A comet breaks apart in this series of images from NASA’s Hubble Space Telescope. The comet was C/2025 K1 (ATLAS) (not to be confused with the interstellar comet 3I/ATLAS). These images document 3 consecutive days: November 8, 9 and 10, 2025. It’s the first time Hubble witnessed a comet so early in the process of breaking up. Image via NASA/ ESA/ Dennis Bodewits (AU). Image Processing: Joseph DePasquale (STScI).
Hubble has captured a rare view of a comet breaking apart. It captured these images about a month after the comet made its closest pass by the sun.
The discovery was a happy accident. The scientist’s original target was a different comet. But this is the first time Hubble has caught a fragmenting comet so close to when it actually fell apart.
The breakup offers scientists a glimpse of pristine material, helping them study the early solar system’s building blocks.
In a happy twist of fate, NASA’s Hubble Space Telescope just witnessed a comet in the act of breaking apart. The chance of that happening while Hubble watched is extraordinarily minuscule. The comet K1, whose full name is C/2025 K1 (ATLAS) – not to be confused with interstellar comet 3I/ATLAS – was not the original target of the Hubble study.
Co-investigator John Noonan, a research professor in the Department of Physics at Auburn University in Alabama, said:
Sometimes the best science happens by accident. This comet got observed because our original comet was not viewable due to some new technical constraints after we won our proposal. We had to find a new target … and right when we observed it, it happened to break apart, which is the slimmest of slim chances.
Noonan didn’t know K1 was fragmenting until he viewed the images the day after Hubble took them. Noonan said:
While I was taking an initial look at the data, I saw that there were four comets in those images when we only proposed to look at one. So we knew this was something really, really special.
This is an experiment the researchers always wanted to do with Hubble. They had proposed many Hubble observations to catch a comet breaking up. Unfortunately, these are very difficult to schedule, and they were never successful. Principal investigator Dennis Bodewits, also a professor in Auburn University’s Department of Physics, said:
The irony is now we’re just studying a regular comet and it crumbles in front of our eyes.
Comets are leftovers of the era of solar system formation, so they’re made of ‘old stuff’: the primordial materials that made our solar system. But they are not pristine. They’ve been heated; they’ve been irradiated by the sun and by cosmic rays. So, when looking at a comet’s composition, the question we always have is, ‘Is this a primitive property or is this due to evolution?’ By cracking open a comet, you can see the ancient material that has not been processed.
This diagram shows the path Comet C/2025 K1 (ATLAS), or K1, took as it swung past the sun and began its journey out of the solar system. NASA’s Hubble Space Telescope captured the inset image of the fragmenting comet just a month after K1’s closest approach to the sun. Illustration via NASA/ ESA/ Ralf Crawford (STScI).
A closer look at a solar system breakup
Hubble caught K1 fragmenting into at least four pieces. Each had a distinct coma, which is the fuzzy envelope of gas and dust that surrounds a comet’s icy nucleus. Hubble cleanly resolved the fragments. But to ground-based telescopes at the time, they only appeared as barely distinguishable, bright blobs.
Hubble took its images just a month after K1’s closest approach to the sun, called perihelion. The comet’s perihelion was inside Mercury’s orbit, about one-third the distance of the Earth from the sun. During perihelion, a comet experiences its most intense heating and maximum stress. Just past perihelion is when some long-period comets like K1 tend to fall apart.
Before it fragmented, K1 was likely a bit larger than an average comet, probably around 5 miles (8 km) across. The team estimates the comet began to disintegrate eight days before Hubble viewed it. Hubble took three 20-second images, one on each day from November 8 through 10, 2025. As it watched the comet, one of K1’s smaller pieces also broke up.
Because Hubble’s sharp vision can distinguish extremely fine details, the team could trace the history of the fragments back to when they were one piece. That allowed them to reconstruct the timeline. But in doing so, they uncovered a mystery: Why was there a delay between when the comet broke up and when bright outbursts were seen from the ground? When the comet fragmented and exposed fresh ice, why didn’t it brighten almost instantaneously?
Exploring the mysteries of comet K1 ATLAS
The team has some theories. Most of a comet’s brightness is sunlight reflected off of dust grains. But when a comet cracks open, it reveals pure ice. Maybe a layer of dry dust needs to form over the pure ice and then blow off. Or maybe heat needs to get below the surface, build up pressure, and then eject an expanding shell of dust. Noonan said:
Never before has Hubble caught a fragmenting comet this close to when it actually fell apart. Most of the time, it’s a few weeks to a month later. And in this case, we were able to see it just days after. This is telling us something very important about the physics of what’s happening at the comet’s surface. We may be seeing the timescale it takes to form a substantial dust layer that can then be ejected by the gas.
The research team is looking forward to finishing the analysis of the gases to come from the comet. Already, ground-based analysis shows that K1 is chemically very strange. It is significantly depleted in carbon compared with other comets. Spectroscopic analysis from Hubble’s STIS (Space Telescope Imaging Spectrograph) and COS (Cosmic Origins Spectrograph) instruments is likely to reveal much more about the composition of K1 and the very origins of our solar system.
The comet K1 is now a collection of fragments about 250 million miles from Earth. Located in the constellation Pisces, it is heading out of the solar system, not likely to ever return.
Bottom line: Hubble captures a rare moment as a comet breaks apart after passing close to our sun. The images revealing ancient material from the early solar system.
A comet breaks apart in this series of images from NASA’s Hubble Space Telescope. The comet was C/2025 K1 (ATLAS) (not to be confused with the interstellar comet 3I/ATLAS). These images document 3 consecutive days: November 8, 9 and 10, 2025. It’s the first time Hubble witnessed a comet so early in the process of breaking up. Image via NASA/ ESA/ Dennis Bodewits (AU). Image Processing: Joseph DePasquale (STScI).
Hubble has captured a rare view of a comet breaking apart. It captured these images about a month after the comet made its closest pass by the sun.
The discovery was a happy accident. The scientist’s original target was a different comet. But this is the first time Hubble has caught a fragmenting comet so close to when it actually fell apart.
The breakup offers scientists a glimpse of pristine material, helping them study the early solar system’s building blocks.
In a happy twist of fate, NASA’s Hubble Space Telescope just witnessed a comet in the act of breaking apart. The chance of that happening while Hubble watched is extraordinarily minuscule. The comet K1, whose full name is C/2025 K1 (ATLAS) – not to be confused with interstellar comet 3I/ATLAS – was not the original target of the Hubble study.
Co-investigator John Noonan, a research professor in the Department of Physics at Auburn University in Alabama, said:
Sometimes the best science happens by accident. This comet got observed because our original comet was not viewable due to some new technical constraints after we won our proposal. We had to find a new target … and right when we observed it, it happened to break apart, which is the slimmest of slim chances.
Noonan didn’t know K1 was fragmenting until he viewed the images the day after Hubble took them. Noonan said:
While I was taking an initial look at the data, I saw that there were four comets in those images when we only proposed to look at one. So we knew this was something really, really special.
This is an experiment the researchers always wanted to do with Hubble. They had proposed many Hubble observations to catch a comet breaking up. Unfortunately, these are very difficult to schedule, and they were never successful. Principal investigator Dennis Bodewits, also a professor in Auburn University’s Department of Physics, said:
The irony is now we’re just studying a regular comet and it crumbles in front of our eyes.
Comets are leftovers of the era of solar system formation, so they’re made of ‘old stuff’: the primordial materials that made our solar system. But they are not pristine. They’ve been heated; they’ve been irradiated by the sun and by cosmic rays. So, when looking at a comet’s composition, the question we always have is, ‘Is this a primitive property or is this due to evolution?’ By cracking open a comet, you can see the ancient material that has not been processed.
This diagram shows the path Comet C/2025 K1 (ATLAS), or K1, took as it swung past the sun and began its journey out of the solar system. NASA’s Hubble Space Telescope captured the inset image of the fragmenting comet just a month after K1’s closest approach to the sun. Illustration via NASA/ ESA/ Ralf Crawford (STScI).
A closer look at a solar system breakup
Hubble caught K1 fragmenting into at least four pieces. Each had a distinct coma, which is the fuzzy envelope of gas and dust that surrounds a comet’s icy nucleus. Hubble cleanly resolved the fragments. But to ground-based telescopes at the time, they only appeared as barely distinguishable, bright blobs.
Hubble took its images just a month after K1’s closest approach to the sun, called perihelion. The comet’s perihelion was inside Mercury’s orbit, about one-third the distance of the Earth from the sun. During perihelion, a comet experiences its most intense heating and maximum stress. Just past perihelion is when some long-period comets like K1 tend to fall apart.
Before it fragmented, K1 was likely a bit larger than an average comet, probably around 5 miles (8 km) across. The team estimates the comet began to disintegrate eight days before Hubble viewed it. Hubble took three 20-second images, one on each day from November 8 through 10, 2025. As it watched the comet, one of K1’s smaller pieces also broke up.
Because Hubble’s sharp vision can distinguish extremely fine details, the team could trace the history of the fragments back to when they were one piece. That allowed them to reconstruct the timeline. But in doing so, they uncovered a mystery: Why was there a delay between when the comet broke up and when bright outbursts were seen from the ground? When the comet fragmented and exposed fresh ice, why didn’t it brighten almost instantaneously?
Exploring the mysteries of comet K1 ATLAS
The team has some theories. Most of a comet’s brightness is sunlight reflected off of dust grains. But when a comet cracks open, it reveals pure ice. Maybe a layer of dry dust needs to form over the pure ice and then blow off. Or maybe heat needs to get below the surface, build up pressure, and then eject an expanding shell of dust. Noonan said:
Never before has Hubble caught a fragmenting comet this close to when it actually fell apart. Most of the time, it’s a few weeks to a month later. And in this case, we were able to see it just days after. This is telling us something very important about the physics of what’s happening at the comet’s surface. We may be seeing the timescale it takes to form a substantial dust layer that can then be ejected by the gas.
