View at EarthSky Community Photos. | Karl Diefenderfer of Quakertown, Pennsylvania, wrote: “Vibrant winter’s solstice sunrise.” Thank you, Karl! By the way, the December solstice starts the year’s shortest season.
The year’s shortest season has begun
Did you know that Earth’s seasons are slightly different lengths? And by season, we mean the time between a solstice and an equinox. The season – between the December solstice and March equinox – is a touch shy of 89 days. So it’s Earth’s shortest season.
Here are the lengths of the astronomical seasons:
December solstice to March equinox: 88.99 days
March equinox to June solstice: 92.76 days
June solstice to September equinox: 93.65 days
September equinox to December solstice: 89.84 days
The December solstice occurs when the sun reaches its southernmost point in our sky for this year. That is what’s happening this week, at 9:21 UTC on December 21, 2024 (3:21 a.m. CST). This solstice marks an unofficial beginning of the winter season in the Northern Hemisphere, and the start of the summer season in the Southern Hemisphere. Unofficial? What? That’s correct. While no government body has decreed it shall be so, we all generally agree that the solstices and equinoxes are hallmarks of seasonal change.
So no matter where you are on Earth, the season – between the December solstice and March equinox – marks the beginning of your shortest season.
Contrast the number of days in the present season with that of Earth’s longest season – the time between the June solstice and September equinox – in other words, a Northern Hemisphere summer or Southern Hemisphere winter. Because that is Earth’s longest season and lasts 93.65 days.
But the current season is nearly five days shorter. Why?
The reason for the shortest season
As a matter of fact, every year in early January, the Earth swings closest to the sun for the year. And this nearest point is called Earth’s perihelion. Because Earth reaches perihelion in early January, our planet moves most swiftly in its orbit around now. That is just physics: Planets move faster when they are closer to the sun than when they are farther from the sun. And it’s why a Northern Hemisphere winter, or Southern Hemisphere summer, is the shortest of the four seasons. It simply takes us fewer days at this time of year to move between a solstice and an equinox.
On the other hand, in early July, Earth is at aphelion – or farthest from the sun – and moving most slowly in its orbit. So that’s why the longest season occurs at that time.
But of course, seasons change
According to the computational wizard Jean Meeus, a Northern Hemisphere winter or Southern Hemisphere summer became the shortest season after the year 1246. The astronomical season between the December solstice and the March equinox will reach a minimum value of 88.71 days around the year 3500, and will continue to reign as the shortest season until about the year 6430.
The lights of cities from the nightside of Earth. This composite image of Asia and Australia at night used data from the Suomi NPP satellite. Image via NASA.
Bottom line: Earth’s shortest season begins at the solstice on December 21, 2024. The coming season – Northern Hemisphere winter or Southern Hemisphere summer – is a touch shy of 89 days in length.
View at EarthSky Community Photos. | Karl Diefenderfer of Quakertown, Pennsylvania, wrote: “Vibrant winter’s solstice sunrise.” Thank you, Karl! By the way, the December solstice starts the year’s shortest season.
The year’s shortest season has begun
Did you know that Earth’s seasons are slightly different lengths? And by season, we mean the time between a solstice and an equinox. The season – between the December solstice and March equinox – is a touch shy of 89 days. So it’s Earth’s shortest season.
Here are the lengths of the astronomical seasons:
December solstice to March equinox: 88.99 days
March equinox to June solstice: 92.76 days
June solstice to September equinox: 93.65 days
September equinox to December solstice: 89.84 days
The December solstice occurs when the sun reaches its southernmost point in our sky for this year. That is what’s happening this week, at 9:21 UTC on December 21, 2024 (3:21 a.m. CST). This solstice marks an unofficial beginning of the winter season in the Northern Hemisphere, and the start of the summer season in the Southern Hemisphere. Unofficial? What? That’s correct. While no government body has decreed it shall be so, we all generally agree that the solstices and equinoxes are hallmarks of seasonal change.
So no matter where you are on Earth, the season – between the December solstice and March equinox – marks the beginning of your shortest season.
Contrast the number of days in the present season with that of Earth’s longest season – the time between the June solstice and September equinox – in other words, a Northern Hemisphere summer or Southern Hemisphere winter. Because that is Earth’s longest season and lasts 93.65 days.
But the current season is nearly five days shorter. Why?
The reason for the shortest season
As a matter of fact, every year in early January, the Earth swings closest to the sun for the year. And this nearest point is called Earth’s perihelion. Because Earth reaches perihelion in early January, our planet moves most swiftly in its orbit around now. That is just physics: Planets move faster when they are closer to the sun than when they are farther from the sun. And it’s why a Northern Hemisphere winter, or Southern Hemisphere summer, is the shortest of the four seasons. It simply takes us fewer days at this time of year to move between a solstice and an equinox.
On the other hand, in early July, Earth is at aphelion – or farthest from the sun – and moving most slowly in its orbit. So that’s why the longest season occurs at that time.
But of course, seasons change
According to the computational wizard Jean Meeus, a Northern Hemisphere winter or Southern Hemisphere summer became the shortest season after the year 1246. The astronomical season between the December solstice and the March equinox will reach a minimum value of 88.71 days around the year 3500, and will continue to reign as the shortest season until about the year 6430.
The lights of cities from the nightside of Earth. This composite image of Asia and Australia at night used data from the Suomi NPP satellite. Image via NASA.
Bottom line: Earth’s shortest season begins at the solstice on December 21, 2024. The coming season – Northern Hemisphere winter or Southern Hemisphere summer – is a touch shy of 89 days in length.
For the latest on Parker Solar Probe, watch the livestream above at 12:15 CST (18:15 UTC) on Friday, December 20, 2024, with EarthSky founder Deborah Byrd and heliophysicist C. Alex Young of NASA Goddard Spaceflight Center, co-author of EarthSky’s daily sun news update. Join us in marveling at a spacecraft that can touch the sun!
Parker Solar Probe’s closest sun flyby on December 24
On November 6, 2024, the Parker Solar Probe completed its 7th and final gravity assist with Venus, in preparation for the world’s closest encounter of a spacecraft with our sun. And that’s saying something. Already, in 2021, Parker Solar Probe became the first spacecraft ever to touch the sun, that is to fly within the sun’s corona or outer atmosphere. But it’s due to come closer still. On December 24, 2024, Parker will break its own record when it comes within 3.86 million miles (6.2 million km) of the sun’s surface.
As the spacecraft once again becomes the closest humanmade object to the sun, it will be out of contact with mission control. In fact, we won’t hear how Parker’s trip was until three days later (!), on December 27, 2024. That’s when the probe will send a beacon back to Earth. But, even then, Parker Solar Probe’s mission won’t be over. It’ll complete two more close encounters with the sun at the same distance as the December 24 event. The seven-year mission should conclude sometime in 2025.
Needless to say, the results from Parker Solar Probe’s mission will be unprecedented. And sun scientists are excited about this spacecraft’s data-gathering ability so close to our local star. At this month’s American Geophysical Union meeting in Washington, D.C., sun scientists were particularly focused on space weather. That is, they were excited about increasing their understanding of how flares on the sun can lead to conditions in near-Earth space that affect our world’s magnetic field. The effects can include beautiful auroral displays. And they can include fried satellite and power grid components. These scientists believe the results from Parker Solar Probe will help keep our human society safer from the effects of solar flares. NASA said in a statement:
The primary goals are to examine the acceleration of solar wind through the movement of heat and energy in the sun’s corona in addition to study solar energetic particles.
Dr. C. Alex Young, co-author of EarthSky’s daily sun news update, talked about Parker Solar Probe and about what scientists were buzzing about at the AGU meeting, in this EarthSky livestream:
Hear EarthSky founder Deborah Byrd – and Dr. C. Alex Young of NASA Goddard Space Flight Center, co-author of EarthSky’s daily sun news update – discuss what scientists were saying at this year’s AGU meeting, in the video above.
When Parker Solar Probe 1st touched the sun in 2021
Parker Solar Probe became the first spacecraft to literally touch the sun on April 28, 2021. Scientists made the announcement on December 14, 2021, at the American Geophysical Union meeting in New Orleans. They said the Parker Solar Probe flew through the sun’s upper atmosphere, its wispy corona. The corona is that fiery-looking outer layer of the sun that appears around the moon’s silhouette during total solar eclipses.
Parker Solar Probe has been sampling the corona’s particles and magnetic fields. It’s been making discoveries more distant spacecraft can’t make. For example, the solar wind is a stream of charged particles released from the sun’s corona. Parker Solar Probe found zigzag structures in the solar wind that scientists are calling switchbacks.
Also on December 14, 2021, the peer-reviewedPhysical Review Letterspublished the results of Parker Solar Probe’s first venture into the sun’s upper atmosphere.
Thomas Zurbuchen, the associate administrator for the Science Mission Directorate at NASA Headquarters in Washington, said:
Touching the sun is a monumental moment for solar science and a truly remarkable feat. Not only does this milestone provide us with deeper insights into our sun’s evolution and its impacts on our solar system, but everything we learn about our own star also teaches us more about stars in the rest of the universe.
In addition, Nour Raouafi of Johns Hopkins Applied Physics Laboratory said:
Flying so close to the sun, Parker Solar Probe now senses conditions in the magnetically dominated layer of the solar atmosphere – the corona – that we never could before. We see evidence of being in the corona in magnetic field data, solar wind data, and visually in images. We can actually see the spacecraft flying through coronal structures that can be observed during a total solar eclipse.
