscopy

Read more: Life on Mars? Odd rings and spots tantalize scientists

Read more: Green spots in rocks on Mars intrigue rover scientists

The post Hydrothermal activity on Mars? Rover finds tantalizing new clues first appeared on EarthSky.

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Hubble reveals weird Uranus in new 20-year study

View larger. | Various observations of Uranus by the Hubble Space Telescope over the 20-year period from 2002 to 2022. The findings yield new insights into Uranus’ atmosphere and how it might compare to exoplanets similar to Uranus. Image via NASA/ ESA/ Erich Karkoschka (LPL)/ Hubblesite.

• Uranus is an ice giant planet in the outer solar system, similar to Neptune. It has a deep atmosphere of hydrogen, helium and methane.
• NASA’s Hubble Space Telescope observed Uranus over 20 years for a detailed study. The observations provided new insights into the mysterious planet’s atmosphere.
• Hubble studied the distribution of methane and aerosol clouds over time, which varied depending on the seasons and the latitudes of the methane and clouds.

Hubble reveals weird Uranus in new 20-year study

NASA’s Hubble Space Telescope observed the distant ice giant planet Uranus repeatedly over the course of 20 years. The Space Telescope Science Institute (STScI) said on March 31, 2025, that the two-decade long study has yielded new insights into the dynamics of its deep hydrogen, helium and methane atmosphere. The findings can also help astronomers better understand exoplanets that are similar in size and composition to Uranus.

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!

20 years of Uranus observations

Hubble observed Uranus four times during the 20-year period, in 2002, 2012, 2015 and 2022. Erich Karkoschka at the University of Arizona and Larry Sromovsky and Pat Fry at the University of Wisconsin led the research team. They used the Space Telescope Imaging Spectrograph (STIS) instrument on Hubble to chronicle seasonal changes in Uranus’ bluish-green atmosphere.

Why did it take so long? Uranus has the most extreme seasons of any planet in the solar system. This is due to its axial tilt of a whopping 98 degrees. Each of its four seasons lasts 21 years, and a year on Uranus is just over 84 Earth years!

Uranus’ atmosphere is much deeper than Earth’s and consists mostly of hydrogen and helium, plus some methane. There are also trace amounts of water and ammonia.

The 20-year study revealed that methane is not evenly distributed through Uranus’ atmosphere. This is different than what happens on the gas giant planets Jupiter and Saturn. Notably, on Uranus, the methane is strongly depleted near the planet’s poles. The depletion remained pretty much unchanged over the 20 years. Interestingly, however, aerosols and hazes did change. They brightened in the north polar region. This is happening as the planet starts to approach its northern summer solstice in 2030.

View larger. | NASA’s James Webb Space Telescope captured this stunning view of Uranus and its rings on February 6, 2023. Image via NASA/ ESA/ CSA/ STScI/ J. DePasquale (STScI).

Analyzing the images

The composite of 16 images included above shows the observations of Uranus’ atmosphere in both visible and near-infrared light. It also shows the aerosols, hazes and methane depletion in the atmosphere. Over the 20 years, the south polar region started going into the shadow of winter. Conversely, the north polar region came into sunlight as summer approached.

In the top row, we see Uranus as it looks to the human eye, in visible light. It’s bland, with only subtle variations. The second row shows Uranus in false color, from both visible light and near-infrared light observations. The colors depict varying amounts of methane and aerosols in the atmosphere. Green areas generally indicate less methane than blue areas, and red areas are where there is no methane.

The third row shows bright areas on Uranus, with more aerosol clouds and haze in the atmosphere. By contrast, the darker areas have less clouds. Finally, the fourth row focuses on methane. Bright areas have less methane and dark areas have more methane.

Both the third and fourth row images are based on 1,000 different wavelengths (colors), ranging from visible to near infrared light.

The aerosols and methane behave differently at different latitudes. Neither of them showed much change over the 20 years at middle and low latitudes. But near the north pole, the aerosols significantly increased. The methane depletion, however, remained high at both poles.

Astronomers can also now use the findings to help better understand exoplanets that are similar in size and composition to Uranus.

Erich Karkoschka at the University of Arizona is one of the lead researchers of the Uranus study. Image via Lunar and Planetary Laboratory.

Uranus is weird

The first – and still only – spacecraft to visit Uranus was Voyager 2 on January 24, 1986. It saw Uranus up close for the first time ever. While Uranus’ atmosphere was a lovely bluish-green, it was also bland, not like the turbulent, striped atmospheres of Jupiter and Saturn. But one of the weirdest things about Uranus is that it rotates sideways. Its axis is extremely tipped, at about 98 degrees. By comparison, Earth’s axis only tips 23.45 degrees.

Another study in late 2024 also suggested that both Uranus and Neptune might have deep oceans of water beneath their atmospheres. This could also explain why both planets have unusually disorganized magnetic fields.

Bottom line: The Hubble Space Telescope’s 20-year study of Uranus has yielded new insights about the enigmatic ice giant’s atmosphere and how it might compare to exoplanets.

Via Hubblesite

Read more: Are Uranus and Neptune hiding oceans of water?

Read more: New Uranus image from Webb shows rings, polar cap

The post Hubble reveals weird Uranus in new 20-year study first appeared on EarthSky.

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View larger. | Various observations of Uranus by the Hubble Space Telescope over the 20-year period from 2002 to 2022. The findings yield new insights into Uranus’ atmosphere and how it might compare to exoplanets similar to Uranus. Image via NASA/ ESA/ Erich Karkoschka (LPL)/ Hubblesite.

• Uranus is an ice giant planet in the outer solar system, similar to Neptune. It has a deep atmosphere of hydrogen, helium and methane.
• NASA’s Hubble Space Telescope observed Uranus over 20 years for a detailed study. The observations provided new insights into the mysterious planet’s atmosphere.
• Hubble studied the distribution of methane and aerosol clouds over time, which varied depending on the seasons and the latitudes of the methane and clouds.

Hubble reveals weird Uranus in new 20-year study

NASA’s Hubble Space Telescope observed the distant ice giant planet Uranus repeatedly over the course of 20 years. The Space Telescope Science Institute (STScI) said on March 31, 2025, that the two-decade long study has yielded new insights into the dynamics of its deep hydrogen, helium and methane atmosphere. The findings can also help astronomers better understand exoplanets that are similar in size and composition to Uranus.

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!

20 years of Uranus observations

Hubble observed Uranus four times during the 20-year period, in 2002, 2012, 2015 and 2022. Erich Karkoschka at the University of Arizona and Larry Sromovsky and Pat Fry at the University of Wisconsin led the research team. They used the Space Telescope Imaging Spectrograph (STIS) instrument on Hubble to chronicle seasonal changes in Uranus’ bluish-green atmosphere.

Why did it take so long? Uranus has the most extreme seasons of any planet in the solar system. This is due to its axial tilt of a whopping 98 degrees. Each of its four seasons lasts 21 years, and a year on Uranus is just over 84 Earth years!

Uranus’ atmosphere is much deeper than Earth’s and consists mostly of hydrogen and helium, plus some methane. There are also trace amounts of water and ammonia.

The 20-year study revealed that methane is not evenly distributed through Uranus’ atmosphere. This is different than what happens on the gas giant planets Jupiter and Saturn. Notably, on Uranus, the methane is strongly depleted near the planet’s poles. The depletion remained pretty much unchanged over the 20 years. Interestingly, however, aerosols and hazes did change. They brightened in the north polar region. This is happening as the planet starts to approach its northern summer solstice in 2030.

View larger. | NASA’s James Webb Space Telescope captured this stunning view of Uranus and its rings on February 6, 2023. Image via NASA/ ESA/ CSA/ STScI/ J. DePasquale (STScI).