The research team is looking forward to finishing the analysis of the gases to come from the comet. Already, ground-based analysis shows that K1 is chemically very strange. It is significantly depleted in carbon compared with other comets. Spectroscopic analysis from Hubble’s STIS (Space Telescope Imaging Spectrograph) and COS (Cosmic Origins Spectrograph) instruments is likely to reveal much more about the composition of K1 and the very origins of our solar system.
The comet K1 is now a collection of fragments about 250 million miles from Earth. Located in the constellation Pisces, it is heading out of the solar system, not likely to ever return.
Bottom line: Hubble captures a rare moment as a comet breaks apart after passing close to our sun. The images revealing ancient material from the early solar system.
This map shows the forecast high temperatures for Wednesday, March 18, through Sunday, March 22, 2026. If these high temperatures materialize, they will break the record highs for these locations. Read more about the early season heatwave hitting this week. Image via NWS.
Early season heatwave in US to bring possible record temps
An early spring heatwave is set to bring record temperatures for this time of year to much of the U.S. this week.
Thanks to a strong ridge of high pressure centered over the American Southwest, temperatures in the region could hit 100 degrees F (38 C) at the earliest time of year since 1988. Across California and the desert southwest, temperatures are forecast to be 20 to 30 degrees Fahrenheit (11 to 17°C) warmer than normal for this time of year. The heatwave will then expand east, toward the Rockies and Great Plains.
This heatwave is going to be persistent. The heat dome is already building. Some areas can expect record-high temps all the way through Sunday. The triple-digit heat may ease by early next week. However, forecasts call for temperatures to stay above average for the next week and a half. And that’s not just in the southwestern United States but across most of the country.
The Climate Prediction Center has outlined a majority of the United States for a higher probability of warmer-than-average temperatures through March 27, 2026. This doesn’t mean most of the country will break high temperature records or soar into the triple digits. But it does mean temperatures have a better chance of being warmer than normal for that region during this time frame.
The 6-10 day temperature outlook from the Climate Prediction Center. Image via CPC.
Heat advisories
Normally associated with summer, heat advisories are issued by local weather service offices whenever they expect the heat to be a danger to health and safety.
In the southwestern United States, an Extreme Heat Warning is already out for parts of Southern California into southern Arizona. This means meteorologists expect extremely dangerous heat or it’s already occurring. During an Extreme Heat Warning, you shouldn’t go outside during the hottest part of the day unless absolutely necessary. If you cannot avoid being outside, stay well-hydrated with water, take frequent breaks in the shade, but find air-conditioning as often as possible.
An Extreme Heat Warning is in effect for the southwestern United States. Image via NWS Phoenix.
When hot weather is on the way, you may get an Extreme Heat Watch. This means the extreme, dangerous heat is possible but hasn’t arrived just yet. The NWS issues these watches so you can prepare for dangerous heat. Steps to take include having a backup for outdoor plans, finding the closest cooling center and checking in on family and friends.
Arizona in the bull’s-eye
For Phoenix, Arizona, the National Weather Service is forecasting a high temperature for Wednesday, March 18, 2026, of 102 F (39 C). This would not only break the high temperature record for the day, but it would be the earliest 100-degree day by nearly 40 years.
The earliest Phoenix has ever hit the 100-degree mark was March 26, 1988. And it’s almost two months ahead of when Phoenix typically experiences its first triple-digit temp. The average first 100-degree day is May 2. That’s based on the 30-year climate data for that area. The dangerous heat will persist in the Southwest through the weekend.
Forecasters call for high temperatures climbing to as hot as 106 F (41 C) on Friday and Saturday.
Expect a stretch of record high temperatures in Arizona through the end of the week. Image via NWS Phoenix.According to the National Weather Service in Phoenix, the city could break its all-time high temperatures for both March and April this week. The previous earliest-ever heat warning was issued April 26–30, 2020, and Phoenix now faces an extreme heat warning. Image via NWS.
Staying safe in extreme heat
Staying safe in extreme heat can vary a bit depending on your situation. But the main idea is to avoid the heat as much as possible. If you are able to stay inside, ideally in air-conditioning, this is your best option. But as mentioned, if you cannot avoid the hot weather, there are things you can do. Take frequent breaks in the shade. Make sure you’re staying hydrated. Wear light color, loose-fitting clothing. And pay close attention to how you’re feeling as the day goes on.
If you, or someone you are with, is sweating heavily, feeling weak, tired, dizzy or nauseated, these could be signs of heat exhaustion. Immediately move yourself or the other person into A/C. Loosen their clothing, give them sips of cool water and put cold compresses on their body.
If someone is acting confused and slurring their speech, has red and hot skin or passes out, this is likely a heat stroke. They need medical attention immediately! Call 911. While you wait for help to arrive, move the person to A/C, add cool compresses to lower their body temperature, but do not give them anything to drink.
The heat can also be more dangerous to the very young, the very old, people with chronic medical conditions and pregnant women. In addition, the unhoused and lower income communities, who may not be able to afford to run their air-conditioning, are also at risk. Check on your friends, family and neighbors before, during and after extreme heat.
Early season heat is expected in the southwest, possibly the first 100°F of the year. Image via Pexels.
Bottom line: Forecasters are calling for an early season heatwave in the southwestern United States, spreading east. Get details here. Plus how to prepare before the heat hits.
This map shows the forecast high temperatures for Wednesday, March 18, through Sunday, March 22, 2026. If these high temperatures materialize, they will break the record highs for these locations. Read more about the early season heatwave hitting this week. Image via NWS.
Early season heatwave in US to bring possible record temps
An early spring heatwave is set to bring record temperatures for this time of year to much of the U.S. this week.
Thanks to a strong ridge of high pressure centered over the American Southwest, temperatures in the region could hit 100 degrees F (38 C) at the earliest time of year since 1988. Across California and the desert southwest, temperatures are forecast to be 20 to 30 degrees Fahrenheit (11 to 17°C) warmer than normal for this time of year. The heatwave will then expand east, toward the Rockies and Great Plains.
This heatwave is going to be persistent. The heat dome is already building. Some areas can expect record-high temps all the way through Sunday. The triple-digit heat may ease by early next week. However, forecasts call for temperatures to stay above average for the next week and a half. And that’s not just in the southwestern United States but across most of the country.
The Climate Prediction Center has outlined a majority of the United States for a higher probability of warmer-than-average temperatures through March 27, 2026. This doesn’t mean most of the country will break high temperature records or soar into the triple digits. But it does mean temperatures have a better chance of being warmer than normal for that region during this time frame.
The 6-10 day temperature outlook from the Climate Prediction Center. Image via CPC.
Heat advisories
Normally associated with summer, heat advisories are issued by local weather service offices whenever they expect the heat to be a danger to health and safety.
In the southwestern United States, an Extreme Heat Warning is already out for parts of Southern California into southern Arizona. This means meteorologists expect extremely dangerous heat or it’s already occurring. During an Extreme Heat Warning, you shouldn’t go outside during the hottest part of the day unless absolutely necessary. If you cannot avoid being outside, stay well-hydrated with water, take frequent breaks in the shade, but find air-conditioning as often as possible.
An Extreme Heat Warning is in effect for the southwestern United States. Image via NWS Phoenix.
When hot weather is on the way, you may get an Extreme Heat Watch. This means the extreme, dangerous heat is possible but hasn’t arrived just yet. The NWS issues these watches so you can prepare for dangerous heat. Steps to take include having a backup for outdoor plans, finding the closest cooling center and checking in on family and friends.
Arizona in the bull’s-eye
For Phoenix, Arizona, the National Weather Service is forecasting a high temperature for Wednesday, March 18, 2026, of 102 F (39 C). This would not only break the high temperature record for the day, but it would be the earliest 100-degree day by nearly 40 years.
The earliest Phoenix has ever hit the 100-degree mark was March 26, 1988. And it’s almost two months ahead of when Phoenix typically experiences its first triple-digit temp. The average first 100-degree day is May 2. That’s based on the 30-year climate data for that area. The dangerous heat will persist in the Southwest through the weekend.
Forecasters call for high temperatures climbing to as hot as 106 F (41 C) on Friday and Saturday.
Expect a stretch of record high temperatures in Arizona through the end of the week. Image via NWS Phoenix.According to the National Weather Service in Phoenix, the city could break its all-time high temperatures for both March and April this week. The previous earliest-ever heat warning was issued April 26–30, 2020, and Phoenix now faces an extreme heat warning. Image via NWS.
Staying safe in extreme heat
Staying safe in extreme heat can vary a bit depending on your situation. But the main idea is to avoid the heat as much as possible. If you are able to stay inside, ideally in air-conditioning, this is your best option. But as mentioned, if you cannot avoid the hot weather, there are things you can do. Take frequent breaks in the shade. Make sure you’re staying hydrated. Wear light color, loose-fitting clothing. And pay close attention to how you’re feeling as the day goes on.
If you, or someone you are with, is sweating heavily, feeling weak, tired, dizzy or nauseated, these could be signs of heat exhaustion. Immediately move yourself or the other person into A/C. Loosen their clothing, give them sips of cool water and put cold compresses on their body.
If someone is acting confused and slurring their speech, has red and hot skin or passes out, this is likely a heat stroke. They need medical attention immediately! Call 911. While you wait for help to arrive, move the person to A/C, add cool compresses to lower their body temperature, but do not give them anything to drink.
The heat can also be more dangerous to the very young, the very old, people with chronic medical conditions and pregnant women. In addition, the unhoused and lower income communities, who may not be able to afford to run their air-conditioning, are also at risk. Check on your friends, family and neighbors before, during and after extreme heat.