What does touching the sun look like? For one thing, as Parker Solar Probe passed through our sun’s corona, or wispy outer atmosphere, it flew by structures called coronal streamers. These structures are the bright features moving upward in the upper images above, and angled downward in the lower row. They are the streamers visible around the dark moon silhouette during total solar eclipses. And Parker Solar Probe touched and measured these streamers for the first time. Image via NASA/ Johns Hopkins APL/ Naval Research Laboratory.
Watch a video about when Parker Solar Probe touched the sun
Reaching the Alfvén critical surface
NASA launched Parker toward the sun in 2018. As Parker circled closer and closer during several flybys, scientists looked for indications that it had reached the Alfvén critical surface. The Alfvén critical surface is the point that marks the end of the solar atmosphere and the beginning of the solar wind. While the sun doesn’t have a solid surface, it does have a boundary. The boundary is the point at which solar material bound to the sun by gravity and magnetic forces ends.
Solar material energetic enough to cross the Alfvén critical surface becomes the solar wind, dragging magnetic field lines with it. Once the material crosses this boundary, the wind is moving too fast to ever travel back to the sun, severing the connection.
Scientists estimated the Alfvén critical surface was somewhere between 10 to 20 solar radii from the surface of the sun. This is equal to 4.3 to 8.6 million miles (7 to 13.8 million km) from the sun. When Parker finally spiraled close enough to the sun to detect that it had crossed the Alfvén critical surface, it was 18.8 solar radii (around 8 million miles or 13 million km) above the solar surface. For the first time, on April 28, 2021, Parker entered the solar atmosphere.
Justin Kasper of BWX Technologies Inc. and the University of Michigan, said:
We were fully expecting that, sooner or later, we would encounter the corona for at least a short duration of time. But it is very exciting that we’ve already reached it.
Artist’s concept shows NASA’s Parker Solar Probe. It is the 1st spacecraft to touch the sun. Image via NASA.
The peculiarities of the sun’s border
Parker Solar Probe discovered that this boundary – the Alfvén critical surface – isn’t smooth and round. The edge has wrinkles. The spacecraft passed through spikes and valleys as it dove in and out of the boundary. Parker got as close as just under 15 solar radii (around 7 million miles or 11 million km) from the sun’s surface. In this region it passed through a pseudostreamer, a feature in the corona. Pseudostreamers are towering structures that rise above the sun’s surface that we can see during solar eclipses.
Being inside the pseudostreamer was like being inside the eye of a hurricane. The conditions were quieter and slower, easing the barrage of particles on the spacecraft. In this region, magnetic fields were the dominate force over particles, providing proof that Parker was inside the Alfvén critical surface.
Parker only spent a few hours in the sun’s corona. But the spacecraft will continue to spiral closer, aiming for a distance of 8.86 solar radii (3.83 million miles or 6.1 million km) from the surface. Its next flyby, in January 2022, should dip Parker into the corona again. Nicola Fox of NASA said:
I’m excited to see what Parker finds as it repeatedly passes through the corona in the years to come. The opportunity for new discoveries is boundless.
View larger. | This graphic represents Parker Solar Probe’s distances from the sun during its milestones and discoveries. Image via NASA/ Mary P. Hrybyk-Keith.
Solar maximum and switchbacks
The sun’s corona expands in size during periods of higher solar activity. The sun is currently in solar cycle 25, which should reach a peak in activity (solar maximum) around 2025. This expansion will allow Parker to spend more time inside the corona. Kasper said:
It is a really important region to get into because we think all sorts of physics potentially turn on. And now we’re getting into that region and hopefully going to start seeing some of these physics and behaviors.
One behavior of the sun that Parker is already investigating is that of strange kinks in the solar wind’s magnetic field lines. Scientists first spotted these switchbacks in the mid-1990s and thought they were limited to the sun’s polar regions. Parker encountered the zigzags in the solar wind in 2019, finding that they are common, not rare. And now that Parker is twice as close to the sun as it was in 2019, it can see where these kinky structures originate: the solar surface. Its findings confirm that the switchbacks come from the photosphere, or the visible surface of the sun.
Parker discovered that the switchbacks occur in patches and have a higher percentage of helium – a sign that they came from the photosphere – than other elements. Parker also found that the patches of switchbacks aligned with magnetic funnels that emerge from the photosphere between convection cell structures called supergranules.
Now, scientists think these magnetic funnels may also be the source of the fast solar wind. Stuart Bale of the University of California, Berkeley, said:
The structure of the regions with switchbacks matches up with a small magnetic funnel structure at the base of the corona. This is what we expect from some theories, and this pinpoints a source for the solar wind itself.
Parker Solar Probe: More mysteries
As astronomers learn more about the solar wind and switchbacks, they hope it will help them unlock a long-standing mystery in astronomy: why the corona is so much hotter than the surface of the sun. Bale said:
My instinct is, as we go deeper into the mission and lower and closer to the sun, we’re going to learn more about how magnetic funnels are connected to the switchbacks and hopefully resolve the question of what process makes them.
Scientists hope to learn more about the superheated corona and what pushes the solar wind to supersonic speeds. This will also help them understand and forecast space weather events that impact Earth’s environment and sometimes human technology.
Joseph Smith, Parker program executive at NASA Headquarters, said:
It’s really exciting to see our advanced technologies succeed in taking Parker Solar Probe closer to the sun than we’ve ever been, and to be able to return such amazing science. We look forward to seeing what else the mission discovers as it ventures even closer in the coming years.
Bottom line: The Parker Solar Probe will make its closest pass by the sun on December 24, 2024. It will be even closer than when it 1st “touched the sun” in 2021.
For the latest on Parker Solar Probe, watch the livestream above at 12:15 CST (18:15 UTC) on Friday, December 20, 2024, with EarthSky founder Deborah Byrd and heliophysicist C. Alex Young of NASA Goddard Spaceflight Center, co-author of EarthSky’s daily sun news update. Join us in marveling at a spacecraft that can touch the sun!
Parker Solar Probe’s closest sun flyby on December 24
On November 6, 2024, the Parker Solar Probe completed its 7th and final gravity assist with Venus, in preparation for the world’s closest encounter of a spacecraft with our sun. And that’s saying something. Already, in 2021, Parker Solar Probe became the first spacecraft ever to touch the sun, that is to fly within the sun’s corona or outer atmosphere. But it’s due to come closer still. On December 24, 2024, Parker will break its own record when it comes within 3.86 million miles (6.2 million km) of the sun’s surface.
As the spacecraft once again becomes the closest humanmade object to the sun, it will be out of contact with mission control. In fact, we won’t hear how Parker’s trip was until three days later (!), on December 27, 2024. That’s when the probe will send a beacon back to Earth. But, even then, Parker Solar Probe’s mission won’t be over. It’ll complete two more close encounters with the sun at the same distance as the December 24 event. The seven-year mission should conclude sometime in 2025.
Needless to say, the results from Parker Solar Probe’s mission will be unprecedented. And sun scientists are excited about this spacecraft’s data-gathering ability so close to our local star. At this month’s American Geophysical Union meeting in Washington, D.C., sun scientists were particularly focused on space weather. That is, they were excited about increasing their understanding of how flares on the sun can lead to conditions in near-Earth space that affect our world’s magnetic field. The effects can include beautiful auroral displays. And they can include fried satellite and power grid components. These scientists believe the results from Parker Solar Probe will help keep our human society safer from the effects of solar flares. NASA said in a statement:
The primary goals are to examine the acceleration of solar wind through the movement of heat and energy in the sun’s corona in addition to study solar energetic particles.
Dr. C. Alex Young, co-author of EarthSky’s daily sun news update, talked about Parker Solar Probe and about what scientists were buzzing about at the AGU meeting, in this EarthSky livestream:
Hear EarthSky founder Deborah Byrd – and Dr. C. Alex Young of NASA Goddard Space Flight Center, co-author of EarthSky’s daily sun news update – discuss what scientists were saying at this year’s AGU meeting, in the video above.
When Parker Solar Probe 1st touched the sun in 2021
Parker Solar Probe became the first spacecraft to literally touch the sun on April 28, 2021. Scientists made the announcement on December 14, 2021, at the American Geophysical Union meeting in New Orleans. They said the Parker Solar Probe flew through the sun’s upper atmosphere, its wispy corona. The corona is that fiery-looking outer layer of the sun that appears around the moon’s silhouette during total solar eclipses.
Parker Solar Probe has been sampling the corona’s particles and magnetic fields. It’s been making discoveries more distant spacecraft can’t make. For example, the solar wind is a stream of charged particles released from the sun’s corona. Parker Solar Probe found zigzag structures in the solar wind that scientists are calling switchbacks.
Also on December 14, 2021, the peer-reviewedPhysical Review Letterspublished the results of Parker Solar Probe’s first venture into the sun’s upper atmosphere.
Thomas Zurbuchen, the associate administrator for the Science Mission Directorate at NASA Headquarters in Washington, said:
Touching the sun is a monumental moment for solar science and a truly remarkable feat. Not only does this milestone provide us with deeper insights into our sun’s evolution and its impacts on our solar system, but everything we learn about our own star also teaches us more about stars in the rest of the universe.
