View larger/ full image. | This cropped view shows a few of the 34 dust devils captured in a single image of the Martian surface. The Mars Express orbiter captured the full view on December 7, 2024, and ESA shared it on June 17, 2026. To see all 34 dust devils, click through to this zoomable image from ESA. How many can you spot? Image via ESA/DLR/FU Berlin.
Mars is famous for its tornado-like whirlwinds, made of the dusty debris coating its surface. These are dust devils. They form the same way on Mars as they do on Earth: as the sun warms the ground, the ground then heats the thin layer of air above. Then that air rises quickly through the cooler, dense air above, spiraling around a small area of low pressure.
On June 17, 2026, ESA shared an image from its Mars Express orbiter of 34 dust devils it captured on the red planet’s surface back on December 7, 2024. Can you spot all the dust devils in the image above?
Look closely. This region of Mars is in a valley system known as Mamers Valles. It holds ridges and plateau-like areas along with many small craters. Although the dust devils may look tiny – as a small light-colored dot with a shadow – in reality, dust devils on Mars can grow even larger than those on Earth. Martian dust devils can tower up to 5 miles (8 km) high and span hundreds of yards wide.
The location of the dust devils is in the image at the bottom of this post.
View larger. | There are 34 dust devils on Mars in this 1 image. How many can you spot? A key is below. The Mars Express orbiter captured this view of Mars on December 7, 2024, and ESA shared it on June 17, 2026. Image via ESA/DLR/FU Berlin.
More on Mamers Valles
Mamers Valles lies in Mars’ northern hemisphere. It consists of of valleys and canyons, some of which stretch for more than 600 miles (1,000 km). The higher areas are mesas, cliffs and some debris-covered glaciers. The glaciers lie at the base of the steep slopes. The terrain shows evidence that it was carved by flowing materials, such as water, ice and lava, sometime in its past.
Mamers Valles is a large valley in Mars’ northern hemisphere. This false-color view shows the location of the dust-devil-filled image above, which ESA released on June 17, 2026. Image via NASA/USGS; ESA/DLR/FU Berlin.
Answer key for the dust devils
The white circles mark the locations of the 34 dust devils on Mars that the Mars Express orbiter spotted. Image via ESA/DLR/FU Berlin.
Bottom line: The Mars Express orbiter caught this view of the red planet, which is peppered with whirlwinds. Can you spot 34 dust devils in this one shot of Mars?
View larger/ full image. | This cropped view shows a few of the 34 dust devils captured in a single image of the Martian surface. The Mars Express orbiter captured the full view on December 7, 2024, and ESA shared it on June 17, 2026. To see all 34 dust devils, click through to this zoomable image from ESA. How many can you spot? Image via ESA/DLR/FU Berlin.
Mars is famous for its tornado-like whirlwinds, made of the dusty debris coating its surface. These are dust devils. They form the same way on Mars as they do on Earth: as the sun warms the ground, the ground then heats the thin layer of air above. Then that air rises quickly through the cooler, dense air above, spiraling around a small area of low pressure.
On June 17, 2026, ESA shared an image from its Mars Express orbiter of 34 dust devils it captured on the red planet’s surface back on December 7, 2024. Can you spot all the dust devils in the image above?
Look closely. This region of Mars is in a valley system known as Mamers Valles. It holds ridges and plateau-like areas along with many small craters. Although the dust devils may look tiny – as a small light-colored dot with a shadow – in reality, dust devils on Mars can grow even larger than those on Earth. Martian dust devils can tower up to 5 miles (8 km) high and span hundreds of yards wide.
The location of the dust devils is in the image at the bottom of this post.
View larger. | There are 34 dust devils on Mars in this 1 image. How many can you spot? A key is below. The Mars Express orbiter captured this view of Mars on December 7, 2024, and ESA shared it on June 17, 2026. Image via ESA/DLR/FU Berlin.
More on Mamers Valles
Mamers Valles lies in Mars’ northern hemisphere. It consists of of valleys and canyons, some of which stretch for more than 600 miles (1,000 km). The higher areas are mesas, cliffs and some debris-covered glaciers. The glaciers lie at the base of the steep slopes. The terrain shows evidence that it was carved by flowing materials, such as water, ice and lava, sometime in its past.
Mamers Valles is a large valley in Mars’ northern hemisphere. This false-color view shows the location of the dust-devil-filled image above, which ESA released on June 17, 2026. Image via NASA/USGS; ESA/DLR/FU Berlin.
Answer key for the dust devils
The white circles mark the locations of the 34 dust devils on Mars that the Mars Express orbiter spotted. Image via ESA/DLR/FU Berlin.
Bottom line: The Mars Express orbiter caught this view of the red planet, which is peppered with whirlwinds. Can you spot 34 dust devils in this one shot of Mars?
View at EarthSky Community Photos. | Christy Mandeville in Indian Shores, Florida, captured this dramatic sunset on a June evening in 2022. Christy wrote: “The little boy in the photo kept running around me as I was trying to capture the perfect sunset photo. After I went through the hundreds of photos I captured, I had no idea that he was in any of them! This one stood out.” Thank you, Christy! Read below why the longest sunsets happen around the solstices.
Here’s a natural phenomenon you might not have imagined: the longest sunsets happen around the time of the solstices. That is, it takes more seconds for the body of the sun to sink below your western horizon around the solstices, and fewer seconds around the equinoxes. It’s true whether you live in Earth’s Northern or Southern Hemisphere.
As viewed from both the Northern and Southern Hemispheres, the sun rises and sets farthest north at the June solstice and farthest south at the December solstice.