Analyzing the images

The composite of 16 images included above shows the observations of Uranus’ atmosphere in both visible and near-infrared light. It also shows the aerosols, hazes and methane depletion in the atmosphere. Over the 20 years, the south polar region started going into the shadow of winter. Conversely, the north polar region came into sunlight as summer approached.

In the top row, we see Uranus as it looks to the human eye, in visible light. It’s bland, with only subtle variations. The second row shows Uranus in false color, from both visible light and near-infrared light observations. The colors depict varying amounts of methane and aerosols in the atmosphere. Green areas generally indicate less methane than blue areas, and red areas are where there is no methane.

The third row shows bright areas on Uranus, with more aerosol clouds and haze in the atmosphere. By contrast, the darker areas have less clouds. Finally, the fourth row focuses on methane. Bright areas have less methane and dark areas have more methane.

Both the third and fourth row images are based on 1,000 different wavelengths (colors), ranging from visible to near infrared light.

The aerosols and methane behave differently at different latitudes. Neither of them showed much change over the 20 years at middle and low latitudes. But near the north pole, the aerosols significantly increased. The methane depletion, however, remained high at both poles.

Astronomers can also now use the findings to help better understand exoplanets that are similar in size and composition to Uranus.

Erich Karkoschka at the University of Arizona is one of the lead researchers of the Uranus study. Image via Lunar and Planetary Laboratory.

Uranus is weird

The first – and still only – spacecraft to visit Uranus was Voyager 2 on January 24, 1986. It saw Uranus up close for the first time ever. While Uranus’ atmosphere was a lovely bluish-green, it was also bland, not like the turbulent, striped atmospheres of Jupiter and Saturn. But one of the weirdest things about Uranus is that it rotates sideways. Its axis is extremely tipped, at about 98 degrees. By comparison, Earth’s axis only tips 23.45 degrees.

Another study in late 2024 also suggested that both Uranus and Neptune might have deep oceans of water beneath their atmospheres. This could also explain why both planets have unusually disorganized magnetic fields.

Bottom line: The Hubble Space Telescope’s 20-year study of Uranus has yielded new insights about the enigmatic ice giant’s atmosphere and how it might compare to exoplanets.

Via Hubblesite

Read more: Are Uranus and Neptune hiding oceans of water?

Read more: New Uranus image from Webb shows rings, polar cap

The post Hubble reveals weird Uranus in new 20-year study first appeared on EarthSky.

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The Coma Berenices galaxy cluster, best in April and May

View larger. | This Hubble Space Telescope mosaic is of a portion of the immense Coma Berenices galaxy cluster. Be sure to use the view larger link and zoom in to see how much larger the football-shaped elliptical galaxies are, in contrast to the spiral galaxies. Image via NASA/ ESA/ J. Mack (STScI)/ J. Madrid (Australian Telescope National Facility).

The Coma Berenices galaxy cluster

Thousands of galaxies lie in the Coma Berenices cluster. It’s one of the densest known galactic groupings visible through telescopes from Earth. It’s located in the direction of the constellation Coma Berenices. And it’s best viewed in the evening in April and May. The center of the Coma Berenices cluster is about 320 million light-years away. The cluster spans a distance of space of about 20 million light-years. That’s in contrast to our home galaxy, the Milky Way, about 100,000 light-years wide.

And the Coma Berenices cluster isn’t just one galaxy. It’s a huge collection of these star islands in space, filled with galaxies of all shapes and sizes, from giant ellipticals to spirals to dwarf galaxies.

An old – but beautiful – name for this region of sky is the Realm of the Galaxies. Writing an article by that name for Frosty Drew Observatory in the year 2000, the late Leslie Coleman, a previous director of Frosty Drew, explained:

Even in the eyepiece of the 16″, many of the galaxies in this area overlap each other! There simply isn’t room enough in this region of the sky to fit them.

It occupies a small area of sky

The central part of the Coma Berenices cluster covers a roughly circular area about 1 1/2 degrees across. That’s nine times the area of a full moon, which is about 1/2 a degree across. However, the full cluster may extend farther, and numerous other galaxy clusters are in the same area of the sky.

The constellation Coma Berenices lies between the constellations Leo the Lion and Boötes the Herdsman. This part of the sky is the site of the famous open star cluster known as the Coma Berenices star cluster, as well as the most distant galaxy cluster visible through telescopes. To see the star cluster and the galaxy cluster you need a dark sky.

How to find the Coma Berenices galaxy cluster

The galaxy cluster is near the northern border of the constellation Coma Berenices.

Here’s a chart of the constellation Coma Berenices. The blue star indicates the approximate location of the center of the Coma Berenices galaxy cluster. Image via IAU.

The cluster contains thousands of galaxies

The constellation Coma Berenices appears to the eye as a cluster of stars. But a telescope reveals a vast region of distant galaxies in this part of the sky. The chart below gives you an idea of the number of galaxies in that region of the sky.

No idea how twitter renders this image but "faint fuzzy" time! ASI533/8"SCT Alt/Az 50x5s subs looking thru to Coma Cluster of Galaxies. 300Mly away. Looking thru Galactic pole. Like shooting fish in a barrel! SkySafari labels two as IC 4040? Mag 15.4 captured! @BristolAstroSoc pic.twitter.com/pd3ssZn6lE

— Chris Lee FRAS FBIS (@cpl43uk) February 15, 2021

Science of the Coma Berenices galaxy cluster

So, the center of the Coma Berenices galaxy cluster is about 320 million light-years away. And it’s not getting any closer! In fact, the entire cluster is flying away from us at the rate of about more than 15 million mph (24 million kph)!

The Coma Berenices galaxy cluster is one of the most populated galaxy clusters known. And scientists estimate that it contains as many as 10,000 or more members. There are more individual galaxies in this cluster than there are stars visible to the unaided human eye on a clear, dark night.

This section of the Coma Berenices galaxy cluster is about 1/3 of the way from the cluster’s center. The bright spiral galaxy in the upper left is distinctly brighter and bluer than surrounding galaxies and has dusty spiral arms that appear reddish brown against the whiter disk of the galaxy. These are all clues that this galaxy underwent a disturbance at some point in the past. Image via Wikimedia.

A myriad of galaxies

Most galaxies in the central part of the cluster are elliptical. Elliptical galaxies are the result of galaxy mergers. The two brightest members are NGC 4889 and NGC 4874, both of which are giant ellipticals. They are at least two to three times larger than our own Milky Way galaxy. Farther out from the center are several spiral galaxies.

But most galaxies in the Coma Berenices galaxy cluster are dwarf galaxies. Maybe they resemble the Milky Way’s companions, the Large and Small Magellanic Clouds.

Closeup on the majestic face-on spiral galaxy NGC 4911 located deep within the Coma Berenices galaxy cluster. Image via NASA.

Coma Berenices galaxy cluster in history

Too faint for viewing by the human eye (or binoculars and even small telescopes), the ancients could not have seen the galaxy cluster. Hence, it has no associated mythology. However, the Coma Berenices galaxy cluster still has an interesting history.

Not only it is one of the largest and most densely populated clusters of galaxies known, it also led to our discovery of dark matter in our universe. Unseen and mysterious, this matter greatly increases the total mass and gravitational strength of the universe, affecting its evolution and fate.

Dark matter was unknown and unsuspected until Swiss-American astronomer Fritz Zwicky discovered it in the Coma Berenices galaxy cluster in the 1930s. Zwicky tallied up the visible galaxies in the cluster and estimated their masses. Then he observed the motions of galaxies near the edge of the cluster, which are determined by the total gravity (and hence mass) of the cluster. Zwicky found that the mass derived from the latter method greatly exceeded that from visual inspection.