In addition, Nour Raouafi of Johns Hopkins Applied Physics Laboratory said:
Flying so close to the sun, Parker Solar Probe now senses conditions in the magnetically dominated layer of the solar atmosphere – the corona – that we never could before. We see evidence of being in the corona in magnetic field data, solar wind data, and visually in images. We can actually see the spacecraft flying through coronal structures that can be observed during a total solar eclipse.
What does touching the sun look like? For one thing, as Parker Solar Probe passed through our sun’s corona, or wispy outer atmosphere, it flew by structures called coronal streamers. These structures are the bright features moving upward in the upper images above, and angled downward in the lower row. They are the streamers visible around the dark moon silhouette during total solar eclipses. And Parker Solar Probe touched and measured these streamers for the first time. Image via NASA/ Johns Hopkins APL/ Naval Research Laboratory.
Watch a video about when Parker Solar Probe touched the sun
Reaching the Alfvén critical surface
NASA launched Parker toward the sun in 2018. As Parker circled closer and closer during several flybys, scientists looked for indications that it had reached the Alfvén critical surface. The Alfvén critical surface is the point that marks the end of the solar atmosphere and the beginning of the solar wind. While the sun doesn’t have a solid surface, it does have a boundary. The boundary is the point at which solar material bound to the sun by gravity and magnetic forces ends.
Solar material energetic enough to cross the Alfvén critical surface becomes the solar wind, dragging magnetic field lines with it. Once the material crosses this boundary, the wind is moving too fast to ever travel back to the sun, severing the connection.
Scientists estimated the Alfvén critical surface was somewhere between 10 to 20 solar radii from the surface of the sun. This is equal to 4.3 to 8.6 million miles (7 to 13.8 million km) from the sun. When Parker finally spiraled close enough to the sun to detect that it had crossed the Alfvén critical surface, it was 18.8 solar radii (around 8 million miles or 13 million km) above the solar surface. For the first time, on April 28, 2021, Parker entered the solar atmosphere.
Justin Kasper of BWX Technologies Inc. and the University of Michigan, said:
We were fully expecting that, sooner or later, we would encounter the corona for at least a short duration of time. But it is very exciting that we’ve already reached it.
Artist’s concept shows NASA’s Parker Solar Probe. It is the 1st spacecraft to touch the sun. Image via NASA.
The peculiarities of the sun’s border
Parker Solar Probe discovered that this boundary – the Alfvén critical surface – isn’t smooth and round. The edge has wrinkles. The spacecraft passed through spikes and valleys as it dove in and out of the boundary. Parker got as close as just under 15 solar radii (around 7 million miles or 11 million km) from the sun’s surface. In this region it passed through a pseudostreamer, a feature in the corona. Pseudostreamers are towering structures that rise above the sun’s surface that we can see during solar eclipses.
Being inside the pseudostreamer was like being inside the eye of a hurricane. The conditions were quieter and slower, easing the barrage of particles on the spacecraft. In this region, magnetic fields were the dominate force over particles, providing proof that Parker was inside the Alfvén critical surface.
Parker only spent a few hours in the sun’s corona. But the spacecraft will continue to spiral closer, aiming for a distance of 8.86 solar radii (3.83 million miles or 6.1 million km) from the surface. Its next flyby, in January 2022, should dip Parker into the corona again. Nicola Fox of NASA said:
I’m excited to see what Parker finds as it repeatedly passes through the corona in the years to come. The opportunity for new discoveries is boundless.
View larger. | This graphic represents Parker Solar Probe’s distances from the sun during its milestones and discoveries. Image via NASA/ Mary P. Hrybyk-Keith.
Solar maximum and switchbacks
The sun’s corona expands in size during periods of higher solar activity. The sun is currently in solar cycle 25, which should reach a peak in activity (solar maximum) around 2025. This expansion will allow Parker to spend more time inside the corona. Kasper said:
It is a really important region to get into because we think all sorts of physics potentially turn on. And now we’re getting into that region and hopefully going to start seeing some of these physics and behaviors.
One behavior of the sun that Parker is already investigating is that of strange kinks in the solar wind’s magnetic field lines. Scientists first spotted these switchbacks in the mid-1990s and thought they were limited to the sun’s polar regions. Parker encountered the zigzags in the solar wind in 2019, finding that they are common, not rare. And now that Parker is twice as close to the sun as it was in 2019, it can see where these kinky structures originate: the solar surface. Its findings confirm that the switchbacks come from the photosphere, or the visible surface of the sun.
Parker discovered that the switchbacks occur in patches and have a higher percentage of helium – a sign that they came from the photosphere – than other elements. Parker also found that the patches of switchbacks aligned with magnetic funnels that emerge from the photosphere between convection cell structures called supergranules.
Now, scientists think these magnetic funnels may also be the source of the fast solar wind. Stuart Bale of the University of California, Berkeley, said:
The structure of the regions with switchbacks matches up with a small magnetic funnel structure at the base of the corona. This is what we expect from some theories, and this pinpoints a source for the solar wind itself.
Parker Solar Probe: More mysteries
As astronomers learn more about the solar wind and switchbacks, they hope it will help them unlock a long-standing mystery in astronomy: why the corona is so much hotter than the surface of the sun. Bale said:
My instinct is, as we go deeper into the mission and lower and closer to the sun, we’re going to learn more about how magnetic funnels are connected to the switchbacks and hopefully resolve the question of what process makes them.
Scientists hope to learn more about the superheated corona and what pushes the solar wind to supersonic speeds. This will also help them understand and forecast space weather events that impact Earth’s environment and sometimes human technology.
Joseph Smith, Parker program executive at NASA Headquarters, said:
It’s really exciting to see our advanced technologies succeed in taking Parker Solar Probe closer to the sun than we’ve ever been, and to be able to return such amazing science. We look forward to seeing what else the mission discovers as it ventures even closer in the coming years.
Bottom line: The Parker Solar Probe will make its closest pass by the sun on December 24, 2024. It will be even closer than when it 1st “touched the sun” in 2021.
We have our best views of Mars only once every 2 years. And that time is fast approaching! Watch a replay of our livestream for more information about Mars.
Mars can appear bright or faint in our sky. 2024 has been mostly a faint year, but Mars has been steadily brightening, and it’s very noticeable now, nearly as bright as the sky’s brightest star. The time to start observing Mars for this two-year period is here.
Mars is growing brighter as Earth catches up with Mars, in our smaller, faster orbit around the sun. The coming opposition of Mars – when Earth will pass between it and the sun, bringing Mars closest and brightest – will take place on January 15-16, 2025.
Start watching for Mars now. It’s up in the east by late evening, following blazing Jupiter across the sky.
Opposition for Mars last fell on December 7-8, 2022. That’s when our planet Earth last flew between Mars and the sun. Mars will reach opposition again at 3 UTC on January 16, 2025. Throughout November 2024, Mars has been growing brighter. It’s now easy to spot late at night through dawn. How to see Mars in the sky: Mars is now nearly as bright as Sirius, the sky’s brightest star. It was near the moon on December 17, 2024. Mars, Jupiter and Sirius will appear as “New Year’s stars” on December 31. Note: Mars reaches opposition about every 26 months, or about every two Earth years. It’s now racing toward its January 15-16, 2025, opposition. Wait. That’s not quite right. It’s Earth that’s racing up behind Mars, in our smaller, faster orbit around the sun.
Mars in December 2024
View at EarthSky Community Photos. | Richard Swieca at Hillsboro Beach, Florida, caught Mars and the waning moon rising over the Atlantic Ocean on the evening of December 17, 2024. Watch for Mars! It’s bright, soon to be at its brightest. Thank you, Richard! By the way, following to this view caught by Richard, the moon will occult or pass in front of Mars as seen from parts of Canada, Greenland, eastern Russia and Alaska and other locations.In December 2024, Mars lies in front of the constellation of Cancer the Crab and not far from the twin stars of Gemini: Castor and Pollux. It’s rising in mid-evening, not far behind blazing Jupiter, and is obvious in the sky before dawn. Mars will be as bright as Sirius, the sky’s brightest star, by the end of December. It will be at its closest to Earth in mid-January 2025. Chart via EarthSky.
Sometimes, Mars is faint
Mars last reached opposition on December 8, 2022. It remained bright through early 2023, then started to rapidly fade through the end of the year. Mars reached superior conjunction – when it passed behind the sun as viewed from Earth – on November 18, 2023. It began 2024 as a faint object, far across the solar system from us. But now Mars is getting bright again.
The geometry of Mars’ orbit is such that it spends much longer periods of time at large distances from the Earth than it does close to us, which provides added incentive to observe it in the weeks around opposition. When it passes opposition, every 2 years, Mars appears large and bright for only a few weeks. Here’s a comparison of the apparent size of Mars when seen at its closest opposition, around its opposition in 2025, and at its farthest opposition. Also shown is how Mars appears when it’s most distant from the Earth at solar conjunction. Image via Dominic Ford/ In-The-Sky.org. Used with permission.
Sometimes, Mars is bright
Mars’ dramatic swings in brightness (and its red color) are why the early stargazers named Mars for their god of war.
Sometimes the war god rests. And sometimes he grows fierce! These changes are part of the reason Mars is so fascinating to watch in the night sky.