Early season heat is expected in the southwest, possibly the first 100°F of the year. Image via Pexels.
Bottom line: Forecasters are calling for an early season heatwave in the southwestern United States, spreading east. Get details here. Plus how to prepare before the heat hits.
View at EarthSky Community Photos. |Rupesh Sangoi in Mumbai, India, captured separate images of the sunrise, showing the sun’s movement along the horizon, between the June and December solstices and on the equinoxes. Rupesh wrote: “Did this for over a year, at sunrise.” Glorious composite, Rupesh! Thank you.
The sun’s movement from day to day along your horizon – at the sunrise or sunset point – is most noticeable around the equinoxes. And many streets in the U.S. and in other parts of the world are oriented either north-south or east-west. So, just by looking out the doorway of your home, you might be able to watch the progress of the sun as it slides from south to north in the weeks and months following the March equinox.
On the equinox, the sun rises directly in the east and sets directly in the west. You can see it move quickly further north each day afterward. No grid of streets to help you? Try tracking the sun’s progress along the horizon by placing bits of tape on an east- or west-facing window of your home. Or just find a clear spot – a place where you can see the horizon – and stand in the same spot whenever you watch the sunrise or sunset. You’ll notice the sun’s movement with respect to trees and other objects in the foreground.
Just be sure to observe from the exact same location every day. It’s enough to note the sunrise or sunset point every week or 10 days. You’ll easily see the sun’s northward shift between now and the June solstice.
Then track between the solstices
What happens at the solstice? At mid-northern latitudes, there’s a two- to three-week time period where you probably won’t discern any movement of the sun along the horizon. That’s where the word solstice comes from. Solstice = sun still.
As mentioned above, the sun’s movement along your horizon – at sunrise or sunset – is most perceptible around the equinoxes and least perceptible around the solstices. Also, the sun’s daily change of position along the horizon is greater the farther north or south you are from Earth’s equator.
It’s all about your latitude
For example, at around 40 degrees north latitude (Denver, Colorado; island of Sardinia, Italy; Beijing, China), the sun pretty much rises due east and sets due west on the day of the March 20 equinox. Two weeks later, on April 4, the sun rises about 7 degrees north of due east and sets about 7 degrees north of due west. Because the sun’s diameter equals 1/2 degree, that means the sun has been traveling its own diameter (14 days x 1/2 degree = 7 degrees) northward daily.
At 65 degrees north latitude (Fairbanks, Alaska; Siberia; Iceland), the sun also rises and sets close to due east and due west on the day of the equinox. But two weeks later, on April 4, the sun rises and sets about 14 degrees north of due east and west. So, at this far-northern latitude, the sun moves about one degree (two sun-diameters) along the horizon daily during this two-week period from the spring equinox to April 4.
You can track the position of the sunset (or sunrise) location along the horizon during the different seasons. Image via EarthSky.org.
Bottom line: The amount of the sun’s movement along your horizon – at sunrise or sunset – varies with the time of year and with your latitude. It’s most perceptible around the equinoxes and least around the solstices.
View at EarthSky Community Photos. |Rupesh Sangoi in Mumbai, India, captured separate images of the sunrise, showing the sun’s movement along the horizon, between the June and December solstices and on the equinoxes. Rupesh wrote: “Did this for over a year, at sunrise.” Glorious composite, Rupesh! Thank you.
The sun’s movement from day to day along your horizon – at the sunrise or sunset point – is most noticeable around the equinoxes. And many streets in the U.S. and in other parts of the world are oriented either north-south or east-west. So, just by looking out the doorway of your home, you might be able to watch the progress of the sun as it slides from south to north in the weeks and months following the March equinox.
On the equinox, the sun rises directly in the east and sets directly in the west. You can see it move quickly further north each day afterward. No grid of streets to help you? Try tracking the sun’s progress along the horizon by placing bits of tape on an east- or west-facing window of your home. Or just find a clear spot – a place where you can see the horizon – and stand in the same spot whenever you watch the sunrise or sunset. You’ll notice the sun’s movement with respect to trees and other objects in the foreground.
Just be sure to observe from the exact same location every day. It’s enough to note the sunrise or sunset point every week or 10 days. You’ll easily see the sun’s northward shift between now and the June solstice.
Then track between the solstices
What happens at the solstice? At mid-northern latitudes, there’s a two- to three-week time period where you probably won’t discern any movement of the sun along the horizon. That’s where the word solstice comes from. Solstice = sun still.
As mentioned above, the sun’s movement along your horizon – at sunrise or sunset – is most perceptible around the equinoxes and least perceptible around the solstices. Also, the sun’s daily change of position along the horizon is greater the farther north or south you are from Earth’s equator.
It’s all about your latitude
For example, at around 40 degrees north latitude (Denver, Colorado; island of Sardinia, Italy; Beijing, China), the sun pretty much rises due east and sets due west on the day of the March 20 equinox. Two weeks later, on April 4, the sun rises about 7 degrees north of due east and sets about 7 degrees north of due west. Because the sun’s diameter equals 1/2 degree, that means the sun has been traveling its own diameter (14 days x 1/2 degree = 7 degrees) northward daily.
At 65 degrees north latitude (Fairbanks, Alaska; Siberia; Iceland), the sun also rises and sets close to due east and due west on the day of the equinox. But two weeks later, on April 4, the sun rises and sets about 14 degrees north of due east and west. So, at this far-northern latitude, the sun moves about one degree (two sun-diameters) along the horizon daily during this two-week period from the spring equinox to April 4.
You can track the position of the sunset (or sunrise) location along the horizon during the different seasons. Image via EarthSky.org.
Bottom line: The amount of the sun’s movement along your horizon – at sunrise or sunset – varies with the time of year and with your latitude. It’s most perceptible around the equinoxes and least around the solstices.
A galaxy is a vast island of gas, dust and stars in an ocean of space. Typically, galaxies are millions of light-years apart. Galaxies are the building blocks of our universe. Their distribution isn’t random, as one might suppose. Instead, galaxies reside along unimaginably long filaments across the universe, forming a cosmic web of star cities.
View larger. | Have you ever wondered what a galaxy is or how many galaxies are in the universe? Here’s the Webb telescope’s 1st deep field, released in July 2022. This near-infrared image of the galaxy cluster SMACS 0723 contains thousands of galaxies. High-resolution imaging from Webb – combined with a natural effect known as gravitational lensing – made this finely detailed image possible. Image via NASA/ ESA/ CSA/ STScI. Read more about this image.
A galaxy can contain hundreds of billions of stars and be many thousands of light-years across. Our own galaxy, the Milky Way, is around 100,000 light-years in diameter. That’s about 587,900 trillion miles, or nearly a million trillion kilometers.
The three types of galaxies are spiral, elliptical or irregular.
Galaxy sizes vary widely, ranging from very small to unbelievably enormous. Small dwarf galaxies contain about 100 million stars. Giant galaxies contain more than a trillion stars.
Also, there are an estimated two hundred billion galaxies in the universe.
Here is a closeup view of 1 small portion of a Webb image that shows more than 45,000 galaxies. Image via NASA/ ESA/ CSA/ Brant Robertson (UC Santa Cruz)/ Ben Johnson (CfA)/ Sandro Tacchella (Cambridge)/ Marcia Rieke (University of Arizona)/ Daniel Eisenstein (CfA)/ Alyssa Pagan (STScI).
The discovery of other galaxies
The famous astronomer Edwin P. Hubble first classified galaxies based on their visual appearance in the late 1920s and 30s. In fact, Hubble’s classification of galaxies remains in use today. Of course, since Hubble’s time, like any effective classification system, it has evolved from ongoing observations. Hubble identified several basic types of galaxies, each containing subtypes.
— Royal Astronomical Society (@RoyalAstroSoc) June 11, 2019
Before Hubble’s study of galaxies, we believed that our galaxy was the only one in the universe. Astronomers thought that the smudges of light they saw through their telescopes were in fact nebulae within our own galaxy. However, Hubble discovered that these nebulae were galaxies. Additionally, it was Hubble who demonstrated, by measuring their velocities, that they lie at vast distances from us.
Galaxies are light-years away
These galaxies lie millions of light-years beyond the Milky Way. The distances are so huge these galaxies appear tiny in all but the largest telescopes. Moreover, Hubble demonstrated that, wherever he looked, galaxies were receding from us in all directions. And the farther away they are, the faster they are receding. Thus, Hubble had discovered that the universe is expanding.
View at EarthSky Community Photos. | Harshwardhan Pathak of India, using a large remote telescope in Chile, captured the galaxy NGC 1232 in the constellation Eridanus on February 1, 2024. Harshwardhan wrote: “NGC 1232, also known as the Eye of God Galaxy, is an intermediate spiral galaxy about 60 million light-years away. German-British astronomer William Herschel discovered it on October 20, 1784.” Thank you, Harshwardhan!
Spiral galaxies
The most common type of galaxy is a spiral galaxy. The Milky Way is a spiral galaxy. Spiral galaxies have majestic, sweeping arms, thousands of light-years long. They contain millions upon millions of stars. Their spiral arms stand out because of bright stars, glowing gas and dust. Spiral galaxies are active with star formation.
Also, spiral galaxies have a bright center, made up of a dense concentration of stars. There are so many stars that from a distance the galaxy’s center looks like a solid ball. This ball of stars is known as the galactic bulge.
Also, there are two types of spiral galaxies. There are regular spirals and barred spirals. If the spiral has bars, they extend off the central bulge. Then, the spiral arms start at the end of the bar. In fact, the Milky Way Galaxy is a barred spiral galaxy.
The 3 most common types of galaxies. The top row shows schematic illustrations, and the bottom row shows actual images of galaxies that fit each of the 3 categories. Image via A. Feild/ STScI/ Hubblesite.