Zwicky knew that if the law of gravity is correct – and there is no reason to doubt it – the only answer could be an additional source of mass, which he called dunkle Materie in German.

Today, scientists see the imprint of dark matter throughout the universe. It’s at least five times more prevalent than the more familiar visible matter, such as the stars and galaxies we can see.

Astronomer Fritz Zwicky 1st predicted the existence of dark matter in the 1930s, following his observations of the Coma Berenices galaxy cluster. Image via Wikimedia Commons.

Coordinates of the Coma Berenices galaxy cluster

The center of the Coma Berenices galaxy cluster is located at approximately RA: 12h 59m, dec: +27° 59′.

Bottom line: Myriads of galaxies, visible only to those with telescopes, shine among the stars of the constellation Coma Berenices. This is the distant Coma Berenices galaxy cluster.

The post The Coma Berenices galaxy cluster, best in April and May first appeared on EarthSky.

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View larger. | This Hubble Space Telescope mosaic is of a portion of the immense Coma Berenices galaxy cluster. Be sure to use the view larger link and zoom in to see how much larger the football-shaped elliptical galaxies are, in contrast to the spiral galaxies. Image via NASA/ ESA/ J. Mack (STScI)/ J. Madrid (Australian Telescope National Facility).

The Coma Berenices galaxy cluster

Thousands of galaxies lie in the Coma Berenices cluster. It’s one of the densest known galactic groupings visible through telescopes from Earth. It’s located in the direction of the constellation Coma Berenices. And it’s best viewed in the evening in April and May. The center of the Coma Berenices cluster is about 320 million light-years away. The cluster spans a distance of space of about 20 million light-years. That’s in contrast to our home galaxy, the Milky Way, about 100,000 light-years wide.

And the Coma Berenices cluster isn’t just one galaxy. It’s a huge collection of these star islands in space, filled with galaxies of all shapes and sizes, from giant ellipticals to spirals to dwarf galaxies.

An old – but beautiful – name for this region of sky is the Realm of the Galaxies. Writing an article by that name for Frosty Drew Observatory in the year 2000, the late Leslie Coleman, a previous director of Frosty Drew, explained:

Even in the eyepiece of the 16″, many of the galaxies in this area overlap each other! There simply isn’t room enough in this region of the sky to fit them.

It occupies a small area of sky

The central part of the Coma Berenices cluster covers a roughly circular area about 1 1/2 degrees across. That’s nine times the area of a full moon, which is about 1/2 a degree across. However, the full cluster may extend farther, and numerous other galaxy clusters are in the same area of the sky.

The constellation Coma Berenices lies between the constellations Leo the Lion and Boötes the Herdsman. This part of the sky is the site of the famous open star cluster known as the Coma Berenices star cluster, as well as the most distant galaxy cluster visible through telescopes. To see the star cluster and the galaxy cluster you need a dark sky.

How to find the Coma Berenices galaxy cluster

The galaxy cluster is near the northern border of the constellation Coma Berenices.

Here’s a chart of the constellation Coma Berenices. The blue star indicates the approximate location of the center of the Coma Berenices galaxy cluster. Image via IAU.

The cluster contains thousands of galaxies

The constellation Coma Berenices appears to the eye as a cluster of stars. But a telescope reveals a vast region of distant galaxies in this part of the sky. The chart below gives you an idea of the number of galaxies in that region of the sky.

No idea how twitter renders this image but "faint fuzzy" time! ASI533/8"SCT Alt/Az 50x5s subs looking thru to Coma Cluster of Galaxies. 300Mly away. Looking thru Galactic pole. Like shooting fish in a barrel! SkySafari labels two as IC 4040? Mag 15.4 captured! @BristolAstroSoc pic.twitter.com/pd3ssZn6lE

— Chris Lee FRAS FBIS (@cpl43uk) February 15, 2021

Science of the Coma Berenices galaxy cluster

So, the center of the Coma Berenices galaxy cluster is about 320 million light-years away. And it’s not getting any closer! In fact, the entire cluster is flying away from us at the rate of about more than 15 million mph (24 million kph)!

The Coma Berenices galaxy cluster is one of the most populated galaxy clusters known. And scientists estimate that it contains as many as 10,000 or more members. There are more individual galaxies in this cluster than there are stars visible to the unaided human eye on a clear, dark night.

This section of the Coma Berenices galaxy cluster is about 1/3 of the way from the cluster’s center. The bright spiral galaxy in the upper left is distinctly brighter and bluer than surrounding galaxies and has dusty spiral arms that appear reddish brown against the whiter disk of the galaxy. These are all clues that this galaxy underwent a disturbance at some point in the past. Image via Wikimedia.

A myriad of galaxies

Most galaxies in the central part of the cluster are elliptical. Elliptical galaxies are the result of galaxy mergers. The two brightest members are NGC 4889 and NGC 4874, both of which are giant ellipticals. They are at least two to three times larger than our own Milky Way galaxy. Farther out from the center are several spiral galaxies.

But most galaxies in the Coma Berenices galaxy cluster are dwarf galaxies. Maybe they resemble the Milky Way’s companions, the Large and Small Magellanic Clouds.

Closeup on the majestic face-on spiral galaxy NGC 4911 located deep within the Coma Berenices galaxy cluster. Image via NASA.

Coma Berenices galaxy cluster in history

Too faint for viewing by the human eye (or binoculars and even small telescopes), the ancients could not have seen the galaxy cluster. Hence, it has no associated mythology. However, the Coma Berenices galaxy cluster still has an interesting history.

Not only it is one of the largest and most densely populated clusters of galaxies known, it also led to our discovery of dark matter in our universe. Unseen and mysterious, this matter greatly increases the total mass and gravitational strength of the universe, affecting its evolution and fate.

Dark matter was unknown and unsuspected until Swiss-American astronomer Fritz Zwicky discovered it in the Coma Berenices galaxy cluster in the 1930s. Zwicky tallied up the visible galaxies in the cluster and estimated their masses. Then he observed the motions of galaxies near the edge of the cluster, which are determined by the total gravity (and hence mass) of the cluster. Zwicky found that the mass derived from the latter method greatly exceeded that from visual inspection.

Zwicky knew that if the law of gravity is correct – and there is no reason to doubt it – the only answer could be an additional source of mass, which he called dunkle Materie in German.

Today, scientists see the imprint of dark matter throughout the universe. It’s at least five times more prevalent than the more familiar visible matter, such as the stars and galaxies we can see.

Astronomer Fritz Zwicky 1st predicted the existence of dark matter in the 1930s, following his observations of the Coma Berenices galaxy cluster. Image via Wikimedia Commons.

Coordinates of the Coma Berenices galaxy cluster

The center of the Coma Berenices galaxy cluster is located at approximately RA: 12h 59m, dec: +27° 59′.

Bottom line: Myriads of galaxies, visible only to those with telescopes, shine among the stars of the constellation Coma Berenices. This is the distant Coma Berenices galaxy cluster.

The post The Coma Berenices galaxy cluster, best in April and May first appeared on EarthSky.

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What makes oddly shaped suns and moons on the horizon?

View at EarthSky Community Photos. | Saeed Ahmed Abbasi captured this image of the sun on March 4, 2025, in Pakistan and wrote: “I traveled a few kilometers away from the city to capture the sunset and caught this beauty.” Thank you, Saeed! More below about why you’ll sometimes see oddly shaped suns and moons near the horizon.

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

Oddly shaped suns and moons are great photo opportunities

Sunrises, sunsets, moonrises and moonsets are excellent opportunities to capture a particularly beautiful photograph. When you see them near the horizon, the sun and the moon can look distorted in the most fascinating ways. Their edges may appear jagged. Their bottom areas may flatten out or shrink into a pedestal. Nearby clouds and twilight color help make the artistic view even better.