When Mars passes opposition, every 2 years, it appears large and bright for only a few weeks. The panel above shows the change in Mars’ apparent size from November 20, 2024, to March 12, 2025. Mars will appear 14.6 arcseconds wide on January 15, 2025. Image via Dominic Ford/ In-The-Sky.org. Used with permission.As Mars races towards its next opposition in January 2025, it’ll grow in apparent size and increase in brightness. Chart via Guy Ottewell’s 2024 Astronomical Calendar. Used with permission.
To understand why Mars varies so much in brightness in Earth’s sky, first realize that it isn’t a very big world. It’s only 4,219 miles (6,790 km) in diameter, making it only slightly more than half Earth’s size (7,922 miles or 12,750 km in diameter).
On the other hand, consider Mars in contrast to Jupiter, the biggest planet in our solar system. Jupiter is 86,881 miles (140,000 km) in diameter. As an illustration, more than 20 planets the size of Mars could be lined up side by side in front of Jupiter. Basically, Jupiter always looks bright, because it’s so big.
Not so for little Mars, however. Rather, its extremes in brightness have to do with its nearness (or lack of nearness) to Earth.
Mars isn’t very big, so its brightness – when it is bright – isn’t due to its bigness, as is true of Jupiter. Mars’ brightness, or lack of brightness, is all about how close we are to the red planet. It’s all about where Earth and Mars are, relative to each other, in their respective orbits around the sun. Image via NASA.
Future Martian oppositions
As mentioned above, the next opposition of Mars – when will appear at its brightest in Earth’s sky for that two-year period – will be January 2025. Check out the chart at C. Seligman’s Mars oppositions page that lists all oppositions of Mars from 1995 to 2037.
There’s a 15-year cycle of Mars, whereby the red planet is brighter and fainter at opposition. In July 2018, we were at the peak of the 2-year cycle – and the peak of the 15-year cycle – and Mars was very, very bright! In 2020, we were also at the peak of the 2-year cycle; however, Earth and Mars were farther apart at Mars’ opposition than they were in 2018. Still, 2020’s opposition of Mars was excellent. And, in December 2022, Mars had a good opposition but appeared smaller and dimmer than in 2020, since we were farther away from it. And the January 2025 opposition will find Mars smaller and dimmer than Mars was in 2022. Diagram by Roy L. Bishop. Copyright Royal Astronomical Society of Canada. Used with permission. Visit the RASC eStore to purchase the Observer’s Handbook, a necessary tool for all skywatchers.
EarthSky Community Photos
View at EarthSky Community Photos. | Paolo Bardelli of Italy made this composite image and said: “On January 16, 2025, Mars will be in opposition, the previous one occurred on December 8, 2022, when it became the brightest object in the night sky. During these periods, tracing the apparent motion of the red planet from evening to evening is very interesting, as a real ‘noose’ is created, with a double reversal of its movement. This put ancient sky observers in crisis at the time when the geocentric theory was dominant. Putting things in their place, it turned out to be a simple perspective effect, due to the mutual motion of Earth and Mars. This image is the sum of a sequence taken every useful evening, clouds permitting, from August 12, 2022, to March 22, 2023. The background is the sum of 22 shots of the area of the sky where Mars was located, the rich star field of the constellation del Toro (Taurus). By coincidence, in February 2023 the path of comet C/2022 E3 (ZTF) crossed the noose.” Thank you, Paolo!View at EarthSky Community Photos. | Miguel Ventura in Fafe, Portugal, captured this image on August 28, 2022, and wrote: “Every now and then and in addition to its natural beauty, the night sky and the whims of the universe offer us moments like this. With some planning and luck in the mix (truce from the clouds) I was able to photograph this magnificent alignment. We can see the Pleiades and the constellation of Taurus with the planet Mars between these 2 … below near the horizon the imposing constellation of Orion appears, announcing the autumn sky.” Thank you, Miguel!
Seeing red
Mars appears as a reddish light in the sky and, therefore, is often called the red planet. Other obvious red dots in the sky are reddish-orange Aldebaran and the famous red supergiant Betelgeuse. So, it is fun to contrast Mars’ color and intensity of red with that of Aldebaran or Betelgeuse.
And then there is red Antares. Antares is Greek for rival of Ares (Ares being the Greek name for Mars). Antares is sometimes said to be the anti-Mars due to its competing red color. For a few months every couple of years Mars is much brighter than Antares. Also, every couple of years Mars passes near Antares, as if taunting the star. Mars moves rapidly through the heavens and Antares is fixed to the starry firmament.
What makes them red?
Surface temperature is what determines the colors of the stars. The hottest stars are blue and the coolest stars are red. In fact, from hottest to coolest, the colors of stars range from blue, white, yellow, orange and red. And while the colors of stars might be hard to detect, some stars – like Aldebaran, Antares and Betelgeuse – are noticeably colorful.
On the other hand, Mars appears red for a different reason. It’s red because of iron oxide in the dust that covers this desert world. Iron oxide gives rust and blood its red color. Rovers on Mars sampled the Martian dust and determined it contains three colors: reds, browns and oranges. So those three colors are what you may see when you gaze upon Mars.
Do you see red when you look at Mars, Aldebaran, Antares and Betelgeuse? Are they the same color? Do you see any other colors of stars?
Bottom line: Mars was the bright red “star” near last night’s moon. Earth is racing up behind Mars in orbit now, about to catch up with it, bringing Mars to opposition in January 2025.
We have our best views of Mars only once every 2 years. And that time is fast approaching! Watch a replay of our livestream for more information about Mars.
Mars can appear bright or faint in our sky. 2024 has been mostly a faint year, but Mars has been steadily brightening, and it’s very noticeable now, nearly as bright as the sky’s brightest star. The time to start observing Mars for this two-year period is here.
Mars is growing brighter as Earth catches up with Mars, in our smaller, faster orbit around the sun. The coming opposition of Mars – when Earth will pass between it and the sun, bringing Mars closest and brightest – will take place on January 15-16, 2025.
Start watching for Mars now. It’s up in the east by late evening, following blazing Jupiter across the sky.
Opposition for Mars last fell on December 7-8, 2022. That’s when our planet Earth last flew between Mars and the sun. Mars will reach opposition again at 3 UTC on January 16, 2025. Throughout November 2024, Mars has been growing brighter. It’s now easy to spot late at night through dawn. How to see Mars in the sky: Mars is now nearly as bright as Sirius, the sky’s brightest star. It was near the moon on December 17, 2024. Mars, Jupiter and Sirius will appear as “New Year’s stars” on December 31. Note: Mars reaches opposition about every 26 months, or about every two Earth years. It’s now racing toward its January 15-16, 2025, opposition. Wait. That’s not quite right. It’s Earth that’s racing up behind Mars, in our smaller, faster orbit around the sun.
Mars in December 2024
View at EarthSky Community Photos. | Richard Swieca at Hillsboro Beach, Florida, caught Mars and the waning moon rising over the Atlantic Ocean on the evening of December 17, 2024. Watch for Mars! It’s bright, soon to be at its brightest. Thank you, Richard! By the way, following to this view caught by Richard, the moon will occult or pass in front of Mars as seen from parts of Canada, Greenland, eastern Russia and Alaska and other locations.In December 2024, Mars lies in front of the constellation of Cancer the Crab and not far from the twin stars of Gemini: Castor and Pollux. It’s rising in mid-evening, not far behind blazing Jupiter, and is obvious in the sky before dawn. Mars will be as bright as Sirius, the sky’s brightest star, by the end of December. It will be at its closest to Earth in mid-January 2025. Chart via EarthSky.
Sometimes, Mars is faint
Mars last reached opposition on December 8, 2022. It remained bright through early 2023, then started to rapidly fade through the end of the year. Mars reached superior conjunction – when it passed behind the sun as viewed from Earth – on November 18, 2023. It began 2024 as a faint object, far across the solar system from us. But now Mars is getting bright again.
The geometry of Mars’ orbit is such that it spends much longer periods of time at large distances from the Earth than it does close to us, which provides added incentive to observe it in the weeks around opposition. When it passes opposition, every 2 years, Mars appears large and bright for only a few weeks. Here’s a comparison of the apparent size of Mars when seen at its closest opposition, around its opposition in 2025, and at its farthest opposition. Also shown is how Mars appears when it’s most distant from the Earth at solar conjunction. Image via Dominic Ford/ In-The-Sky.org. Used with permission.
Sometimes, Mars is bright
Mars’ dramatic swings in brightness (and its red color) are why the early stargazers named Mars for their god of war.
Sometimes the war god rests. And sometimes he grows fierce! These changes are part of the reason Mars is so fascinating to watch in the night sky.
When Mars passes opposition, every 2 years, it appears large and bright for only a few weeks. The panel above shows the change in Mars’ apparent size from November 20, 2024, to March 12, 2025. Mars will appear 14.6 arcseconds wide on January 15, 2025. Image via Dominic Ford/ In-The-Sky.org. Used with permission.As Mars races towards its next opposition in January 2025, it’ll grow in apparent size and increase in brightness. Chart via Guy Ottewell’s 2024 Astronomical Calendar. Used with permission.
To understand why Mars varies so much in brightness in Earth’s sky, first realize that it isn’t a very big world. It’s only 4,219 miles (6,790 km) in diameter, making it only slightly more than half Earth’s size (7,922 miles or 12,750 km in diameter).