Elliptical and irregular galaxies
Elliptical galaxies are the universe’s largest galaxies. In fact, giant elliptical galaxies can be about 300,000 light-years across. But dwarf elliptical galaxies – the most common elliptical – are only a few thousand light-years across. There are several shapes of elliptical galaxies, ranging from circular to football-shaped.
Overall, 1/3 of all galaxies are elliptical galaxies. Elliptical galaxies contain very little gas and dust compared to a spiral or irregular galaxy. They are no longer actively forming stars. The stars in elliptical galaxies are older stars and contain very few heavier elements.
Irregular-shaped galaxies have all sorts of different shapes but they don’t look like a spiral or elliptical galaxy.
Irregular galaxies can have very little dust or a lot. Plus, they can show active star-forming regions or have little-to-no star formation occurring. They seemed plentiful in the early universe.
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).
Our Milky Way Galaxy
The Milky Way, in fact, falls into one of Hubble’s spiral galaxy sub-types. It’s a barred spiral, which means it has a bar of stars protruding out from each side of its center. As the spiral arms sweep out in their graceful and enormous arcs, the ends of the bars are the anchors. This is a recent discovery and it’s unknown how bars form in a galaxy. Our solar system is situated about 2/3 of the way out from the galactic center toward the periphery of the galaxy, embedded in one of these spiral arms.
Another recent discovery is that the disk of the Milky Way is warped, like a long-playing vinyl record left too long in the sun. Exactly why is unknown, but it may be the result of a gravitational encounter with another galaxy early in the Milky Way’s history.
It also appears that all galaxies rotate. For example, the Milky Way takes 226 million years to spin around once. Since its creation, the Earth has traveled 20 times around the galaxy.
Galaxies come in clusters
Galaxies group together in clusters. Our own galaxy is part of what is called the Local Group, and it contains at least 80 galaxies. The three large galaxies in the Local Group are the Andromeda Galaxy, the Milky Way Galaxy and the Triangulum Galaxy. The rest of the galaxies in our local group are dwarf galaxies.
The “glue” that binds stars into galaxies, galaxies into clusters, clusters into superclusters and superclusters into filaments is – of course – gravity. In fact, gravity is the universe’s construction worker, which sculpts all the structures we see in the cosmos.
The Universe is Infinite. However our existence in our current Galaxy Cluster is Finite. Time is also a factor… Our Galaxy Clusters actually expand into the void of space over time. pic.twitter.com/EAOcisPdZn
Most galaxies are flying apart from each other. But those astronomically close to each other will be gravitationally bound to each other. Caught in an inexorable gravitational dance, eventually they merge, passing through each other over millions of years. They eventually form a single, amorphous elliptical galaxy. Gravity shockwaves compress huge clouds of interstellar gas and dust during such mergers, giving rise to new generations of stars.
The Milky Way is caught in such a gravitational embrace with M31, aka the Andromeda Galaxy, which is 2 1/2 million light-years distant. Both galaxies are moving toward each other because of gravitational attraction: they will merge in about 6 billion years. However, huge halos of gas surround both galaxies and may extend for millions of light-years. And it was discovered that the halos of the Milky Way and M31 have already started to touch.
Galaxy mergers and companion galaxies
Galaxy mergers are common. The universe is full of examples of galaxies in various stages of merging together, their structures disrupted and distorted by gravity, forming bizarre and beautiful shapes.
Galaxies may take billions of years to fully merge into a single galaxy. As astronomers look outward in space, they can only see glimpses of this long merger process. Located 300 million light-years away in the constellation Coma Berenices, these 2 colliding galaxies have been nicknamed the Mice Galaxies because of the long tails of stars and gas emanating from each galaxy. Otherwise known as NGC 4676, the pair will eventually merge into a single giant galaxy. Image via NASA/ ESA/ Wikimedia Commons (public domain).
Then, at the lower end of the galactic size scale, there are so-called dwarf galaxies. They consist of a few hundred to up to several billion stars. Their origin is not clear. Typically, they have no clearly defined structure. Astronomers believe they were born in the same way as larger galaxies like the Milky Way, but for whatever reason they stopped growing. Ensnared by the gravity of a larger galaxy, they orbit its periphery. The Milky Way has around 60 dwarf galaxies orbiting it that we know of, although some models predict there should be many more.
The two most famous dwarf galaxies for us earthlings are, of course, the Large and Small Magellanic Clouds, visible to the unaided eye in Earth’s Southern Hemisphere sky.
Eventually, these and other dwarf galaxies will rip apart under the titanic pull of the Milky Way’s gravity. This will leave behind a barely noticeable stream of stars across the sky, slowly dissipating over eons.
The Large Magellanic Cloud spills across the border of Dorado and Mensa. The Small Magellanic Cloud is at lower left. Image via Yuri Beletsky/ LCO/ ESO.
Supermassive black holes lurk in galaxy centers
At the center of most galaxies lurks a supermassive black hole, of millions or even billions of solar masses. For example, TON 618, has a mass 66 billion times that of our sun. The one at the center of our own Milky Way galaxy possesses 4.6 million solar masses.
The origin and evolution of supermassive black holes remains a mystery. A few years ago, astronomers uncovered a surprising fact: in spiral galaxies, the mass of the supermassive black hole has a direct linear relationship with the mass of the galactic bulge. The more mass the black hole has, the more stars there are in the bulge. No one knows exactly what the significance of this relationship may be. However, its existence seems to indicate that the growth of a galaxy’s stellar population is linked to that of its supermassive black hole.
This discovery comes at a time when astronomers are beginning to realize that a supermassive black hole may control the fate of its host galaxy. The copious amount of electromagnetic radiation emitted from the maelstrom of material orbiting the central black hole. This is known as the accretion disk, and the radiation may push away and dissipate the clouds of interstellar hydrogen from which new stars form. This acts as an inhibitor on the galaxy’s ability to give birth to new stars. Ultimately, the activity of supermassive black holes may link to the emergence of life itself. This is an area that is undergoing extensive research.
While astronomers still know very little about exactly how galaxies formed in the first place – we see them in their nascent state only a few hundred million years after the Big Bang – the study of galaxies is an endless voyage of discovery.
We discovered other galaxies exist about a century ago
Around a hundred years ago we realized that other galaxies exist besides our own. Since then, we have learned so much about these grand, majestic star cities. And there is still much to learn.
Some galaxies from our EarthSky Community Photos
View at EarthSky Community Photos. | Shaurya Salunkhe in Velhe, Maharashtra, India, used a telephoto lens to capture this view of Messier 31, the Andromeda Galaxy, on January 11, 2026. Shaurya wrote: “I captured the Andromeda Galaxy, the Milky Way’s closest neighbor and the largest galaxy of the Local Group. This is the farthest object that is visible to the unaided eye. It’s 3 times larger than the Milky Way and is approximately 2.5 million light-years away. It is a fascinating target with stunning colours not to mention the bonus little galaxies (M32 and M110) near it.” Thank you, Shaurya!View at EarthSky Community Photos. | Andy Dungan near Cotopaxi, Colorado, captured this view of spiral galaxy IC 342, in the constellation Camelopardalis (also known as Caldwell 5), on June 22, 2025. Andy wrote: “This is really sort of the first of the winter galaxies. The challenge for taking pics of this galaxy is how dim it is compare to many others of its size. Evidently there is a substantial amount of dust someplace in between here and the 7-10 million light-years to the galaxy. As I said above more exposure and using PixInsight made a substantial difference in the quality of the pic. Ya, progress!!” Thank you, Andy!View at EarthSky Community Photos. | EarthSky’s own Marcy Curran in Cheyenne, Wyoming, captured the Pinwheel Galaxy on July 1, 2025. Marcy wrote: “The Pinwheel Galaxy (M101) is a face-on, counterclockwise intermediate spiral galaxy. It’s 21 million light-years from Earth in the constellation Ursa Major. It has a diameter of approximately 252,000 light-years and contains around one trillion stars. Pierre Méchain discovered it in 1781. Then Charles Messier verified its position before adding it to his Messier Catalog. It was 101 out of 110 deep-sky objects. The beautiful Pinwheel Galaxy is a near-perfect representation of a spiral galaxy.” Thank you, Marcy!
Bottom line: A galaxy is a vast island of gas, dust and stars in an ocean of space. There are three types of galaxies. Learn about these starry islands in space.
A galaxy is a vast island of gas, dust and stars in an ocean of space. Typically, galaxies are millions of light-years apart. Galaxies are the building blocks of our universe. Their distribution isn’t random, as one might suppose. Instead, galaxies reside along unimaginably long filaments across the universe, forming a cosmic web of star cities.
View larger. | Have you ever wondered what a galaxy is or how many galaxies are in the universe? Here’s the Webb telescope’s 1st deep field, released in July 2022. This near-infrared image of the galaxy cluster SMACS 0723 contains thousands of galaxies. High-resolution imaging from Webb – combined with a natural effect known as gravitational lensing – made this finely detailed image possible. Image via NASA/ ESA/ CSA/ STScI. Read more about this image.
A galaxy can contain hundreds of billions of stars and be many thousands of light-years across. Our own galaxy, the Milky Way, is around 100,000 light-years in diameter. That’s about 587,900 trillion miles, or nearly a million trillion kilometers.
The three types of galaxies are spiral, elliptical or irregular.
Galaxy sizes vary widely, ranging from very small to unbelievably enormous. Small dwarf galaxies contain about 100 million stars. Giant galaxies contain more than a trillion stars.
Also, there are an estimated two hundred billion galaxies in the universe.
Here is a closeup view of 1 small portion of a Webb image that shows more than 45,000 galaxies. Image via NASA/ ESA/ CSA/ Brant Robertson (UC Santa Cruz)/ Ben Johnson (CfA)/ Sandro Tacchella (Cambridge)/ Marcia Rieke (University of Arizona)/ Daniel Eisenstein (CfA)/ Alyssa Pagan (STScI).