But why does it happen? What causes the distortion in the appearance of a low sun or moon? The answer is atmospheric refraction, the effect of light traveling through different densities and temperatures of air. Refraction is the same effect that causes a spoon in a glass of water to appear broken in two.

The fact is, when you gaze toward any horizon, you’re looking through more air than when you gaze overhead. It’s this greater quantity of air that causes oddly shaped suns and moons. At zenith (straight up) the atmosphere will be at its thinnest. That’s why professional astronomers prefer to observe their objects of interest as high up on the sky as possible (and as their telescopes allow). And that’s because it diminishes the effects of any atmospheric distortion lower in the sky.

More atmosphere = more distortion

So we know there’s more air in the direction of a horizon. Now consider all the different ways refraction affects a sunrise, sunset, moonrise or moonset.

But it’s not only the amount of atmosphere that plays a role. There’s also the pressure, the temperature and the humidity. They all affect the air density and thereby how much light rays will be bent, or refracted, along their path.

Thus, temperatures varying with different layers of air can spread the light so you see a layered image of the object you’re looking at. In other words, the light refracts more in some layers than in others.

Chart showing how the sun (or moon) becomes distorted when viewed on the distant horizon. Light from objects on the horizon are refracted by the dense atmosphere, so they appear higher in the sky than they are. And the lower portion of the object is lifted higher than the top portion, making the object appear distorted and flattened. Image via Sciencia58/ Wikipedia (CC BY-SA 4.0).

More distortion = oddly shaped suns and moons

The bending of light rays in this manner is known as atmospheric refraction. Without any kind of disturbance, light would travel in a straight line, and give your eye a true image of what you see.

For objects with a small angular size – like stars – atmospheric refraction causes them to twinkle more the closer they are to the horizon.

But what about an object with a fair amount of surface area like the moon and the sun? For them, there is a change in the refractive effect along the height of it. Thus, the upper part travels through less atmosphere than the lower part, which makes the lower part more distorted.

View at EarthSky Community Photos. | Meiying Lee of Taoyuan, Taiwan, shared this composite image and wrote: “At sunset on January 30, 2023, I recorded a mock mirage sunset and green flashes on Mount Hehuan at an altitude of 3,000 meters (9,800 feet). In the mock mirage sunset formed by multiple temperature inversion layers on the high mountain, the sun has various wonderful changes. When the top of the sun falls into the inversion layer, it produces a very obvious green flash.” Thank you, Meiying!

What is a green flash?

When atmospheric refraction is at its most extreme, you might see a mirage. It’s the exact same situation, the light is bent and distorts the image. But here it can be refracted so much that there’s a mirroring effect and you will see drawn out or multiple images. Or it may show displaced images so the moon appears higher on the sky than it actually is.

A well-known mirage for the sun is the sought-after green flash. You can read more about atmospheric phenomena here.

View at Earth Sky Community Photos. | Julia Vaughan captured this image on March 15, 2025, and wrote: “Saturday sunset in Ocean Beach, San Diego, California. The green flash is real, this one has a little blue with it.” Thank you, Julia!

View at EarthSky Community Photos. | Cecille Kennedy on the Oregon Coast captured this image on September 21, 2023. Cecille wrote: “The green flash appeared on top of the fiery red sun as it was setting on the ocean horizon. Over the sun, the birds flying south are brown pelicans migrating to South California and Mexico.” Thank you, Cecille!

Why sunsets are red

Additionally, light of different wavelengths reacts differently. For example, blue light (which has more energy, a shorter wavelength and higher frequency) is more affected by refraction than red light. That means red colors have a larger chance of coming through to you than blue. That’s why sunsets, sunrises and the moon appear redder near the horizon.

The result of refraction is nature’s own form of art, perhaps reminiscent of impressionism. Maybe that is why we find it so appealing. The video below, captured by Mike Cohea, beautifully shows the effect of the thicker atmosphere as the young moon sets over Newport.

So, go out, bring your camera and keep watching the horizon (but never stare directly, or through a camera, at the sun). Then submit your best results to EarthSky Community Photos. We love seeing your pics!

Photos of oddly shaped suns

View at EarthSky Community Photos. | Jim Grant captured this image in San Diego, California, on January 11, 2025, and wrote: “Smoke particulates had been slowly drifting to San Diego from the fires in Los Angeles. The night before the sun was almost obscured, but winds this day blew a lot of heavy smoke away from the coastline. As the sun started setting, I positioned myself to align the sun with the end of the Ocean Beach pier. A combination of layered smoke, clouds and inversion helped create one of the most unique sunsets I have captured in 30 years. And with a green flash.” Thank you, Jim!

View at EarthSky Community Photos. | Christopher Wagner in Los Osos, California, took this photo of the sun on July 13, 2023. Thank you, Christopher! This is a great example of a mock mirage.

Photos of oddly shaped moons

View at EarthSky Community Photos. | Steven Sweet caught this image on March 27, 2025, in Canada and wrote: “Great example of atmospheric refraction causing an illusion below the rising moon.” Thank you, Steven!

View at EarthSky Community Photos. | Cecille Kennedy captured this image on October 23, 2023, in Oregon and wrote: “With a radiant pink blush, the moon over the Pacific Ocean. The first image taken at 7:36 AM. The second at 7:38 AM. The full Hunter Moon rises tonight.” Thank you, Cecille!

Bottom line: The amount of atmosphere between your eye and what you observe determines how much distortion you will see. This phenomenon – atmospheric refraction – is why the sun or moon may appear flattened or jagged near the horizon.

What’s a green flash and how can I see one?

Full moon names of the month and by the season

The post What makes oddly shaped suns and moons on the horizon? first appeared on EarthSky.

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View at EarthSky Community Photos. | Saeed Ahmed Abbasi captured this image of the sun on March 4, 2025, in Pakistan and wrote: “I traveled a few kilometers away from the city to capture the sunset and caught this beauty.” Thank you, Saeed! More below about why you’ll sometimes see oddly shaped suns and moons near the horizon.

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

Oddly shaped suns and moons are great photo opportunities

Sunrises, sunsets, moonrises and moonsets are excellent opportunities to capture a particularly beautiful photograph. When you see them near the horizon, the sun and the moon can look distorted in the most fascinating ways. Their edges may appear jagged. Their bottom areas may flatten out or shrink into a pedestal. Nearby clouds and twilight color help make the artistic view even better.

But why does it happen? What causes the distortion in the appearance of a low sun or moon? The answer is atmospheric refraction, the effect of light traveling through different densities and temperatures of air. Refraction is the same effect that causes a spoon in a glass of water to appear broken in two.

The fact is, when you gaze toward any horizon, you’re looking through more air than when you gaze overhead. It’s this greater quantity of air that causes oddly shaped suns and moons. At zenith (straight up) the atmosphere will be at its thinnest. That’s why professional astronomers prefer to observe their objects of interest as high up on the sky as possible (and as their telescopes allow). And that’s because it diminishes the effects of any atmospheric distortion lower in the sky.

More atmosphere = more distortion

So we know there’s more air in the direction of a horizon. Now consider all the different ways refraction affects a sunrise, sunset, moonrise or moonset.

But it’s not only the amount of atmosphere that plays a role. There’s also the pressure, the temperature and the humidity. They all affect the air density and thereby how much light rays will be bent, or refracted, along their path.

Thus, temperatures varying with different layers of air can spread the light so you see a layered image of the object you’re looking at. In other words, the light refracts more in some layers than in others.

Chart showing how the sun (or moon) becomes distorted when viewed on the distant horizon. Light from objects on the horizon are refracted by the dense atmosphere, so they appear higher in the sky than they are. And the lower portion of the object is lifted higher than the top portion, making the object appear distorted and flattened. Image via Sciencia58/ Wikipedia (CC BY-SA 4.0).