On the other hand, consider Mars in contrast to Jupiter, the biggest planet in our solar system. Jupiter is 86,881 miles (140,000 km) in diameter. As an illustration, more than 20 planets the size of Mars could be lined up side by side in front of Jupiter. Basically, Jupiter always looks bright, because it’s so big.
Not so for little Mars, however. Rather, its extremes in brightness have to do with its nearness (or lack of nearness) to Earth.
Mars isn’t very big, so its brightness – when it is bright – isn’t due to its bigness, as is true of Jupiter. Mars’ brightness, or lack of brightness, is all about how close we are to the red planet. It’s all about where Earth and Mars are, relative to each other, in their respective orbits around the sun. Image via NASA.
Future Martian oppositions
As mentioned above, the next opposition of Mars – when will appear at its brightest in Earth’s sky for that two-year period – will be January 2025. Check out the chart at C. Seligman’s Mars oppositions page that lists all oppositions of Mars from 1995 to 2037.
There’s a 15-year cycle of Mars, whereby the red planet is brighter and fainter at opposition. In July 2018, we were at the peak of the 2-year cycle – and the peak of the 15-year cycle – and Mars was very, very bright! In 2020, we were also at the peak of the 2-year cycle; however, Earth and Mars were farther apart at Mars’ opposition than they were in 2018. Still, 2020’s opposition of Mars was excellent. And, in December 2022, Mars had a good opposition but appeared smaller and dimmer than in 2020, since we were farther away from it. And the January 2025 opposition will find Mars smaller and dimmer than Mars was in 2022. Diagram by Roy L. Bishop. Copyright Royal Astronomical Society of Canada. Used with permission. Visit the RASC eStore to purchase the Observer’s Handbook, a necessary tool for all skywatchers.
EarthSky Community Photos
View at EarthSky Community Photos. | Paolo Bardelli of Italy made this composite image and said: “On January 16, 2025, Mars will be in opposition, the previous one occurred on December 8, 2022, when it became the brightest object in the night sky. During these periods, tracing the apparent motion of the red planet from evening to evening is very interesting, as a real ‘noose’ is created, with a double reversal of its movement. This put ancient sky observers in crisis at the time when the geocentric theory was dominant. Putting things in their place, it turned out to be a simple perspective effect, due to the mutual motion of Earth and Mars. This image is the sum of a sequence taken every useful evening, clouds permitting, from August 12, 2022, to March 22, 2023. The background is the sum of 22 shots of the area of the sky where Mars was located, the rich star field of the constellation del Toro (Taurus). By coincidence, in February 2023 the path of comet C/2022 E3 (ZTF) crossed the noose.” Thank you, Paolo!View at EarthSky Community Photos. | Miguel Ventura in Fafe, Portugal, captured this image on August 28, 2022, and wrote: “Every now and then and in addition to its natural beauty, the night sky and the whims of the universe offer us moments like this. With some planning and luck in the mix (truce from the clouds) I was able to photograph this magnificent alignment. We can see the Pleiades and the constellation of Taurus with the planet Mars between these 2 … below near the horizon the imposing constellation of Orion appears, announcing the autumn sky.” Thank you, Miguel!
Seeing red
Mars appears as a reddish light in the sky and, therefore, is often called the red planet. Other obvious red dots in the sky are reddish-orange Aldebaran and the famous red supergiant Betelgeuse. So, it is fun to contrast Mars’ color and intensity of red with that of Aldebaran or Betelgeuse.
And then there is red Antares. Antares is Greek for rival of Ares (Ares being the Greek name for Mars). Antares is sometimes said to be the anti-Mars due to its competing red color. For a few months every couple of years Mars is much brighter than Antares. Also, every couple of years Mars passes near Antares, as if taunting the star. Mars moves rapidly through the heavens and Antares is fixed to the starry firmament.
What makes them red?
Surface temperature is what determines the colors of the stars. The hottest stars are blue and the coolest stars are red. In fact, from hottest to coolest, the colors of stars range from blue, white, yellow, orange and red. And while the colors of stars might be hard to detect, some stars – like Aldebaran, Antares and Betelgeuse – are noticeably colorful.
On the other hand, Mars appears red for a different reason. It’s red because of iron oxide in the dust that covers this desert world. Iron oxide gives rust and blood its red color. Rovers on Mars sampled the Martian dust and determined it contains three colors: reds, browns and oranges. So those three colors are what you may see when you gaze upon Mars.
Do you see red when you look at Mars, Aldebaran, Antares and Betelgeuse? Are they the same color? Do you see any other colors of stars?
Bottom line: Mars was the bright red “star” near last night’s moon. Earth is racing up behind Mars in orbit now, about to catch up with it, bringing Mars to opposition in January 2025.
Sundial at Adler Planetarium in Chicago. A sundial can be used to measure the interval from one solar noon to the next. Earth’s longest days, from noon to noon, happen in December. Image via Wikimedia Commons/ CC BY-SA 4.0.
What is a day? You might casually talk about a day as a period of daylight. Or you could measure a day in relationship to the sun or the stars. Astronomers use the term solar day to describe a day relative to the sun. A solar day is the time from one solar noon – one local noon or high noon – to the next. It’s the interval between successive days as marked by the sun’s highest point in our sky. If you look at a day in that way, you can say that the longest days of the year come each year around the December solstice … no matter where you live on the globe.
What? Isn’t the shortest day for the Northern Hemisphere at the December solstice? Yes, it is, if we are talking about the period of daylight.
But, we’re talking about the (approximately) 24-hour interval from one solar noon to the next. In December, a day – one rotation of Earth relative to the noonday sun – is about half a minute longer than the average 24 hours, for the entire globe.
Keep in mind that the clocks on our walls don’t measure the true length of a day, as measured from solar noon to solar noon. To measure that sort of day, you’d need a sundial. A sundial will tell you the precise moment of local solar noon, when the sun reaches its highest point in the sky each day.
Days are always longer – as measured from one solar noon to the next – than 24 hours around the solstices, and less than 24 hours around the equinoxes.
Why are the days longer in December?
The days are at their longest now – for the entire globe – because we’re closer to the sun on the December solstice than we are at the June solstice. Earth’s perihelion – closest point to the sun – always comes in early January. So when we’re closest to the sun, our planet is moving a little faster than average in its orbit. That means our planet is traveling through space a little farther than average each day.
The result is that Earth has to rotate a little more on its axis for the sun to return to its noontime position. That effect lengthens the solar day by about eight seconds. In contrast, at aphelion, when the Earth is moving slower in its orbit, the solar day is about seven seconds shorter.
There’s another effect that happens during both the winter and summer solstices that increases the solar day by 21 seconds. It’s due to the way the sun moves mostly eastward, in relation to the stars, during solstices. Therefore, when the sun rises and moves up in the sky, it takes a bit longer to reach high noon from the previous day’s high noon.
For the winter solstice, the combined effects of these two phenomena increase the solar day by about 29 seconds.
Half a minute longer doesn’t sound like much, but the difference adds up. For instance, two weeks before the December solstice, noontime comes about seven minutes earlier by the clock than on the December solstice. And then two weeks after the December solstice, noon comes about seven minutes later by the clock than on the December solstice itself.
Sunrises and sunsets
Because the clock and sun are most out of sync right now, some befuddling phenomena cause people to scratch their heads at this time of the year. In the Northern Hemisphere, the year’s earliest sunsets precede the December winter solstice. And the year’s latest sunrises come after the December winter solstice. So the earliest sunsets came earlier in December for most of us; and the latest sunrises won’t come until early January.
In the Southern Hemisphere, the year’s earliest sunrises precede the December summer solstice, and the year’s latest sunsets come after the December summer solstice.
The fact that we’re closest to the sun in early January also means that Northern Hemisphere winter (Southern Hemisphere summer) is the shortest of the four seasons. Read more about the shortest season here.
However, at the same time … It’s the season of bountifully long solar days.
Visit Sunrise Sunset Calendars to find out the clock time for solar noon at your locality; remember to check the Solar noon box.
View larger. | This figure-8 shape is called an analemma. It shows the position of the sun at the same time each day, on successive days of a year. Read about analemmas at Wikipedia. Image via Matthew Chin in Hong Kong. Used with permission.
Bottom line: As measured from one solar noon to the next, December has the longest days – the longest interval from the sun’s highest point on one day to its highest point on the next day – for the entire Earth. And that’s true, no matter where you live on the globe.
Sundial at Adler Planetarium in Chicago. A sundial can be used to measure the interval from one solar noon to the next. Earth’s longest days, from noon to noon, happen in December. Image via Wikimedia Commons/ CC BY-SA 4.0.
What is a day? You might casually talk about a day as a period of daylight. Or you could measure a day in relationship to the sun or the stars. Astronomers use the term solar day to describe a day relative to the sun. A solar day is the time from one solar noon – one local noon or high noon – to the next. It’s the interval between successive days as marked by the sun’s highest point in our sky. If you look at a day in that way, you can say that the longest days of the year come each year around the December solstice … no matter where you live on the globe.
What? Isn’t the shortest day for the Northern Hemisphere at the December solstice? Yes, it is, if we are talking about the period of daylight.