The discovery of other galaxies
The famous astronomer Edwin P. Hubble first classified galaxies based on their visual appearance in the late 1920s and 30s. In fact, Hubble’s classification of galaxies remains in use today. Of course, since Hubble’s time, like any effective classification system, it has evolved from ongoing observations. Hubble identified several basic types of galaxies, each containing subtypes.
— Royal Astronomical Society (@RoyalAstroSoc) June 11, 2019
Before Hubble’s study of galaxies, we believed that our galaxy was the only one in the universe. Astronomers thought that the smudges of light they saw through their telescopes were in fact nebulae within our own galaxy. However, Hubble discovered that these nebulae were galaxies. Additionally, it was Hubble who demonstrated, by measuring their velocities, that they lie at vast distances from us.
Galaxies are light-years away
These galaxies lie millions of light-years beyond the Milky Way. The distances are so huge these galaxies appear tiny in all but the largest telescopes. Moreover, Hubble demonstrated that, wherever he looked, galaxies were receding from us in all directions. And the farther away they are, the faster they are receding. Thus, Hubble had discovered that the universe is expanding.
View at EarthSky Community Photos. | Harshwardhan Pathak of India, using a large remote telescope in Chile, captured the galaxy NGC 1232 in the constellation Eridanus on February 1, 2024. Harshwardhan wrote: “NGC 1232, also known as the Eye of God Galaxy, is an intermediate spiral galaxy about 60 million light-years away. German-British astronomer William Herschel discovered it on October 20, 1784.” Thank you, Harshwardhan!
Spiral galaxies
The most common type of galaxy is a spiral galaxy. The Milky Way is a spiral galaxy. Spiral galaxies have majestic, sweeping arms, thousands of light-years long. They contain millions upon millions of stars. Their spiral arms stand out because of bright stars, glowing gas and dust. Spiral galaxies are active with star formation.
Also, spiral galaxies have a bright center, made up of a dense concentration of stars. There are so many stars that from a distance the galaxy’s center looks like a solid ball. This ball of stars is known as the galactic bulge.
Also, there are two types of spiral galaxies. There are regular spirals and barred spirals. If the spiral has bars, they extend off the central bulge. Then, the spiral arms start at the end of the bar. In fact, the Milky Way Galaxy is a barred spiral galaxy.
The 3 most common types of galaxies. The top row shows schematic illustrations, and the bottom row shows actual images of galaxies that fit each of the 3 categories. Image via A. Feild/ STScI/ Hubblesite.
Elliptical and irregular galaxies
Elliptical galaxies are the universe’s largest galaxies. In fact, giant elliptical galaxies can be about 300,000 light-years across. But dwarf elliptical galaxies – the most common elliptical – are only a few thousand light-years across. There are several shapes of elliptical galaxies, ranging from circular to football-shaped.
Overall, 1/3 of all galaxies are elliptical galaxies. Elliptical galaxies contain very little gas and dust compared to a spiral or irregular galaxy. They are no longer actively forming stars. The stars in elliptical galaxies are older stars and contain very few heavier elements.
Irregular-shaped galaxies have all sorts of different shapes but they don’t look like a spiral or elliptical galaxy.
Irregular galaxies can have very little dust or a lot. Plus, they can show active star-forming regions or have little-to-no star formation occurring. They seemed plentiful in the early universe.
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).
Our Milky Way Galaxy
The Milky Way, in fact, falls into one of Hubble’s spiral galaxy sub-types. It’s a barred spiral, which means it has a bar of stars protruding out from each side of its center. As the spiral arms sweep out in their graceful and enormous arcs, the ends of the bars are the anchors. This is a recent discovery and it’s unknown how bars form in a galaxy. Our solar system is situated about 2/3 of the way out from the galactic center toward the periphery of the galaxy, embedded in one of these spiral arms.
Another recent discovery is that the disk of the Milky Way is warped, like a long-playing vinyl record left too long in the sun. Exactly why is unknown, but it may be the result of a gravitational encounter with another galaxy early in the Milky Way’s history.
It also appears that all galaxies rotate. For example, the Milky Way takes 226 million years to spin around once. Since its creation, the Earth has traveled 20 times around the galaxy.
Galaxies come in clusters
Galaxies group together in clusters. Our own galaxy is part of what is called the Local Group, and it contains at least 80 galaxies. The three large galaxies in the Local Group are the Andromeda Galaxy, the Milky Way Galaxy and the Triangulum Galaxy. The rest of the galaxies in our local group are dwarf galaxies.
The “glue” that binds stars into galaxies, galaxies into clusters, clusters into superclusters and superclusters into filaments is – of course – gravity. In fact, gravity is the universe’s construction worker, which sculpts all the structures we see in the cosmos.
The Universe is Infinite. However our existence in our current Galaxy Cluster is Finite. Time is also a factor… Our Galaxy Clusters actually expand into the void of space over time. pic.twitter.com/EAOcisPdZn
Most galaxies are flying apart from each other. But those astronomically close to each other will be gravitationally bound to each other. Caught in an inexorable gravitational dance, eventually they merge, passing through each other over millions of years. They eventually form a single, amorphous elliptical galaxy. Gravity shockwaves compress huge clouds of interstellar gas and dust during such mergers, giving rise to new generations of stars.
The Milky Way is caught in such a gravitational embrace with M31, aka the Andromeda Galaxy, which is 2 1/2 million light-years distant. Both galaxies are moving toward each other because of gravitational attraction: they will merge in about 6 billion years. However, huge halos of gas surround both galaxies and may extend for millions of light-years. And it was discovered that the halos of the Milky Way and M31 have already started to touch.
Galaxy mergers and companion galaxies
Galaxy mergers are common. The universe is full of examples of galaxies in various stages of merging together, their structures disrupted and distorted by gravity, forming bizarre and beautiful shapes.
Galaxies may take billions of years to fully merge into a single galaxy. As astronomers look outward in space, they can only see glimpses of this long merger process. Located 300 million light-years away in the constellation Coma Berenices, these 2 colliding galaxies have been nicknamed the Mice Galaxies because of the long tails of stars and gas emanating from each galaxy. Otherwise known as NGC 4676, the pair will eventually merge into a single giant galaxy. Image via NASA/ ESA/ Wikimedia Commons (public domain).
Then, at the lower end of the galactic size scale, there are so-called dwarf galaxies. They consist of a few hundred to up to several billion stars. Their origin is not clear. Typically, they have no clearly defined structure. Astronomers believe they were born in the same way as larger galaxies like the Milky Way, but for whatever reason they stopped growing. Ensnared by the gravity of a larger galaxy, they orbit its periphery. The Milky Way has around 60 dwarf galaxies orbiting it that we know of, although some models predict there should be many more.
The two most famous dwarf galaxies for us earthlings are, of course, the Large and Small Magellanic Clouds, visible to the unaided eye in Earth’s Southern Hemisphere sky.
Eventually, these and other dwarf galaxies will rip apart under the titanic pull of the Milky Way’s gravity. This will leave behind a barely noticeable stream of stars across the sky, slowly dissipating over eons.
The Large Magellanic Cloud spills across the border of Dorado and Mensa. The Small Magellanic Cloud is at lower left. Image via Yuri Beletsky/ LCO/ ESO.
Supermassive black holes lurk in galaxy centers
At the center of most galaxies lurks a supermassive black hole, of millions or even billions of solar masses. For example, TON 618, has a mass 66 billion times that of our sun. The one at the center of our own Milky Way galaxy possesses 4.6 million solar masses.
The origin and evolution of supermassive black holes remains a mystery. A few years ago, astronomers uncovered a surprising fact: in spiral galaxies, the mass of the supermassive black hole has a direct linear relationship with the mass of the galactic bulge. The more mass the black hole has, the more stars there are in the bulge. No one knows exactly what the significance of this relationship may be. However, its existence seems to indicate that the growth of a galaxy’s stellar population is linked to that of its supermassive black hole.
This discovery comes at a time when astronomers are beginning to realize that a supermassive black hole may control the fate of its host galaxy. The copious amount of electromagnetic radiation emitted from the maelstrom of material orbiting the central black hole. This is known as the accretion disk, and the radiation may push away and dissipate the clouds of interstellar hydrogen from which new stars form. This acts as an inhibitor on the galaxy’s ability to give birth to new stars. Ultimately, the activity of supermassive black holes may link to the emergence of life itself. This is an area that is undergoing extensive research.
While astronomers still know very little about exactly how galaxies formed in the first place – we see them in their nascent state only a few hundred million years after the Big Bang – the study of galaxies is an endless voyage of discovery.
We discovered other galaxies exist about a century ago
Around a hundred years ago we realized that other galaxies exist besides our own. Since then, we have learned so much about these grand, majestic star cities. And there is still much to learn.