More distortion = oddly shaped suns and moons

The bending of light rays in this manner is known as atmospheric refraction. Without any kind of disturbance, light would travel in a straight line, and give your eye a true image of what you see.

For objects with a small angular size – like stars – atmospheric refraction causes them to twinkle more the closer they are to the horizon.

But what about an object with a fair amount of surface area like the moon and the sun? For them, there is a change in the refractive effect along the height of it. Thus, the upper part travels through less atmosphere than the lower part, which makes the lower part more distorted.

View at EarthSky Community Photos. | Meiying Lee of Taoyuan, Taiwan, shared this composite image and wrote: “At sunset on January 30, 2023, I recorded a mock mirage sunset and green flashes on Mount Hehuan at an altitude of 3,000 meters (9,800 feet). In the mock mirage sunset formed by multiple temperature inversion layers on the high mountain, the sun has various wonderful changes. When the top of the sun falls into the inversion layer, it produces a very obvious green flash.” Thank you, Meiying!

What is a green flash?

When atmospheric refraction is at its most extreme, you might see a mirage. It’s the exact same situation, the light is bent and distorts the image. But here it can be refracted so much that there’s a mirroring effect and you will see drawn out or multiple images. Or it may show displaced images so the moon appears higher on the sky than it actually is.

A well-known mirage for the sun is the sought-after green flash. You can read more about atmospheric phenomena here.

View at Earth Sky Community Photos. | Julia Vaughan captured this image on March 15, 2025, and wrote: “Saturday sunset in Ocean Beach, San Diego, California. The green flash is real, this one has a little blue with it.” Thank you, Julia!

View at EarthSky Community Photos. | Cecille Kennedy on the Oregon Coast captured this image on September 21, 2023. Cecille wrote: “The green flash appeared on top of the fiery red sun as it was setting on the ocean horizon. Over the sun, the birds flying south are brown pelicans migrating to South California and Mexico.” Thank you, Cecille!

Why sunsets are red

Additionally, light of different wavelengths reacts differently. For example, blue light (which has more energy, a shorter wavelength and higher frequency) is more affected by refraction than red light. That means red colors have a larger chance of coming through to you than blue. That’s why sunsets, sunrises and the moon appear redder near the horizon.

The result of refraction is nature’s own form of art, perhaps reminiscent of impressionism. Maybe that is why we find it so appealing. The video below, captured by Mike Cohea, beautifully shows the effect of the thicker atmosphere as the young moon sets over Newport.

So, go out, bring your camera and keep watching the horizon (but never stare directly, or through a camera, at the sun). Then submit your best results to EarthSky Community Photos. We love seeing your pics!

Photos of oddly shaped suns

View at EarthSky Community Photos. | Jim Grant captured this image in San Diego, California, on January 11, 2025, and wrote: “Smoke particulates had been slowly drifting to San Diego from the fires in Los Angeles. The night before the sun was almost obscured, but winds this day blew a lot of heavy smoke away from the coastline. As the sun started setting, I positioned myself to align the sun with the end of the Ocean Beach pier. A combination of layered smoke, clouds and inversion helped create one of the most unique sunsets I have captured in 30 years. And with a green flash.” Thank you, Jim!

View at EarthSky Community Photos. | Christopher Wagner in Los Osos, California, took this photo of the sun on July 13, 2023. Thank you, Christopher! This is a great example of a mock mirage.

Photos of oddly shaped moons

View at EarthSky Community Photos. | Steven Sweet caught this image on March 27, 2025, in Canada and wrote: “Great example of atmospheric refraction causing an illusion below the rising moon.” Thank you, Steven!

View at EarthSky Community Photos. | Cecille Kennedy captured this image on October 23, 2023, in Oregon and wrote: “With a radiant pink blush, the moon over the Pacific Ocean. The first image taken at 7:36 AM. The second at 7:38 AM. The full Hunter Moon rises tonight.” Thank you, Cecille!

Bottom line: The amount of atmosphere between your eye and what you observe determines how much distortion you will see. This phenomenon – atmospheric refraction – is why the sun or moon may appear flattened or jagged near the horizon.

What’s a green flash and how can I see one?

Full moon names of the month and by the season

The post What makes oddly shaped suns and moons on the horizon? first appeared on EarthSky.

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New Comet SWAN25F! See it in binoculars now

The path of Comet SWAN25F looking east-northeast before sunrise. In early April you can use binoculars to see it among the stars of Pegasus the Flying Horse. Image via Eddie Irizarry/ Stellarium.

Meet Comet SWAN25F

There’s a new comet speeding toward the sun, and you can see it with binoculars in the morning sky. SWAN, an instrument aboard the European Space Agency’s SOHO spacecraft that studies the sun, first detected the comet, giving the comet its name of SWAN25F. Australian amateur astronomer Michael Mattiazo was examining the latest images taken by the spacecraft, and on April 1, he reported that a pretty obvious comet was visible in these images.

To see the comet, look toward the east-northeastern horizon just before sunrise. Although the comet is gradually brightening, at the moment you’ll still need binoculars or a small telescope to see it.

The good news is that if the comet survives its perihelion – or closest approach to the sun – in a few weeks, it might be visible during sunset. Just how bright it will be remains to be seen, as comets have shown us they are erratic and unpredictable. But if the comet survives its closest approach to the sun, it would make its transition from the dawn sky to the dusk sky during the first days of May.

By then, the comet’s very high speed will be noticeable when comparing its position during each sunset.

Preliminary observations suggest that closest approach to Earth and to the sun will occur on the same day, on May 1, 2025. The comet will be passing at around 31 million miles from the sun, or just inside of planet Mercury’s average orbit.

At closest approach, the comet’s brightness or magnitude might be between 4.5 to 5. But it will probably be quite close to the horizon.

Look for the comet in Pegasus

During the first days of April, the comet has been inside the Great Square of Pegasus. And it’s moving toward Andromeda.

In fact, one of the stars of the Great Square can help you locate the comet. Look toward the star Alpha Andromedae, or Alpheratz, the brightest of the four corner stars. Comet SWAN25F will pass not far from Alpheratz around April 13, 2025.

Comet SWAN25F is in the constellation Pegasus during April 2025. The comet will be particularly close to one of the stars of the Great Square, Alpheratz, around April 13. Image via Eddie Iriziarry/ Stellarium.

More on Comet SWAN25F

The new comet appears as a small green sphere, which means its coma – or cometary atmosphere – has reactive molecules called diatomic carbon (C2). These appear green when sunlight illuminates the celestial visitor.

Long-exposure images are also showing a faint tail that extends for more than two moon diameters.

Latest reported brightness or magnitude is around 8 to 7.5 and improving (the lower the number, the brighter). Keep checking back, because we’ll keep you updated on its progress!

Bottom line: The new comet SWAN25F is approaching the sun and you can currently see it with binoculars in the morning sky. Keep track of its progress here.

The post New Comet SWAN25F! See it in binoculars now first appeared on EarthSky.

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The path of Comet SWAN25F looking east-northeast before sunrise. In early April you can use binoculars to see it among the stars of Pegasus the Flying Horse. Image via Eddie Irizarry/ Stellarium.

Meet Comet SWAN25F

There’s a new comet speeding toward the sun, and you can see it with binoculars in the morning sky. SWAN, an instrument aboard the European Space Agency’s SOHO spacecraft that studies the sun, first detected the comet, giving the comet its name of SWAN25F. Australian amateur astronomer Michael Mattiazo was examining the latest images taken by the spacecraft, and on April 1, he reported that a pretty obvious comet was visible in these images.

To see the comet, look toward the east-northeastern horizon just before sunrise. Although the comet is gradually brightening, at the moment you’ll still need binoculars or a small telescope to see it.