But, we’re talking about the (approximately) 24-hour interval from one solar noon to the next. In December, a day – one rotation of Earth relative to the noonday sun – is about half a minute longer than the average 24 hours, for the entire globe.
Keep in mind that the clocks on our walls don’t measure the true length of a day, as measured from solar noon to solar noon. To measure that sort of day, you’d need a sundial. A sundial will tell you the precise moment of local solar noon, when the sun reaches its highest point in the sky each day.
Days are always longer – as measured from one solar noon to the next – than 24 hours around the solstices, and less than 24 hours around the equinoxes.
Why are the days longer in December?
The days are at their longest now – for the entire globe – because we’re closer to the sun on the December solstice than we are at the June solstice. Earth’s perihelion – closest point to the sun – always comes in early January. So when we’re closest to the sun, our planet is moving a little faster than average in its orbit. That means our planet is traveling through space a little farther than average each day.
The result is that Earth has to rotate a little more on its axis for the sun to return to its noontime position. That effect lengthens the solar day by about eight seconds. In contrast, at aphelion, when the Earth is moving slower in its orbit, the solar day is about seven seconds shorter.
There’s another effect that happens during both the winter and summer solstices that increases the solar day by 21 seconds. It’s due to the way the sun moves mostly eastward, in relation to the stars, during solstices. Therefore, when the sun rises and moves up in the sky, it takes a bit longer to reach high noon from the previous day’s high noon.
For the winter solstice, the combined effects of these two phenomena increase the solar day by about 29 seconds.
Half a minute longer doesn’t sound like much, but the difference adds up. For instance, two weeks before the December solstice, noontime comes about seven minutes earlier by the clock than on the December solstice. And then two weeks after the December solstice, noon comes about seven minutes later by the clock than on the December solstice itself.
Sunrises and sunsets
Because the clock and sun are most out of sync right now, some befuddling phenomena cause people to scratch their heads at this time of the year. In the Northern Hemisphere, the year’s earliest sunsets precede the December winter solstice. And the year’s latest sunrises come after the December winter solstice. So the earliest sunsets came earlier in December for most of us; and the latest sunrises won’t come until early January.
In the Southern Hemisphere, the year’s earliest sunrises precede the December summer solstice, and the year’s latest sunsets come after the December summer solstice.
The fact that we’re closest to the sun in early January also means that Northern Hemisphere winter (Southern Hemisphere summer) is the shortest of the four seasons. Read more about the shortest season here.
However, at the same time … It’s the season of bountifully long solar days.
Visit Sunrise Sunset Calendars to find out the clock time for solar noon at your locality; remember to check the Solar noon box.
View larger. | This figure-8 shape is called an analemma. It shows the position of the sun at the same time each day, on successive days of a year. Read about analemmas at Wikipedia. Image via Matthew Chin in Hong Kong. Used with permission.
Bottom line: As measured from one solar noon to the next, December has the longest days – the longest interval from the sun’s highest point on one day to its highest point on the next day – for the entire Earth. And that’s true, no matter where you live on the globe.
Artist’s concept of Eta Carinae’s Great Eruption in 1843. This star underwent a great eruption but not a full-blown supernova. Is it possible to catch a supernova before it happens? Image via Hubblesite.
How do we know if a star is about to go supernova? Some stars give no warning while others have slowly brightened or flickered before exploding.
Not all stars erupt in a true supernova. Other stars, like Eta Carinae, have great eruptions that don’t blow themselves entirely apart.
Stars in multiple star systems might interact with each other in a way that lets astronomers know that one of the stars is about to explode. The Vera C. Rubin Observatory will help search for supernova precursors, so astronomers can catch more stars in the act of erupting.
How to catch a supernova explosion before it happens
Stars are born, live and die in spectacular ways, with their deaths marked by one of the biggest known explosions in the universe. Like a campfire needs wood to keep burning, a star relies on nuclear fusion – primarily using hydrogen as fuel – to generate energy and counteract the crushing force of its own gravity.
But when the fuel runs out, the outward pressure vanishes, and the star collapses under its own weight. It falls inward at nearly the speed of light, crashing into the core and rebounding outward. Within seconds, the star violently blows itself apart. It hurls stellar debris into space at speeds thousands of times faster than the most powerful rocket ever built. This is a supernova explosion.
Astronomers aim to understand what types of stars produce different kinds of explosions. Do more massive stars result in brighter explosions? What happens if a star is surrounded by dust and gas when it explodes?
Finding a star that’s ready to blow
While we have simulations modeling a star’s death, they are difficult to validate. Observing a star’s behavior in real-time before the explosion could help answer these questions … but finding such a star is no easy task.
Scientists already do this with eruptions on Earth. Volcanologists monitor volcanoes, measuring changes in activity to predict an upcoming eruption. For example, in March 1980, Mount St. Helens in the U.S. began to show some precursor events, such as seismic activity, and dozens of steam eruptions ejecting ash and gas into the atmosphere.
Two months later, an earthquake triggered the largest landslide ever recorded, releasing built-up pressure in the magma chamber, resulting in a catastrophic eruption that devastated an area of over 230 square miles (600 square km).
Plumes of steam, gas, and ash often occurred at Mount St. Helens in the early 1980s. Image via USGS/ Wikipedia (public domain).
Pre-supernova eruptions
Massive stars – larger than around 10 times the mass of the sun – can do the same thing, albeit at much larger scales. In 2009, astronomers observed a bright event 65 million light-years away that on first impression resembled a supernova explosion.
Dubbed SN 2009ip, the explosion did not brighten as expected. Scientists reclassified it shortly after discovery as a “supernova impostor,” a giant eruption which ultimately does not destroy the star.
Over the next three years, the star underwent many rapid “flickering” events, a bit like quickly turning on and off a light bulb. Finally, in 2012, an unexpected supernova occurred. Scientists are still studying the evolution of the supernova explosion to this day. And what exactly happened from 2009 to 2012 remains a mystery.
Our team published a recent paper in Astronomy and Astrophysics about a peculiar star in the Virgo Cluster, coincidentally also 65 million light-years away. Unlike SN 2009ip, the star lacked hydrogen and consisted primarily of helium. The star slowly increased its brightness for over five years – akin to slowly turning on a bulb using a dimmer switch – before it went supernova.
That supernova, SN 2023fyq, provided astronomers with a rare opportunity. Observatories worldwide and in space captured the first light from the supernova explosion, known as shock breakout, largely due to the daily monitoring of the precursor activity.
Multiple stars and supernovas
This precursor activity offers an exciting chance to uncover the mysteries of supernova explosions, shedding light on both the conditions leading up to and following these cosmic events.
The underlying cause of this pre-supernova activity remains unclear. Scientists think an isolated massive star does not experience such rapid fluctuations in brightness. In the final moments of a star’s life, its core undergoes rapid evolution, desperately attempting to counteract the crushing force of gravity with its dwindling fuel reserves.
However, the star is so large at this stage that any activity in the core doesn’t have enough time to reach the surface. Observing these dramatic changes, occurring so close to the star’s demise, present a significant challenge to current theories.
One compelling hypothesis points to the interaction of multiple stars. Stars are born in dense clouds of gas and dust where multiple stars can form in close proximity. Neighboring stars may interact gravitationally with one another, exchanging material as they orbit each other.
This mass transfer could account for the changes in brightness observed in SN 2009ip before its explosion and the hydrogen deficiency we saw in SN 2023fyq. The companion involved might be another massive star, or perhaps a more exotic object, such as a black hole.
We know not all eruptions will not end in a supernova explosion. For example, in the 1840s, Eta Carinae – a star 100 times larger than the sun – experienced the Great Eruption. It launched 30 times the sun’s mass into space. Although this was an extremely energetic explosion, the massive star was not destroyed.
Watching for signals of a supernova
Do all stars announce their departure? We aren’t sure. We have observed seemingly normal supernovas with precursor eruptions, thanks in part to deep observations catching the faint precursor activity.
In 2025, the Vera C. Rubin Observatory, equipped with the world’s largest camera, will begin to study these events. At 3,200 megapixels, it is over 40 times more sensitive than cameras we have available on Earth. The observatory provides us the opportunity to search for fainter precursor activity.
At Stockholm University, our team is currently using telescopes from the European Southern Observatory and the Zwicky Transient Facility. This includes the Nordic Optical Telescope in La Palma, Spain, and the Very Large Telescope at Cerro Paranal in the Atacama Desert of northern Chile. We use them to identify the signs that indicate a star is nearing the end of its life.
By recognizing these signals, we can alert the scientific community and be ready to watch as a star experiences its final, dramatic moments.
Bottom line: Astronomers are looking for signals that a star is about to go supernova. Some stars give no warning while others have slowly brightened before exploding. The new Vera C. Rubin Observatory coming online will aid in the search.
Artist’s concept of Eta Carinae’s Great Eruption in 1843. This star underwent a great eruption but not a full-blown supernova. Is it possible to catch a supernova before it happens? Image via Hubblesite.
How do we know if a star is about to go supernova? Some stars give no warning while others have slowly brightened or flickered before exploding.
Not all stars erupt in a true supernova. Other stars, like Eta Carinae, have great eruptions that don’t blow themselves entirely apart.
Stars in multiple star systems might interact with each other in a way that lets astronomers know that one of the stars is about to explode. The Vera C. Rubin Observatory will help search for supernova precursors, so astronomers can catch more stars in the act of erupting.