Some galaxies from our EarthSky Community Photos
View at EarthSky Community Photos. | Shaurya Salunkhe in Velhe, Maharashtra, India, used a telephoto lens to capture this view of Messier 31, the Andromeda Galaxy, on January 11, 2026. Shaurya wrote: “I captured the Andromeda Galaxy, the Milky Way’s closest neighbor and the largest galaxy of the Local Group. This is the farthest object that is visible to the unaided eye. It’s 3 times larger than the Milky Way and is approximately 2.5 million light-years away. It is a fascinating target with stunning colours not to mention the bonus little galaxies (M32 and M110) near it.” Thank you, Shaurya!View at EarthSky Community Photos. | Andy Dungan near Cotopaxi, Colorado, captured this view of spiral galaxy IC 342, in the constellation Camelopardalis (also known as Caldwell 5), on June 22, 2025. Andy wrote: “This is really sort of the first of the winter galaxies. The challenge for taking pics of this galaxy is how dim it is compare to many others of its size. Evidently there is a substantial amount of dust someplace in between here and the 7-10 million light-years to the galaxy. As I said above more exposure and using PixInsight made a substantial difference in the quality of the pic. Ya, progress!!” Thank you, Andy!View at EarthSky Community Photos. | EarthSky’s own Marcy Curran in Cheyenne, Wyoming, captured the Pinwheel Galaxy on July 1, 2025. Marcy wrote: “The Pinwheel Galaxy (M101) is a face-on, counterclockwise intermediate spiral galaxy. It’s 21 million light-years from Earth in the constellation Ursa Major. It has a diameter of approximately 252,000 light-years and contains around one trillion stars. Pierre Méchain discovered it in 1781. Then Charles Messier verified its position before adding it to his Messier Catalog. It was 101 out of 110 deep-sky objects. The beautiful Pinwheel Galaxy is a near-perfect representation of a spiral galaxy.” Thank you, Marcy!
Bottom line: A galaxy is a vast island of gas, dust and stars in an ocean of space. There are three types of galaxies. Learn about these starry islands in space.
Artist’s concept of a collision of 2 exoplanets. Light from the collision in a star system called Gaia20ehk could be seen in the year 2021. Image via Anastasios Tzanidakis/ University of Washington.
A grad student was looking through old data when he spied something unusual.
The data revealed the collision of 2 exoplanets, 11,000 light-years away.
Astronomers hope to detect about 100 similar collisions in the coming decade, using the new Rubin Observatory in Chile. It’s important because this collision might be similar to the one that formed Earth’s moon. And Earth’s moon is key to life.
An astronomy grad student at the University of Washington – Anastasios Tzanidakis – was looking through old telescope data when he noticed something odd. It was a seemingly ordinary star, called Gaia20ehk, flickering wildly in brightness. Intrigued, he and his colleagues investigated further. And they determined that the flickering was due to large amounts of hot dust and rocks passing in front of the star. They concluded the flickering of the star must indicate a catastrophic collision between two of its planets, 11,000 light-years away.
The star’s light output was nice and flat. But, starting in 2016, it had these three dips in brightness. And then, right around 2021, it went completely bonkers. I can’t emphasize enough that stars like our sun don’t do that. So, when we saw this one, we were like ‘Hello, what’s going on here?’
It’s incredible that various telescopes caught this impact just as the light of the collision reached Earth. There are only a few other planetary collisions of any kind on record, and none that bear so many similarities to the impact that created the Earth and moon.
If we can observe more moments like this elsewhere in the galaxy, it will teach us lots about the formation of our world.
Stars form from rotating disks of gas and dust. Afterwards, there’s a leftover disk of material called a protoplanetary disk. And at first this disk contains just dust, gas, ice and rocks. But, over millions of years, the materials in the disk coalesce, under gravitational forces. So planets and other small bodies, such as asteroids and comets, form out of the disk.
Conditions with the disk of an early stellar system can be chaotic. Planets can collide and shatter. Or the force of an impact could hurl a planet out of its stellar system. But eventually, over a timescale of 100 million years or so, the new-born solar system settles into a stable state.
Collisions between newly formed extrasolar planets are likely quite common. But catching one in the act is hard. That’s because – in a scenario like the one detected by Anastasios Tzanidakis and colleagues – telescopes can detect the flickering starlight only if the orbiting collision debris is in the line of sight between us and the star.
Star system Gaia20ehk
The star system Gaia20ehk is about 11,000 light-years from Earth. It’s near the direction of the constellation Puppis the Stern. It’s in a stable phase of its evolution, known as the main sequence phase. That means the star is steadily burning hydrogen to helium in its core.
Gaia20ehk is at the center of this image. A small region of the field is shown in the inset box with the star marked by orange crosshairs. It’s about 11,000 light-years from Earth, near the direction of the constellation Pupis the Stern. Image via NASA/NSF NOIRLab/ University of Washington.
Looking in both visible and infrared
For a long time, as viewed through earthly telescopes, Gaia20ehk shone with a steady light. But starting in 2016, Tzanidakis said, there were three dips in its brightness. Then, in 2021, the star’s brightness became erratic.
Davenport suggested they examine this star at infrared wavelengths. And the results were a revelation. Tzanidakis commented:
The infrared light curve was the complete opposite of the visible light. As the visible light began to flicker and dim, the infrared light spiked. Which could mean that the material blocking the star is hot — so hot that it’s glowing in the infrared.
But what caused the dips in light before 2021? Tzanidakis said:
That could be caused by the two planets spiraling closer and closer to each other. At first, they had a series of grazing impacts, which wouldn’t produce a lot of infrared energy. Then, they had their big catastrophic collision, and the infrared really ramped up.
The plot at the top shows Gaia20ehk’s brightness in visible light. There were 3 small dips that were followed, in 2021, by a chaotic variation in brightness. Meanwhile, the bottom plot shows brightness in infrared wavelengths for the same time period. Note that the infrared brightness increased significantly when the visible light brightness was chaotic. Image via Tzanidakis et al./ The Astrophysical Journal Letters/ University of Washington.
Could a similar collision have created our moon?
Some scientists think that a similar collision might have created our moon. They say that about 4.5 billion years ago, an object the size of Mars collided into Earth, ripping out material from our young planet to form the moon.
Gaia20ehk is only slightly more massive than our sun. In addition, the orbiting material causing the star’s fluctuating brightness is about one astronomical unit from the star. So whatever happened in this system to create the debris is located in this star system at about the same distance between our sun and Earth-moon system.
The researchers think the hot debris could, at that distance, eventually cool down enough to create a system similar to our Earth and moon. But they won’t know for sure until the dust literally settles, which could take a few million years.
This is a simulation, from 2022, of how the moon may have formed. A body the size of Mars crashed into Earth, early in its formation, ripping out material that eventually became the moon. Simulation via NASA/ Durham University/ Jacob Kegerreis.
Finding more systems with collisions
In the meantime, the Vera C. Rubin Observatory is making periodic scans of the southern hemisphere sky. If something changes in the sky – a supernova, a new comet, a star changing in brightness – astronomers want to be alerted. They want to study what’s going on in real time.
Davenport thinks that Rubin could find as many as 100 collisions in the coming 10 years. If so, observing these events could help astronomers understand the processes that create Earth–moon-like systems, which in turn could inform the search for habitable exoplanets. Davenport commented:
How rare is the event that created the Earth and moon? That question is fundamental to astrobiology. It seems like the moon is one of the magical ingredients that makes the Earth a good place for life. It can help shield Earth from some asteroids. It produces ocean tides and weather that allow chemistry and biology to mix globally. And it might even play a role in driving tectonic plate activity.
Right now, we don’t know how common these dynamics are. But if we catch more of these collisions, we’ll start to figure it out.
Bottom line: Astronomers found that the erratically flickering light from a stable star was due to debris from the collision of two exoplanets.
Artist’s concept of a collision of 2 exoplanets. Light from the collision in a star system called Gaia20ehk could be seen in the year 2021. Image via Anastasios Tzanidakis/ University of Washington.
A grad student was looking through old data when he spied something unusual.
The data revealed the collision of 2 exoplanets, 11,000 light-years away.
Astronomers hope to detect about 100 similar collisions in the coming decade, using the new Rubin Observatory in Chile. It’s important because this collision might be similar to the one that formed Earth’s moon. And Earth’s moon is key to life.
An astronomy grad student at the University of Washington – Anastasios Tzanidakis – was looking through old telescope data when he noticed something odd. It was a seemingly ordinary star, called Gaia20ehk, flickering wildly in brightness. Intrigued, he and his colleagues investigated further. And they determined that the flickering was due to large amounts of hot dust and rocks passing in front of the star. They concluded the flickering of the star must indicate a catastrophic collision between two of its planets, 11,000 light-years away.
The star’s light output was nice and flat. But, starting in 2016, it had these three dips in brightness. And then, right around 2021, it went completely bonkers. I can’t emphasize enough that stars like our sun don’t do that. So, when we saw this one, we were like ‘Hello, what’s going on here?’
It’s incredible that various telescopes caught this impact just as the light of the collision reached Earth. There are only a few other planetary collisions of any kind on record, and none that bear so many similarities to the impact that created the Earth and moon.
If we can observe more moments like this elsewhere in the galaxy, it will teach us lots about the formation of our world.
Stars form from rotating disks of gas and dust. Afterwards, there’s a leftover disk of material called a protoplanetary disk. And at first this disk contains just dust, gas, ice and rocks. But, over millions of years, the materials in the disk coalesce, under gravitational forces. So planets and other small bodies, such as asteroids and comets, form out of the disk.
Conditions with the disk of an early stellar system can be chaotic. Planets can collide and shatter. Or the force of an impact could hurl a planet out of its stellar system. But eventually, over a timescale of 100 million years or so, the new-born solar system settles into a stable state.
Collisions between newly formed extrasolar planets are likely quite common. But catching one in the act is hard. That’s because – in a scenario like the one detected by Anastasios Tzanidakis and colleagues – telescopes can detect the flickering starlight only if the orbiting collision debris is in the line of sight between us and the star.
Star system Gaia20ehk
The star system Gaia20ehk is about 11,000 light-years from Earth. It’s near the direction of the constellation Puppis the Stern. It’s in a stable phase of its evolution, known as the main sequence phase. That means the star is steadily burning hydrogen to helium in its core.
Gaia20ehk is at the center of this image. A small region of the field is shown in the inset box with the star marked by orange crosshairs. It’s about 11,000 light-years from Earth, near the direction of the constellation Pupis the Stern. Image via NASA/NSF NOIRLab/ University of Washington.