The good news is that if the comet survives its perihelion – or closest approach to the sun – in a few weeks, it might be visible during sunset. Just how bright it will be remains to be seen, as comets have shown us they are erratic and unpredictable. But if the comet survives its closest approach to the sun, it would make its transition from the dawn sky to the dusk sky during the first days of May.

By then, the comet’s very high speed will be noticeable when comparing its position during each sunset.

Preliminary observations suggest that closest approach to Earth and to the sun will occur on the same day, on May 1, 2025. The comet will be passing at around 31 million miles from the sun, or just inside of planet Mercury’s average orbit.

At closest approach, the comet’s brightness or magnitude might be between 4.5 to 5. But it will probably be quite close to the horizon.

Look for the comet in Pegasus

During the first days of April, the comet has been inside the Great Square of Pegasus. And it’s moving toward Andromeda.

In fact, one of the stars of the Great Square can help you locate the comet. Look toward the star Alpha Andromedae, or Alpheratz, the brightest of the four corner stars. Comet SWAN25F will pass not far from Alpheratz around April 13, 2025.

Comet SWAN25F is in the constellation Pegasus during April 2025. The comet will be particularly close to one of the stars of the Great Square, Alpheratz, around April 13. Image via Eddie Iriziarry/ Stellarium.

More on Comet SWAN25F

The new comet appears as a small green sphere, which means its coma – or cometary atmosphere – has reactive molecules called diatomic carbon (C2). These appear green when sunlight illuminates the celestial visitor.

Long-exposure images are also showing a faint tail that extends for more than two moon diameters.

Latest reported brightness or magnitude is around 8 to 7.5 and improving (the lower the number, the brighter). Keep checking back, because we’ll keep you updated on its progress!

Bottom line: The new comet SWAN25F is approaching the sun and you can currently see it with binoculars in the morning sky. Keep track of its progress here.

The post New Comet SWAN25F! See it in binoculars now first appeared on EarthSky.

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How do bats avoid collisions in massive groups? Now we know!

Watch a video explaining how bats avoid collision when in large groups.

How do bats avoid collisions in massive groups?

It’s well known that bats use echolocation to navigate. That is, they emit a sound, and when this sound hits an object and bounces back, the bat hears the sound and knows how far away the object is. But bats live in colonies of thousands of individuals. When they emerge from their cave at dusk in huge swarms, how do they manage to navigate amid all the noise? A team of scientists from Tel Aviv University in Israel and the Max Planck Institute of Animal Behavior in Germany said on March 26, 2025, that they’ve solved this interesting dilemma.

The researchers tracked dozens of bats in Israel’s Hula Valley and discovered how these animals manage to perform perfect, incident-free flights. The team published its study in the peer-reviewed journal Proceedings of the National Academy of Sciences on March 31, 2025.

Cocktail party nightmare

When bats leave their cave at dusk to stretch their wings and feed, they do so at almost the same time. This situation poses a challenge, as thousands of bats live in a single cave.

Since all the individuals in the cave use the same navigation system — echolocation — a lot of noise is produced, and the sounds emitted by each individual mix with those of others. This hampers these animals’ ability to navigate. Scientists therefore dubbed this massive and chaotic movement the cocktail party nightmare.

Despite all the turmoil, bats do not collide, even in colonies of hundreds of thousands of individuals that leave their home through small openings. The study’s lead author, Aya Goldshtein at the Max Planck Institute of Animal Behavior, joked that bat collisions rarely happen:

You’re almost excited when you witness one.

Bats emerging from the Bracken Bat Cave. Video via Pi3.124/ Wikipedia (CC BY-SA 4.0).

Studying bats in their natural environment

For decades, scientists have tried to figure out how bats are able to pass through such small openings – all at once and so close together – so that they even resemble a kind of flowing liquid.

Some researchers have observed small groups of bats in laboratories. They realized that each bat emitted a sound at a slightly different frequency than the others. Yet this isn’t the solution to the dilemma. This strategy works in a small group, where each bat has its own unique “voice,” but what happens when the colony is huge?

When there are so many individuals producing sounds at once, the voice they need to hear back becomes unrecognizable amid all the noise.

The study’s authors realized that to understand how they move in such large groups, they needed to observe them in their natural environment. So they analyzed the behavior of greater mouse-tailed bats in caves in Israel’s Hula Valley.

Study co-author Yossi Yovel commented:

No one had looked at this situation from the point of view of an individual bat during emergence. How can we understand a behavior if we don’t study it in action?

According to the scientists, the best way to study and understand how an animal behaves is by looking at its natural environment. Image via Tommy Pequinot/ Unsplash.

Bats in the action

The team of scientists attached lightweight trackers to dozens of bats to track their location every second for two years. And not only that, but the trackers also had ultrasonic microphones to hear what the bats were hearing.

Thanks to this combination of high-resolution tracking, ultrasonic recording and sensorimotor computer modeling, the researchers were able to put themselves in the bats’ shoes. The scientists then analyzed the bats in detail as they emerged from cave openings and flew across the landscape in search of food.

With these data, the scientists found that when bats emerge from the caves, the cacophony of sound blocked 94% of echolocations. Scientists call this loss of acoustic information “jamming.” Researchers assumed that, due to these interferences, the bats would collide. But surprisingly, this is not the case.

See bats emerging from a cave by the thousands.

Mystery solved

Just five seconds after leaving the cave, the bats significantly reduced echolocation jamming. This is because the first thing bats do upon leaving is move away from the colony center and disperse, but without losing their group structure.

This behavior was expected. Scientists assumed jamming would decrease as they moved quickly away from the cave. However, they also experienced another significant behavioral change. Upon leaving, they began to emit shorter, softer calls, but with a higher frequency.

The researchers wondered why they would shift their echolocation to a higher frequency. Wouldn’t this increase the problem of jamming and, therefore, the risk of collision? To understand this phenomenon, the researchers had to analyze the situation from a bat’s perspective. Co-author Omer Mazar explained:

Imagine you’re a bat flying through a cluttered space. The most important object you need to know about is the bat directly in front of you. So you should echolocate in such a way that it gives you the most detailed information about only that bat. Sure, you might miss most of the available information because of jamming, but it doesn’t matter because you only need enough detail to avoid crashing into that bat.

In other words, bats adjust their echolocation to obtain more precise information about bats that are nearby, a tactic that ultimately allows them to navigate successfully and avoid colliding with each other.

Hundreds of bats flying out of a cave in Texas.

The importance of observation in nature

In this way, bats increase their distance from the core of the group and adjust their echolocation to navigate safely in the areas most densely populated.

The researchers emphasize that this finding about how bats solve the problem of jamming was possible by studying bats in their natural habitat. Although previous laboratory studies provided a solid foundation, the best way to confirm a behavior is by directly observing it in its real environment. According to Goldshtein:

Theoretical and lab studies of the past have allowed us to imagine the possibilities. But only by putting ourselves, as closely as possible, into the shoes of an animal will we ever be able to understand the challenges they face and what they do to solve them.

Bottom line: Bats navigate in groups of hundreds of thousands individuals, and still, they don’t collide with each other. How do they do it? We finally know!

Source: Onboard recordings reveal how bats maneuver under severe acoustic interference

Via Max Planck Institute of Animal Behavior

Bats, a spooky season icon, are our lifeform of the week

Read more: How do flocking birds move in unison?

The post How do bats avoid collisions in massive groups? Now we know! first appeared on EarthSky.

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Watch a video explaining how bats avoid collision when in large groups.

How do bats avoid collisions in massive groups?