How to catch a supernova explosion before it happens
Stars are born, live and die in spectacular ways, with their deaths marked by one of the biggest known explosions in the universe. Like a campfire needs wood to keep burning, a star relies on nuclear fusion – primarily using hydrogen as fuel – to generate energy and counteract the crushing force of its own gravity.
But when the fuel runs out, the outward pressure vanishes, and the star collapses under its own weight. It falls inward at nearly the speed of light, crashing into the core and rebounding outward. Within seconds, the star violently blows itself apart. It hurls stellar debris into space at speeds thousands of times faster than the most powerful rocket ever built. This is a supernova explosion.
Astronomers aim to understand what types of stars produce different kinds of explosions. Do more massive stars result in brighter explosions? What happens if a star is surrounded by dust and gas when it explodes?
Finding a star that’s ready to blow
While we have simulations modeling a star’s death, they are difficult to validate. Observing a star’s behavior in real-time before the explosion could help answer these questions … but finding such a star is no easy task.
Scientists already do this with eruptions on Earth. Volcanologists monitor volcanoes, measuring changes in activity to predict an upcoming eruption. For example, in March 1980, Mount St. Helens in the U.S. began to show some precursor events, such as seismic activity, and dozens of steam eruptions ejecting ash and gas into the atmosphere.
Two months later, an earthquake triggered the largest landslide ever recorded, releasing built-up pressure in the magma chamber, resulting in a catastrophic eruption that devastated an area of over 230 square miles (600 square km).
Plumes of steam, gas, and ash often occurred at Mount St. Helens in the early 1980s. Image via USGS/ Wikipedia (public domain).
Pre-supernova eruptions
Massive stars – larger than around 10 times the mass of the sun – can do the same thing, albeit at much larger scales. In 2009, astronomers observed a bright event 65 million light-years away that on first impression resembled a supernova explosion.
Dubbed SN 2009ip, the explosion did not brighten as expected. Scientists reclassified it shortly after discovery as a “supernova impostor,” a giant eruption which ultimately does not destroy the star.
Over the next three years, the star underwent many rapid “flickering” events, a bit like quickly turning on and off a light bulb. Finally, in 2012, an unexpected supernova occurred. Scientists are still studying the evolution of the supernova explosion to this day. And what exactly happened from 2009 to 2012 remains a mystery.
Our team published a recent paper in Astronomy and Astrophysics about a peculiar star in the Virgo Cluster, coincidentally also 65 million light-years away. Unlike SN 2009ip, the star lacked hydrogen and consisted primarily of helium. The star slowly increased its brightness for over five years – akin to slowly turning on a bulb using a dimmer switch – before it went supernova.
That supernova, SN 2023fyq, provided astronomers with a rare opportunity. Observatories worldwide and in space captured the first light from the supernova explosion, known as shock breakout, largely due to the daily monitoring of the precursor activity.
Multiple stars and supernovas
This precursor activity offers an exciting chance to uncover the mysteries of supernova explosions, shedding light on both the conditions leading up to and following these cosmic events.
The underlying cause of this pre-supernova activity remains unclear. Scientists think an isolated massive star does not experience such rapid fluctuations in brightness. In the final moments of a star’s life, its core undergoes rapid evolution, desperately attempting to counteract the crushing force of gravity with its dwindling fuel reserves.
However, the star is so large at this stage that any activity in the core doesn’t have enough time to reach the surface. Observing these dramatic changes, occurring so close to the star’s demise, present a significant challenge to current theories.
One compelling hypothesis points to the interaction of multiple stars. Stars are born in dense clouds of gas and dust where multiple stars can form in close proximity. Neighboring stars may interact gravitationally with one another, exchanging material as they orbit each other.
This mass transfer could account for the changes in brightness observed in SN 2009ip before its explosion and the hydrogen deficiency we saw in SN 2023fyq. The companion involved might be another massive star, or perhaps a more exotic object, such as a black hole.
We know not all eruptions will not end in a supernova explosion. For example, in the 1840s, Eta Carinae – a star 100 times larger than the sun – experienced the Great Eruption. It launched 30 times the sun’s mass into space. Although this was an extremely energetic explosion, the massive star was not destroyed.
Watching for signals of a supernova
Do all stars announce their departure? We aren’t sure. We have observed seemingly normal supernovas with precursor eruptions, thanks in part to deep observations catching the faint precursor activity.
In 2025, the Vera C. Rubin Observatory, equipped with the world’s largest camera, will begin to study these events. At 3,200 megapixels, it is over 40 times more sensitive than cameras we have available on Earth. The observatory provides us the opportunity to search for fainter precursor activity.
At Stockholm University, our team is currently using telescopes from the European Southern Observatory and the Zwicky Transient Facility. This includes the Nordic Optical Telescope in La Palma, Spain, and the Very Large Telescope at Cerro Paranal in the Atacama Desert of northern Chile. We use them to identify the signs that indicate a star is nearing the end of its life.
By recognizing these signals, we can alert the scientific community and be ready to watch as a star experiences its final, dramatic moments.
Bottom line: Astronomers are looking for signals that a star is about to go supernova. Some stars give no warning while others have slowly brightened before exploding. The new Vera C. Rubin Observatory coming online will aid in the search.
In 2024, the December solstice falls at 9:21 UTC on December 21 (3:21 a.m. CST). Long nights, short days, for the Northern Hemisphere. Short nights, long days, for our friends south of the equator. No matter where you live on Earth’s globe, the solstice is your signal to celebrate seasonal change.
The December solstice marks the sun’s southernmost point in the sky, for all of Earth, for this year. It comes at 9:21 UTC (3:21 a.m. CST) on December 21. Though no world body has decreed it, we in the Northern Hemisphere will celebrate the first day of winter at this solstice. For us, it heralds the longest nights and shortest days of our year.
Meanwhile, people in the Southern Hemisphere will celebrate the first day of summer at this solstice. For them it marks the shortest nights and longest days.
After this solstice, the sun will begin moving northward in the sky again. It’s fun to track the northward movement of the sunsets on your horizon with pieces of tape on a window, or just by noticing the shifting sunset point from your favorite spot to observe.
View larger. | Ian Hennes in Medicine Hat, Alberta, Canada, created this solargram between a June solstice and a December solstice. It shows the path of the sun during that time period. Thank you, Ian! Used with permission.View at EarthSky Community Photos.| José Palma in Mina São Domingos, Portugal, shared this solargram. He wrote: “The objective of this ultra-long exposure was to show in a single image the variation of the path of the sun and its altitude, between the summer solstice and the winter solstice, resulting in 183 days – 4,392 hours – of exposure.” Read more about this image. Thank you, José.
What is a solstice?
The earliest people on Earth knew that the sun’s path across the sky, the length of daylight, and the location of the sunrise and sunset all shifted in a regular way throughout the year. They built monuments such as Stonehenge in England and at Machu Picchu in Peru to follow the sun’s yearly progress.
Today, we picture the solstice from the vantage point of space, and we know that the solstice is an astronomical event. It’s caused by the tilt of Earth’s axis and by its orbital motion around the sun.
Earth doesn’t orbit upright. Instead, it’s tilted on its axis by 23.5 degrees. Through the year, this tilt causes Earth’s Northern and Southern Hemispheres to trade places in receiving the sun’s light and warmth most directly. It’s this tilt, not our distance from the sun, that causes winter and summer.
In fact, we’re closest to – not farthest from – the sun at the turn of every new year. At the same time, we in the Northern Hemisphere are moving into winter. That’s because the Northern Hemisphere leans farthest away from the sun for the year around this time.
On the day of the December solstice, the sun takes its farthest pass south on the globe. Image via Jecowa/ Wikimedia Commons (CC BY-SA 3.0).
Why isn’t the earliest sunset on the shortest day?
The December solstice marks the shortest day of the year in the Northern Hemisphere and longest day in the Southern Hemisphere. But the earliest sunset – or earliest sunrise if you’re south of the equator – happens before the December solstice.
Instead of focusing on the time of sunset or sunrise, the key is in what is called true solar noon, which is the time of day that the sun reaches its highest point in its journey across your sky.
In early December, true solar noon comes nearly 10 minutes earlier by the clock than it does at the solstice around December 21. With true noon coming later on the solstice, so will the sunrise and sunset times.
It’s this discrepancy between clock time and sun time that causes the Northern Hemisphere’s earliest sunset and the Southern Hemisphere’s earliest sunrise to precede the December solstice.
The precise date of the earliest sunset (or earliest sunrise) depends on your latitude. But the sequence is always the same: earliest sunset, shortest day at the solstice, latest sunrise around early January. Or, for the Southern Hemisphere now, earliest sunrise, longest day at the solstice, latest sunset around early July.
And so the cycle continues.
View at EarthSky Community Photos. | Karl Diefenderfer of Quakertown, Pennsylvania, wrote: “Vibrant winter’s solstice sunrise.” Thank you, Karl! By the way, the December solstice starts the year’s shortest season.
The poles at the December solstice
At the December solstice, Earth is positioned so the sun stays below the North Pole’s horizon. Meanwhile, the sun is up 24 hours a day at the South Pole.
All locations south of the equator have day lengths greater than 12 hours.
All locations north of the equator have day lengths shorter than 12 hours.