Looking in both visible and infrared
For a long time, as viewed through earthly telescopes, Gaia20ehk shone with a steady light. But starting in 2016, Tzanidakis said, there were three dips in its brightness. Then, in 2021, the star’s brightness became erratic.
Davenport suggested they examine this star at infrared wavelengths. And the results were a revelation. Tzanidakis commented:
The infrared light curve was the complete opposite of the visible light. As the visible light began to flicker and dim, the infrared light spiked. Which could mean that the material blocking the star is hot — so hot that it’s glowing in the infrared.
But what caused the dips in light before 2021? Tzanidakis said:
That could be caused by the two planets spiraling closer and closer to each other. At first, they had a series of grazing impacts, which wouldn’t produce a lot of infrared energy. Then, they had their big catastrophic collision, and the infrared really ramped up.
The plot at the top shows Gaia20ehk’s brightness in visible light. There were 3 small dips that were followed, in 2021, by a chaotic variation in brightness. Meanwhile, the bottom plot shows brightness in infrared wavelengths for the same time period. Note that the infrared brightness increased significantly when the visible light brightness was chaotic. Image via Tzanidakis et al./ The Astrophysical Journal Letters/ University of Washington.
Could a similar collision have created our moon?
Some scientists think that a similar collision might have created our moon. They say that about 4.5 billion years ago, an object the size of Mars collided into Earth, ripping out material from our young planet to form the moon.
Gaia20ehk is only slightly more massive than our sun. In addition, the orbiting material causing the star’s fluctuating brightness is about one astronomical unit from the star. So whatever happened in this system to create the debris is located in this star system at about the same distance between our sun and Earth-moon system.
The researchers think the hot debris could, at that distance, eventually cool down enough to create a system similar to our Earth and moon. But they won’t know for sure until the dust literally settles, which could take a few million years.
This is a simulation, from 2022, of how the moon may have formed. A body the size of Mars crashed into Earth, early in its formation, ripping out material that eventually became the moon. Simulation via NASA/ Durham University/ Jacob Kegerreis.
Finding more systems with collisions
In the meantime, the Vera C. Rubin Observatory is making periodic scans of the southern hemisphere sky. If something changes in the sky – a supernova, a new comet, a star changing in brightness – astronomers want to be alerted. They want to study what’s going on in real time.
Davenport thinks that Rubin could find as many as 100 collisions in the coming 10 years. If so, observing these events could help astronomers understand the processes that create Earth–moon-like systems, which in turn could inform the search for habitable exoplanets. Davenport commented:
How rare is the event that created the Earth and moon? That question is fundamental to astrobiology. It seems like the moon is one of the magical ingredients that makes the Earth a good place for life. It can help shield Earth from some asteroids. It produces ocean tides and weather that allow chemistry and biology to mix globally. And it might even play a role in driving tectonic plate activity.
Right now, we don’t know how common these dynamics are. But if we catch more of these collisions, we’ll start to figure it out.
Bottom line: Astronomers found that the erratically flickering light from a stable star was due to debris from the collision of two exoplanets.
We tell you all you need to know about halos in our YouTube video here. Don’t forget to subscribe!
What causes halos?
Have you ever looked up and spotted a large ring of light around the sun or moon? Scientists refer to these as 22-degree halos. They got that name because the radius of the circle is always approximately 22 degrees.
There’s an old weather saying: ring around the moon means rain soon. There’s truth to this saying, because high cirrus clouds often come before a storm. Notice in these photos that the sky looks fairly clear. After all, you can see the sun or moon. And yet halos are a sign of high, thin cirrus clouds drifting 20,000 feet (6 km) or more above our heads.
These clouds contain millions of tiny ice crystals. The halos you see are caused by both refraction, or splitting of light, and also by reflection, or glints of light from these ice crystals. The crystals must be oriented and positioned just so with respect to your eye, for the halo to appear.
That’s why, like rainbows, halos around the sun – or moon – are personal. Everyone sees their own unique halo, made by the ice crystals from their point of view. So they are different from the ice crystals making the halo of a person standing next to you.
View at EarthSky Community Photos. | Roberto Ortu captured this moon halo on February 2, 2026, in Italy and wrote: “A moon halo has an apparent radius of 22 degrees and forms around the moon due to refraction by hexagonal-shaped ice crystals that are present in Earth’s atmosphere.” Thank you, Roberto! Notice that – unlike solar halos, which can be colorful – lunar halos are mostly colorless.
A word of caution for photographers
Take care when photographing solar halos. Pointing a camera directly at the unobscured sun can damage it. Never look directly at the sun, even when it is less bright through clouds or fog.
Are halos more common at high latitudes?
We asked Les Cowley of the website Atmospheric Optics if halos around the sun and moon are more frequently seen at high latitudes and less commonly seen closer to the equator. He said:
That’s a good question that is not easy to answer accurately because no halo frequency statistics are collected except in one or two mid-latitude European countries.
We need to distinguish between (a) halos formed by low level diamond dust during very cold weather and (b) halos formed by ice crystals in high cirrus cloud.
Obviously (a) halos only occur in polar regions or countries with very cold winters (Canada for example is not high latitude).
(b) Halos can occur anywhere on the planet during winter or summer. Their frequency depends on the frequency of cirrus coverage and whether it has had a history such that it contains halo forming crystals. The latter is hard to predict. For example, there are major differences in halo frequencies and types of halos across even 200 miles [300 km] in the U.K.
Halos are made by both refraction and reflection ice crystals, such as these, in this photo by Walt Tate. Image via Walt Tate/ Atmospheric Optics. Used with permission.
If you see a halo, notice this!
Because moonlight isn’t very bright, lunar halos are mostly colorless. However, you might notice red on the inside and blue on the outside of the halo. These colors are more noticeable in halos around the sun. If you do see a halo around the moon or sun, notice that the inner edge is sharp, while the outer edge is more diffuse. Also, notice that the sky surrounding the halo is darker than the rest of the sky.
Halo photos from EarthSky’s Community
View at EarthSky Community Photos. | Samit Saha captured this image on January 30, 2026, and wrote: “A bright lunar halo surrounds the moon on a bone-chilling winter night in India. The circular ring formed as moonlight passed through countless hexagonal ice crystals suspended in high, thin cirrostratus clouds, creating the classic 22-degree halo. Snow-covered hills beneath the sky emphasize the clarity and depth of the winter atmosphere. The wide-field view reveals several familiar constellations – Orion, Taurus, Gemini, and the Pleiades – along with the bright planet Jupiter, all sharing the frame with the glowing halo. Such halos often signal approaching weather changes, yet for a brief moment, the sky offered a rare balance of atmospheric optics and celestial geometry, captured in a single exposure.” Thank you, Samit!View at EarthSky Community Photos. | Bonnie Swan captured this image in Wisconsin on January 21, 2026, and wrote: “While driving east early in the morning, the halo and sun dogs around the rising sun continued to be very bright, when I found a vantage point to get the whole image, I had to pull over to capture it!” Thank you, Bonnie!View at EarthSky Community Photos. | Dario Giannobile captured this in Manhattan on December 12, 2025, and wrote: “In a handheld shot of the Statue of Liberty taken from the ferry connecting Ellis Island to Manhattan, with seagulls crossing the sky, a series of rare optical phenomena framed the Statue’s crown. These are complex interactions of light with small ice crystals suspended in the air. This rare atmospheric condition created an extraordinary scene: a perfect solar halo, accompanied by parhelia (so-called “false suns”), a parhelic arc and a superior tangent arc.” Thank you, Dario!
More halo photos from our friends
Everyone sees his or her own halo. That’s because – for every individual – a solar or lunar halo is made of light reflecting and refracting from different ice crystals in high, thin cirrus clouds. Image via Vincenzo Mirabella/ NASA. Used with permission.View at EarthSky Community Photos. | Amrinderjit Singh captured this photo from India on December 12, 2025, and wrote: “At 2200 meters high in the mountains, the sky offered its beauty by displaying a halo around the sun and I was right there to capture this beautiful landscape.” Thank you, Amrinderjit!View at EarthSky Community Photos. | Teresa Raines captured this image from Arizona on January 4, 2026, and wrote: “Lunar halo, with Orion in the bottom right corner, Jupiter next to moon peeking through top palm tree frond.” Thank you, Teresa!Eliot Herman wrote on May 5, 2018: “This shows the change that occurred over 7 minutes as a lunar halo emerged. It then persisted for about 40 minutes and disappeared with increasing clouds. Although it appears the halo is forming from an odd shape, what is actually illuminated is the edge of the clouds just before the halo formed as the clouds drifted in front of the moon. But it does have a nice illusion of an odd-shaped halo then becoming round.” Used with permission.
Bottom line: High, thin cirrus clouds drifting high above your head create the halos you see around the sun or moon. The halos are from tiny ice crystals in Earth’s atmosphere. They do it by refracting and reflecting the light. Lunar halos are signs that storms are nearby.
We tell you all you need to know about halos in our YouTube video here. Don’t forget to subscribe!
What causes halos?
Have you ever looked up and spotted a large ring of light around the sun or moon? Scientists refer to these as 22-degree halos. They got that name because the radius of the circle is always approximately 22 degrees.
There’s an old weather saying: ring around the moon means rain soon. There’s truth to this saying, because high cirrus clouds often come before a storm. Notice in these photos that the sky looks fairly clear. After all, you can see the sun or moon. And yet halos are a sign of high, thin cirrus clouds drifting 20,000 feet (6 km) or more above our heads.
These clouds contain millions of tiny ice crystals. The halos you see are caused by both refraction, or splitting of light, and also by reflection, or glints of light from these ice crystals. The crystals must be oriented and positioned just so with respect to your eye, for the halo to appear.