It’s well known that bats use echolocation to navigate. That is, they emit a sound, and when this sound hits an object and bounces back, the bat hears the sound and knows how far away the object is. But bats live in colonies of thousands of individuals. When they emerge from their cave at dusk in huge swarms, how do they manage to navigate amid all the noise? A team of scientists from Tel Aviv University in Israel and the Max Planck Institute of Animal Behavior in Germany said on March 26, 2025, that they’ve solved this interesting dilemma.

The researchers tracked dozens of bats in Israel’s Hula Valley and discovered how these animals manage to perform perfect, incident-free flights. The team published its study in the peer-reviewed journal Proceedings of the National Academy of Sciences on March 31, 2025.

Cocktail party nightmare

When bats leave their cave at dusk to stretch their wings and feed, they do so at almost the same time. This situation poses a challenge, as thousands of bats live in a single cave.

Since all the individuals in the cave use the same navigation system — echolocation — a lot of noise is produced, and the sounds emitted by each individual mix with those of others. This hampers these animals’ ability to navigate. Scientists therefore dubbed this massive and chaotic movement the cocktail party nightmare.

Despite all the turmoil, bats do not collide, even in colonies of hundreds of thousands of individuals that leave their home through small openings. The study’s lead author, Aya Goldshtein at the Max Planck Institute of Animal Behavior, joked that bat collisions rarely happen:

You’re almost excited when you witness one.

Bats emerging from the Bracken Bat Cave. Video via Pi3.124/ Wikipedia (CC BY-SA 4.0).

Studying bats in their natural environment

For decades, scientists have tried to figure out how bats are able to pass through such small openings – all at once and so close together – so that they even resemble a kind of flowing liquid.

Some researchers have observed small groups of bats in laboratories. They realized that each bat emitted a sound at a slightly different frequency than the others. Yet this isn’t the solution to the dilemma. This strategy works in a small group, where each bat has its own unique “voice,” but what happens when the colony is huge?

When there are so many individuals producing sounds at once, the voice they need to hear back becomes unrecognizable amid all the noise.

The study’s authors realized that to understand how they move in such large groups, they needed to observe them in their natural environment. So they analyzed the behavior of greater mouse-tailed bats in caves in Israel’s Hula Valley.

Study co-author Yossi Yovel commented:

No one had looked at this situation from the point of view of an individual bat during emergence. How can we understand a behavior if we don’t study it in action?

According to the scientists, the best way to study and understand how an animal behaves is by looking at its natural environment. Image via Tommy Pequinot/ Unsplash.

Bats in the action

The team of scientists attached lightweight trackers to dozens of bats to track their location every second for two years. And not only that, but the trackers also had ultrasonic microphones to hear what the bats were hearing.

Thanks to this combination of high-resolution tracking, ultrasonic recording and sensorimotor computer modeling, the researchers were able to put themselves in the bats’ shoes. The scientists then analyzed the bats in detail as they emerged from cave openings and flew across the landscape in search of food.

With these data, the scientists found that when bats emerge from the caves, the cacophony of sound blocked 94% of echolocations. Scientists call this loss of acoustic information “jamming.” Researchers assumed that, due to these interferences, the bats would collide. But surprisingly, this is not the case.

See bats emerging from a cave by the thousands.

Mystery solved

Just five seconds after leaving the cave, the bats significantly reduced echolocation jamming. This is because the first thing bats do upon leaving is move away from the colony center and disperse, but without losing their group structure.

This behavior was expected. Scientists assumed jamming would decrease as they moved quickly away from the cave. However, they also experienced another significant behavioral change. Upon leaving, they began to emit shorter, softer calls, but with a higher frequency.

The researchers wondered why they would shift their echolocation to a higher frequency. Wouldn’t this increase the problem of jamming and, therefore, the risk of collision? To understand this phenomenon, the researchers had to analyze the situation from a bat’s perspective. Co-author Omer Mazar explained:

Imagine you’re a bat flying through a cluttered space. The most important object you need to know about is the bat directly in front of you. So you should echolocate in such a way that it gives you the most detailed information about only that bat. Sure, you might miss most of the available information because of jamming, but it doesn’t matter because you only need enough detail to avoid crashing into that bat.

In other words, bats adjust their echolocation to obtain more precise information about bats that are nearby, a tactic that ultimately allows them to navigate successfully and avoid colliding with each other.

Hundreds of bats flying out of a cave in Texas.

The importance of observation in nature

In this way, bats increase their distance from the core of the group and adjust their echolocation to navigate safely in the areas most densely populated.

The researchers emphasize that this finding about how bats solve the problem of jamming was possible by studying bats in their natural habitat. Although previous laboratory studies provided a solid foundation, the best way to confirm a behavior is by directly observing it in its real environment. According to Goldshtein:

Theoretical and lab studies of the past have allowed us to imagine the possibilities. But only by putting ourselves, as closely as possible, into the shoes of an animal will we ever be able to understand the challenges they face and what they do to solve them.

Bottom line: Bats navigate in groups of hundreds of thousands individuals, and still, they don’t collide with each other. How do they do it? We finally know!

Source: Onboard recordings reveal how bats maneuver under severe acoustic interference

Via Max Planck Institute of Animal Behavior

Bats, a spooky season icon, are our lifeform of the week

Read more: How do flocking birds move in unison?

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Dark skies of Paranal Observatory in Chile are under threat

The European Southern Observatory’s Paranal Observatory lies under some of the darkest and clearest skies in the world, in Chile’s Atacama Desert. Now a new construction project is threatening to cause irreparable damage to the views of deep space, visible from this pristine site. In this image, Jupiter is the bright object near ESO Photo Ambassador Petr Horálek (standing at center). The telescopes in this view are the 4 Unit Telescopes (UTs) that comprise ESO’s Very Large Telescope VLT. Also in this shot are 4 smaller Auxiliary Telescopes (ATs). Image via ESO/ P. Horálek.

Dark skies of Paranal Observatory under threat

The night sky over the European Southern Observatory’s Paranal Observatory in Chile is said to be the darkest and clearest over any astronomical observatory in the world. Astronomical data gathered under these pristine skies let astronomers present the first image of an exoplanet, and confirm the accelerated expansion of the universe. But now, according to ESO, a new industrial megaproject is threatening the observatory’s dark skies. A preliminary analysis by ESO suggests the project would cause “devastating and irreversible” harm to the region’s night sky.

That megaproject is a massive industrial complex by AES Andes, based in Santiago, Chile. This company is a subsidiary of the U.S. power company AES Corporation. According to ESO, the AES Andes complex would be city sized (more than 7,400 acres) and lie just a few kilometers from Paranal Observatory. The ESO analysis follows an environmental assessment, submited by AES Andes on December 24, 2024.

AES Andes’ project is called INNA, for Infraestructura Energética para la Generación de Hidrogeno y Amoníaco Verde. The project seeks to make use of the solar and wind resources in the area.

ESO’s director general Xavier Barcons said:

The proximity of the AES Andes industrial megaproject to Paranal poses a critical risk to the most pristine night skies on the planet. Dust emissions during construction, increased atmospheric turbulence, and especially light pollution will irreparably impact the capabilities for astronomical observation, which have thus far attracted multi-billion-Euro investments by the governments of the ESO Member States.

View larger. | This map of the region shows the location of Paranal Observatory in the Atacama Desert in Chile along with the proposed industrial complex. Image via ESO.

The results of the analysis

The INNA project would include construction of a port, ammonia and hydrogen production plants and thousands of electricity generation units. The analysis said that light pollution would increase by at least 35% above the VLT and by more than 50% above the south site of the Cherenkov Telescope Array Observatory (CTAO-South). The increase in air turbulence and vibrations would further cause problems. For example, the Extremely Large Telescope, currently under construction, is extremely sensitive to even the smallest vibrations. The nearby INNA project wind turbines would impair its abilities. How would this harm astronomers’ research? One example – described by Paul Scott Anderson of EarthSky – is that, after its completion, the ELT would have the capability to find alien life in just hours. Will that still be true if AES Andes carries out its industrial megaproject?