Where should I look to see signs of the December solstice in nature?
Everywhere.
For all of Earth’s creatures, nothing is so fundamental as the length of daylight. After all, the sun is the ultimate source of all light and warmth on Earth.
In the Northern Hemisphere, you’ll notice late dawns and early sunsets, the low arc of the sun across the sky each day, and how low the sun appears in the sky at local noon. Look at your noontime shadow, too. Around the time of the December solstice, it’s your longest noontime shadow of the year.
In the Southern Hemisphere, it’s opposite. Dawn comes early, dusk comes late, the sun is high, and it’s your shortest noontime shadow of the year.
Bottom line: The 2024 December solstice takes place on December 21, at 9:21 UTC. It marks the Northern Hemisphere’s shortest day (first day of winter) and Southern Hemisphere’s longest day (first day of summer). Happy solstice to all!
In 2024, the December solstice falls at 9:21 UTC on December 21 (3:21 a.m. CST). Long nights, short days, for the Northern Hemisphere. Short nights, long days, for our friends south of the equator. No matter where you live on Earth’s globe, the solstice is your signal to celebrate seasonal change.
The December solstice marks the sun’s southernmost point in the sky, for all of Earth, for this year. It comes at 9:21 UTC (3:21 a.m. CST) on December 21. Though no world body has decreed it, we in the Northern Hemisphere will celebrate the first day of winter at this solstice. For us, it heralds the longest nights and shortest days of our year.
Meanwhile, people in the Southern Hemisphere will celebrate the first day of summer at this solstice. For them it marks the shortest nights and longest days.
After this solstice, the sun will begin moving northward in the sky again. It’s fun to track the northward movement of the sunsets on your horizon with pieces of tape on a window, or just by noticing the shifting sunset point from your favorite spot to observe.
View larger. | Ian Hennes in Medicine Hat, Alberta, Canada, created this solargram between a June solstice and a December solstice. It shows the path of the sun during that time period. Thank you, Ian! Used with permission.View at EarthSky Community Photos.| José Palma in Mina São Domingos, Portugal, shared this solargram. He wrote: “The objective of this ultra-long exposure was to show in a single image the variation of the path of the sun and its altitude, between the summer solstice and the winter solstice, resulting in 183 days – 4,392 hours – of exposure.” Read more about this image. Thank you, José.
What is a solstice?
The earliest people on Earth knew that the sun’s path across the sky, the length of daylight, and the location of the sunrise and sunset all shifted in a regular way throughout the year. They built monuments such as Stonehenge in England and at Machu Picchu in Peru to follow the sun’s yearly progress.
Today, we picture the solstice from the vantage point of space, and we know that the solstice is an astronomical event. It’s caused by the tilt of Earth’s axis and by its orbital motion around the sun.
Earth doesn’t orbit upright. Instead, it’s tilted on its axis by 23.5 degrees. Through the year, this tilt causes Earth’s Northern and Southern Hemispheres to trade places in receiving the sun’s light and warmth most directly. It’s this tilt, not our distance from the sun, that causes winter and summer.
In fact, we’re closest to – not farthest from – the sun at the turn of every new year. At the same time, we in the Northern Hemisphere are moving into winter. That’s because the Northern Hemisphere leans farthest away from the sun for the year around this time.
On the day of the December solstice, the sun takes its farthest pass south on the globe. Image via Jecowa/ Wikimedia Commons (CC BY-SA 3.0).
Why isn’t the earliest sunset on the shortest day?
The December solstice marks the shortest day of the year in the Northern Hemisphere and longest day in the Southern Hemisphere. But the earliest sunset – or earliest sunrise if you’re south of the equator – happens before the December solstice.
Instead of focusing on the time of sunset or sunrise, the key is in what is called true solar noon, which is the time of day that the sun reaches its highest point in its journey across your sky.
In early December, true solar noon comes nearly 10 minutes earlier by the clock than it does at the solstice around December 21. With true noon coming later on the solstice, so will the sunrise and sunset times.
It’s this discrepancy between clock time and sun time that causes the Northern Hemisphere’s earliest sunset and the Southern Hemisphere’s earliest sunrise to precede the December solstice.
The precise date of the earliest sunset (or earliest sunrise) depends on your latitude. But the sequence is always the same: earliest sunset, shortest day at the solstice, latest sunrise around early January. Or, for the Southern Hemisphere now, earliest sunrise, longest day at the solstice, latest sunset around early July.
And so the cycle continues.
View at EarthSky Community Photos. | Karl Diefenderfer of Quakertown, Pennsylvania, wrote: “Vibrant winter’s solstice sunrise.” Thank you, Karl! By the way, the December solstice starts the year’s shortest season.
The poles at the December solstice
At the December solstice, Earth is positioned so the sun stays below the North Pole’s horizon. Meanwhile, the sun is up 24 hours a day at the South Pole.
All locations south of the equator have day lengths greater than 12 hours.
All locations north of the equator have day lengths shorter than 12 hours.
Where should I look to see signs of the December solstice in nature?
Everywhere.
For all of Earth’s creatures, nothing is so fundamental as the length of daylight. After all, the sun is the ultimate source of all light and warmth on Earth.
In the Northern Hemisphere, you’ll notice late dawns and early sunsets, the low arc of the sun across the sky each day, and how low the sun appears in the sky at local noon. Look at your noontime shadow, too. Around the time of the December solstice, it’s your longest noontime shadow of the year.
In the Southern Hemisphere, it’s opposite. Dawn comes early, dusk comes late, the sun is high, and it’s your shortest noontime shadow of the year.
Bottom line: The 2024 December solstice takes place on December 21, at 9:21 UTC. It marks the Northern Hemisphere’s shortest day (first day of winter) and Southern Hemisphere’s longest day (first day of summer). Happy solstice to all!
View at EarthSky Community Photos. | Peter Lowenstein caught the daytime moon in its waning gibbous phase from Mutare, Zimbabwe. He said: “Three-quarters of an hour after sunrise, I photographed the daytime moon descending toward the top of a flowering African Tulip (Spathodia campanulta) tree.” Thank you, Peter!
Watch for a daytime moon
This month’s full moon came early on December 15, 2024. So the moon is now in a waning gibbous phase, rising later and later each successive night.
And that means the moon is setting later and later now. It’s setting after sunrise. That’s why the mornings after a full moon are a good time to catch a nearly full daytime moon after sunrise, over your western horizon. Watch for it!
The moon is up in the daytime half of the time. But, because it’s pale against the blue sky, it’s not as noticeable during the day as at night. Still, there are certain windows each month during which the daytime moon is most noticeable.
The coming week presents one of those windows. It’s a good time to watch for a daytime moon.
December 17-18 overnight: Moon passes in front of Mars
The waning gibbous moon will lie close to the red planet Mars on the evening of December 17, 2024. At 9 UTC on the morning of December 18, 2024, the moon will occult – or pass in front of – Mars, visible from parts of Canada, Greenland, eastern Russia and Alaska and other locations. Others will see Mars close to the moon. Also nearby will be the twin stars of Gemini: Castor and Pollux. They’ll rise several hours after sunset and be visible through dawn. Read Mars updates for 2024, here.
Our charts are mostly set for the northern half of Earth. To see a precise view – and time – from your location, try Stellarium Online.
On the mornings of December 19 and 20, 2024, the waning gibbous moon will float near the star Regulus, the brightest star in Leo the Lion. Regulus is the punctuation mark at the bottom of a pattern of stars called the Sickle. Look for them a few hours before dawn. Meet Regulus, Leo the Lion’s Heart.
View at EarthSky Community Photos. | Peter Lowenstein caught the daytime moon in its waning gibbous phase from Mutare, Zimbabwe. He said: “Three-quarters of an hour after sunrise, I photographed the daytime moon descending toward the top of a flowering African Tulip (Spathodia campanulta) tree.” Thank you, Peter!
Watch for a daytime moon
This month’s full moon came early on December 15, 2024. So the moon is now in a waning gibbous phase, rising later and later each successive night.
And that means the moon is setting later and later now. It’s setting after sunrise. That’s why the mornings after a full moon are a good time to catch a nearly full daytime moon after sunrise, over your western horizon. Watch for it!
The moon is up in the daytime half of the time. But, because it’s pale against the blue sky, it’s not as noticeable during the day as at night. Still, there are certain windows each month during which the daytime moon is most noticeable.
The coming week presents one of those windows. It’s a good time to watch for a daytime moon.
December 17-18 overnight: Moon passes in front of Mars
The waning gibbous moon will lie close to the red planet Mars on the evening of December 17, 2024. At 9 UTC on the morning of December 18, 2024, the moon will occult – or pass in front of – Mars, visible from parts of Canada, Greenland, eastern Russia and Alaska and other locations. Others will see Mars close to the moon. Also nearby will be the twin stars of Gemini: Castor and Pollux. They’ll rise several hours after sunset and be visible through dawn. Read Mars updates for 2024, here.
Our charts are mostly set for the northern half of Earth. To see a precise view – and time – from your location, try Stellarium Online.
On the mornings of December 19 and 20, 2024, the waning gibbous moon will float near the star Regulus, the brightest star in Leo the Lion. Regulus is the punctuation mark at the bottom of a pattern of stars called the Sickle. Look for them a few hours before dawn. Meet Regulus, Leo the Lion’s Heart.