That’s why, like rainbows, halos around the sun – or moon – are personal. Everyone sees their own unique halo, made by the ice crystals from their point of view. So they are different from the ice crystals making the halo of a person standing next to you.
View at EarthSky Community Photos. | Roberto Ortu captured this moon halo on February 2, 2026, in Italy and wrote: “A moon halo has an apparent radius of 22 degrees and forms around the moon due to refraction by hexagonal-shaped ice crystals that are present in Earth’s atmosphere.” Thank you, Roberto! Notice that – unlike solar halos, which can be colorful – lunar halos are mostly colorless.
A word of caution for photographers
Take care when photographing solar halos. Pointing a camera directly at the unobscured sun can damage it. Never look directly at the sun, even when it is less bright through clouds or fog.
Are halos more common at high latitudes?
We asked Les Cowley of the website Atmospheric Optics if halos around the sun and moon are more frequently seen at high latitudes and less commonly seen closer to the equator. He said:
That’s a good question that is not easy to answer accurately because no halo frequency statistics are collected except in one or two mid-latitude European countries.
We need to distinguish between (a) halos formed by low level diamond dust during very cold weather and (b) halos formed by ice crystals in high cirrus cloud.
Obviously (a) halos only occur in polar regions or countries with very cold winters (Canada for example is not high latitude).
(b) Halos can occur anywhere on the planet during winter or summer. Their frequency depends on the frequency of cirrus coverage and whether it has had a history such that it contains halo forming crystals. The latter is hard to predict. For example, there are major differences in halo frequencies and types of halos across even 200 miles [300 km] in the U.K.
Halos are made by both refraction and reflection ice crystals, such as these, in this photo by Walt Tate. Image via Walt Tate/ Atmospheric Optics. Used with permission.
If you see a halo, notice this!
Because moonlight isn’t very bright, lunar halos are mostly colorless. However, you might notice red on the inside and blue on the outside of the halo. These colors are more noticeable in halos around the sun. If you do see a halo around the moon or sun, notice that the inner edge is sharp, while the outer edge is more diffuse. Also, notice that the sky surrounding the halo is darker than the rest of the sky.
Halo photos from EarthSky’s Community
View at EarthSky Community Photos. | Samit Saha captured this image on January 30, 2026, and wrote: “A bright lunar halo surrounds the moon on a bone-chilling winter night in India. The circular ring formed as moonlight passed through countless hexagonal ice crystals suspended in high, thin cirrostratus clouds, creating the classic 22-degree halo. Snow-covered hills beneath the sky emphasize the clarity and depth of the winter atmosphere. The wide-field view reveals several familiar constellations – Orion, Taurus, Gemini, and the Pleiades – along with the bright planet Jupiter, all sharing the frame with the glowing halo. Such halos often signal approaching weather changes, yet for a brief moment, the sky offered a rare balance of atmospheric optics and celestial geometry, captured in a single exposure.” Thank you, Samit!View at EarthSky Community Photos. | Bonnie Swan captured this image in Wisconsin on January 21, 2026, and wrote: “While driving east early in the morning, the halo and sun dogs around the rising sun continued to be very bright, when I found a vantage point to get the whole image, I had to pull over to capture it!” Thank you, Bonnie!View at EarthSky Community Photos. | Dario Giannobile captured this in Manhattan on December 12, 2025, and wrote: “In a handheld shot of the Statue of Liberty taken from the ferry connecting Ellis Island to Manhattan, with seagulls crossing the sky, a series of rare optical phenomena framed the Statue’s crown. These are complex interactions of light with small ice crystals suspended in the air. This rare atmospheric condition created an extraordinary scene: a perfect solar halo, accompanied by parhelia (so-called “false suns”), a parhelic arc and a superior tangent arc.” Thank you, Dario!
More halo photos from our friends
Everyone sees his or her own halo. That’s because – for every individual – a solar or lunar halo is made of light reflecting and refracting from different ice crystals in high, thin cirrus clouds. Image via Vincenzo Mirabella/ NASA. Used with permission.View at EarthSky Community Photos. | Amrinderjit Singh captured this photo from India on December 12, 2025, and wrote: “At 2200 meters high in the mountains, the sky offered its beauty by displaying a halo around the sun and I was right there to capture this beautiful landscape.” Thank you, Amrinderjit!View at EarthSky Community Photos. | Teresa Raines captured this image from Arizona on January 4, 2026, and wrote: “Lunar halo, with Orion in the bottom right corner, Jupiter next to moon peeking through top palm tree frond.” Thank you, Teresa!Eliot Herman wrote on May 5, 2018: “This shows the change that occurred over 7 minutes as a lunar halo emerged. It then persisted for about 40 minutes and disappeared with increasing clouds. Although it appears the halo is forming from an odd shape, what is actually illuminated is the edge of the clouds just before the halo formed as the clouds drifted in front of the moon. But it does have a nice illusion of an odd-shaped halo then becoming round.” Used with permission.
Bottom line: High, thin cirrus clouds drifting high above your head create the halos you see around the sun or moon. The halos are from tiny ice crystals in Earth’s atmosphere. They do it by refracting and reflecting the light. Lunar halos are signs that storms are nearby.
The March equinox is coming up fast. It’ll come at 14:46 UTC (9:46 a.m. CDT) on March 20, 2026. And here’s a little-known equinox phenomenon: the sun sets faster around the time of an equinox. The fastest sunrises happen at or near the equinoxes, too. On the other hand, the slowest sunsets (and sunrises) happen around the solstices. It’s true whether you live in Earth’s Northern or Southern Hemisphere.
By the way, when we say sunset here, we’re talking about the actual number of minutes it takes for the body of the sun to sink below the western horizon.
So why does it happen? Why does the body of the sun fall below the horizon so quickly at equinox-time? It’s because, at every equinox, the sun rises due east and sets due west. That means – on the day of an equinox – the setting sun hits the horizon at its steepest possible angle.
The equinox is an event that takes place in Earth’s orbit around the sun. Image via National Weather Service/ weather.gov.
Year’s slowest sunsets and sunrises
Meanwhile, at a solstice, the sun is setting farthest north or farthest south of due west. And, the farther the sun sets from due west along the horizon, the shallower the angle of the setting sun. So that means a longer duration for sunset at the solstices.
Also, the sunset duration varies by latitude. Farther north or south on the Earth’s globe, the duration of sunset lasts longer. So, closer to the equator, the duration is shorter. But let’s just consider one latitude, 40 degrees north, the latitude of Denver or Philadelphia in the United States; parts of Spain; and Beijing, China.
At that latitude, on the day of equinox, the sun sets in about 2 3/4 minutes.
On the other hand, the solstice sun sets in roughly 3 1/4 minutes at 40 degrees latitude.
Sunset images from the EarthSky community
View at EarthSky Community Photos. | Teresa Molinaro captured this image on August 28, 2024, in Italy. Teresa wrote: “A very intense dawn occurred on the morning of late September; and in the seaside village everything was silent.” Thank you, Teresa!View at EarthSky Community Photos. | Peter Lowenstein captured these images and wrote: “Equinox sunsets before and after equinox sunrise on 23 September. The instant of the Southern Hemisphere spring equinox in 2023 was at 6.50 UTC on 23 September. This means it was possible to record two equinox sunsets one on the 22nd a few hours before and another a few hours after the equinox sunrise on the 23rd. These are shown in the accompanying composite of three 9 video frame montages.” Thank you, Peter!
Bottom line: The fastest sunsets and sunrises of the year are happening now, around the time of the September equinox.
The March equinox is coming up fast. It’ll come at 14:46 UTC (9:46 a.m. CDT) on March 20, 2026. And here’s a little-known equinox phenomenon: the sun sets faster around the time of an equinox. The fastest sunrises happen at or near the equinoxes, too. On the other hand, the slowest sunsets (and sunrises) happen around the solstices. It’s true whether you live in Earth’s Northern or Southern Hemisphere.
By the way, when we say sunset here, we’re talking about the actual number of minutes it takes for the body of the sun to sink below the western horizon.
So why does it happen? Why does the body of the sun fall below the horizon so quickly at equinox-time? It’s because, at every equinox, the sun rises due east and sets due west. That means – on the day of an equinox – the setting sun hits the horizon at its steepest possible angle.
The equinox is an event that takes place in Earth’s orbit around the sun. Image via National Weather Service/ weather.gov.
Year’s slowest sunsets and sunrises
Meanwhile, at a solstice, the sun is setting farthest north or farthest south of due west. And, the farther the sun sets from due west along the horizon, the shallower the angle of the setting sun. So that means a longer duration for sunset at the solstices.
Also, the sunset duration varies by latitude. Farther north or south on the Earth’s globe, the duration of sunset lasts longer. So, closer to the equator, the duration is shorter. But let’s just consider one latitude, 40 degrees north, the latitude of Denver or Philadelphia in the United States; parts of Spain; and Beijing, China.
At that latitude, on the day of equinox, the sun sets in about 2 3/4 minutes.
On the other hand, the solstice sun sets in roughly 3 1/4 minutes at 40 degrees latitude.
Sunset images from the EarthSky community
View at EarthSky Community Photos. | Teresa Molinaro captured this image on August 28, 2024, in Italy. Teresa wrote: “A very intense dawn occurred on the morning of late September; and in the seaside village everything was silent.” Thank you, Teresa!View at EarthSky Community Photos. | Peter Lowenstein captured these images and wrote: “Equinox sunsets before and after equinox sunrise on 23 September. The instant of the Southern Hemisphere spring equinox in 2023 was at 6.50 UTC on 23 September. This means it was possible to record two equinox sunsets one on the 22nd a few hours before and another a few hours after the equinox sunrise on the 23rd. These are shown in the accompanying composite of three 9 video frame montages.” Thank you, Peter!
Bottom line: The fastest sunsets and sunrises of the year are happening now, around the time of the September equinox.