The impact of light pollution on these telescopes even puts our planet at risk. A representative of ESO, Itziar de Gregorio-Monsalvo, said:

With a brighter sky, we severely limit our ability to … monitor asteroids that could cause damage to our planet. We build the largest and most powerful telescopes, in the best place on Earth for astronomy, to enable astronomers worldwide to see what no one has ever seen before. Light pollution from projects like INNA doesn’t just hinder research, it steals our shared view of the universe.

The director of operations for ESO, Andreas Kaufer, said:

The light-pollution figures we are reporting assume that the project will install the most modern available luminaries in a way that minimizes light pollution. However, we are concerned that the inventory of light sources planned by AES is not complete and fit for purpose. In that case, our already alarming results would underestimate the potential impact of the INNA project on the Paranal sky brightness.

Request to move the project

Barcons said:

ESO and its Member States are fully supportive of energy decarbonization. For us Chile should not have to make a choice between hosting the most powerful astronomical observatories and developing green-energy projects. Both are declared strategic priorities by the country and are fully compatible — if the different facilities are located at sufficient distances from one another.

ESO also has an executive summary of the report on the environmental impact assessment. ESO said:

The relocation of this project remains the only effective way to prevent irreversible damage to Paranal’s unique skies.

Chilean authorities will look at the full technical report in late April 2025.

Views from Paranal Observatory

This image showcases ESO’s Paranal Observatory and the Very Large Telescope (VLT). They sit at an altitude of 8,530 feet (2,600 meters) in the Atacama Desert in Chile. The snow-capped peak in the background is the volcano Llullaillaco, on the Argentinean border. ESO said, “This image is a testimony of the magnificent quality of the air and the ideal conditions for observing at this remote site.” Image via ESO/ G.Hüdepohl.

A laser shoots out of one of the Unit Telescopes of the Very Large Telescope (VLT). Image via ESO/ Yuri Beletsky.

This scene from Paranal Observatory shows an Auxiliary Telescope in the foreground between the Magellanic Clouds as the Milky Way arches overhead. Image via ESO/ R. Wesson.

Bottom line: The Atacama Desert in Chile, where ESO’s Paranal Observatory sits, has some of the clearest and darkest skies in the world. Groundbreaking astronomical discoveries have come from the observatories there. But a new industrial complex threatens the observatory with devastating and irreversible impacts.

Via ESO

The post Dark skies of Paranal Observatory in Chile are under threat first appeared on EarthSky.

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The European Southern Observatory’s Paranal Observatory lies under some of the darkest and clearest skies in the world, in Chile’s Atacama Desert. Now a new construction project is threatening to cause irreparable damage to the views of deep space, visible from this pristine site. In this image, Jupiter is the bright object near ESO Photo Ambassador Petr Horálek (standing at center). The telescopes in this view are the 4 Unit Telescopes (UTs) that comprise ESO’s Very Large Telescope VLT. Also in this shot are 4 smaller Auxiliary Telescopes (ATs). Image via ESO/ P. Horálek.

Dark skies of Paranal Observatory under threat

The night sky over the European Southern Observatory’s Paranal Observatory in Chile is said to be the darkest and clearest over any astronomical observatory in the world. Astronomical data gathered under these pristine skies let astronomers present the first image of an exoplanet, and confirm the accelerated expansion of the universe. But now, according to ESO, a new industrial megaproject is threatening the observatory’s dark skies. A preliminary analysis by ESO suggests the project would cause “devastating and irreversible” harm to the region’s night sky.

That megaproject is a massive industrial complex by AES Andes, based in Santiago, Chile. This company is a subsidiary of the U.S. power company AES Corporation. According to ESO, the AES Andes complex would be city sized (more than 7,400 acres) and lie just a few kilometers from Paranal Observatory. The ESO analysis follows an environmental assessment, submited by AES Andes on December 24, 2024.

AES Andes’ project is called INNA, for Infraestructura Energética para la Generación de Hidrogeno y Amoníaco Verde. The project seeks to make use of the solar and wind resources in the area.

ESO’s director general Xavier Barcons said:

The proximity of the AES Andes industrial megaproject to Paranal poses a critical risk to the most pristine night skies on the planet. Dust emissions during construction, increased atmospheric turbulence, and especially light pollution will irreparably impact the capabilities for astronomical observation, which have thus far attracted multi-billion-Euro investments by the governments of the ESO Member States.

View larger. | This map of the region shows the location of Paranal Observatory in the Atacama Desert in Chile along with the proposed industrial complex. Image via ESO.

The results of the analysis

The INNA project would include construction of a port, ammonia and hydrogen production plants and thousands of electricity generation units. The analysis said that light pollution would increase by at least 35% above the VLT and by more than 50% above the south site of the Cherenkov Telescope Array Observatory (CTAO-South). The increase in air turbulence and vibrations would further cause problems. For example, the Extremely Large Telescope, currently under construction, is extremely sensitive to even the smallest vibrations. The nearby INNA project wind turbines would impair its abilities. How would this harm astronomers’ research? One example – described by Paul Scott Anderson of EarthSky – is that, after its completion, the ELT would have the capability to find alien life in just hours. Will that still be true if AES Andes carries out its industrial megaproject?

The impact of light pollution on these telescopes even puts our planet at risk. A representative of ESO, Itziar de Gregorio-Monsalvo, said:

With a brighter sky, we severely limit our ability to … monitor asteroids that could cause damage to our planet. We build the largest and most powerful telescopes, in the best place on Earth for astronomy, to enable astronomers worldwide to see what no one has ever seen before. Light pollution from projects like INNA doesn’t just hinder research, it steals our shared view of the universe.

The director of operations for ESO, Andreas Kaufer, said:

The light-pollution figures we are reporting assume that the project will install the most modern available luminaries in a way that minimizes light pollution. However, we are concerned that the inventory of light sources planned by AES is not complete and fit for purpose. In that case, our already alarming results would underestimate the potential impact of the INNA project on the Paranal sky brightness.

Request to move the project

Barcons said:

ESO and its Member States are fully supportive of energy decarbonization. For us Chile should not have to make a choice between hosting the most powerful astronomical observatories and developing green-energy projects. Both are declared strategic priorities by the country and are fully compatible — if the different facilities are located at sufficient distances from one another.

ESO also has an executive summary of the report on the environmental impact assessment. ESO said:

The relocation of this project remains the only effective way to prevent irreversible damage to Paranal’s unique skies.

Chilean authorities will look at the full technical report in late April 2025.

Views from Paranal Observatory

This image showcases ESO’s Paranal Observatory and the Very Large Telescope (VLT). They sit at an altitude of 8,530 feet (2,600 meters) in the Atacama Desert in Chile. The snow-capped peak in the background is the volcano Llullaillaco, on the Argentinean border. ESO said, “This image is a testimony of the magnificent quality of the air and the ideal conditions for observing at this remote site.” Image via ESO/ G.Hüdepohl.

A laser shoots out of one of the Unit Telescopes of the Very Large Telescope (VLT). Image via ESO/ Yuri Beletsky.

This scene from Paranal Observatory shows an Auxiliary Telescope in the foreground between the Magellanic Clouds as the Milky Way arches overhead. Image via ESO/ R. Wesson.

Bottom line: The Atacama Desert in Chile, where ESO’s Paranal Observatory sits, has some of the clearest and darkest skies in the world. Groundbreaking astronomical discoveries have come from the observatories there. But a new industrial complex threatens the observatory with devastating and irreversible impacts.

Via ESO

The post Dark skies of Paranal Observatory in Chile are under threat first appeared on EarthSky.

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