Now consider that the farther the sun sets from due west along the horizon, the shallower the angle of the setting sun. That means a longer duration for sunset at the solstices.
Meanwhile, at an 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.
Longest sunsets are how long?
The sunset duration varies by latitude. But let’s just consider one latitude: 40 degrees north, which is the latitude of Denver or Philadelphia in the United States, Sardinia in the Mediterranean, or Beijing in China.
At that latitude, on the day of a solstice, the sun sets in about 3 minutes and 15 seconds.
That’s half a minute longer than the sunset at the same latitude on the day of an equinox. The equinox sun at 40 degrees north latitude sets in roughly 2 minutes and 45 seconds.
At more northerly temperate latitudes, the sunset duration is greater; and at latitudes closer to the equator, the sunset duration is less. Near the Arctic Circle (65 degrees north latitude), the duration of a solstice sunset lasts about 15 minutes. At the equator (0 degrees latitude), the solstice sun takes a little over 2 minutes and 15 seconds to set.
Regardless of latitude, however, the duration of sunset is always longest at or near the solstices.
The sunsets are longer in December than June
As it turns out, the sunset and sunrise are a tad longer on the December solstice than they are on the June solstice.
That’s because the sun is closer to Earth in December than it is in June. Therefore, the sun’s disk looms a bit larger in our sky in December, and so it takes slightly longer to set.
Additionally, the closer December sun moves eastward upon the ecliptic at a faster clip, helping to slow down the December solstice sunset (and sunrise) even more. For instance, at 50 degrees north latitude, the winter solstice sunset (sunrise) lasts about 4 minutes and 18 seconds, or about 8 seconds longer than the sunset (sunrise) on the summer solstice.
And now you know!
Equinoxes and solstices, via Geosync. The Earth’s axis points straight up and down, with north at the top. The solstices are on the left (December solstice at top, June solstice at bottom) and the equinoxes are to the right (March equinox at top, September equinox at bottom). Image via NASA.
Some sunsets from EarthSky Community Photos
View at EarthSky Community Photos. | Cecille Kennedy captured this sunset on May 11, 2026, from Oregon and wrote: “The sun is sinking into the ocean horizon and if you look close there’s a thin line of neon green on its top rim (precursor to the green flash though the flash didn’t happen). A brown pelican on the right is flying south. Typically they are seen flying north this time of year but sometimes they are seen flying south for a brief stop at their favorite designated spots then proceed to fly north.” Thank you, Cecille!View at EarthSky Community Photos. | Jelieta Walinski at Kitt Peak National Observatory near Tucson, Arizona, captured this solstice sunset on June 20, 2025. Jelieta wrote: “On the summer solstice, my husband and I ventured to Kitt Peak National Observatory, 6,000 feet above sea level, to witness the sun’s majesty. After scouting the perfect location, I was thrilled to capture the sun’s splendor with a unique twist — the elusive green flash!” Thank you, Jelieta!
Bottom line: Here’s a natural phenomenon you might never have imagined: the longest sunsets happen around the time of a solstice.
View at EarthSky Community Photos. | Christy Mandeville in Indian Shores, Florida, captured this dramatic sunset on a June evening in 2022. Christy wrote: “The little boy in the photo kept running around me as I was trying to capture the perfect sunset photo. After I went through the hundreds of photos I captured, I had no idea that he was in any of them! This one stood out.” Thank you, Christy! Read below why the longest sunsets happen around the solstices.
Here’s a natural phenomenon you might not have imagined: the longest sunsets happen around the time of the solstices. That is, it takes more seconds for the body of the sun to sink below your western horizon around the solstices, and fewer seconds around the equinoxes. It’s true whether you live in Earth’s Northern or Southern Hemisphere.
As viewed from both the Northern and Southern Hemispheres, the sun rises and sets farthest north at the June solstice and farthest south at the December solstice.
Now consider that the farther the sun sets from due west along the horizon, the shallower the angle of the setting sun. That means a longer duration for sunset at the solstices.
Meanwhile, at an 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.
Longest sunsets are how long?
The sunset duration varies by latitude. But let’s just consider one latitude: 40 degrees north, which is the latitude of Denver or Philadelphia in the United States, Sardinia in the Mediterranean, or Beijing in China.
At that latitude, on the day of a solstice, the sun sets in about 3 minutes and 15 seconds.
That’s half a minute longer than the sunset at the same latitude on the day of an equinox. The equinox sun at 40 degrees north latitude sets in roughly 2 minutes and 45 seconds.
At more northerly temperate latitudes, the sunset duration is greater; and at latitudes closer to the equator, the sunset duration is less. Near the Arctic Circle (65 degrees north latitude), the duration of a solstice sunset lasts about 15 minutes. At the equator (0 degrees latitude), the solstice sun takes a little over 2 minutes and 15 seconds to set.
Regardless of latitude, however, the duration of sunset is always longest at or near the solstices.
The sunsets are longer in December than June
As it turns out, the sunset and sunrise are a tad longer on the December solstice than they are on the June solstice.
That’s because the sun is closer to Earth in December than it is in June. Therefore, the sun’s disk looms a bit larger in our sky in December, and so it takes slightly longer to set.
Additionally, the closer December sun moves eastward upon the ecliptic at a faster clip, helping to slow down the December solstice sunset (and sunrise) even more. For instance, at 50 degrees north latitude, the winter solstice sunset (sunrise) lasts about 4 minutes and 18 seconds, or about 8 seconds longer than the sunset (sunrise) on the summer solstice.
And now you know!
Equinoxes and solstices, via Geosync. The Earth’s axis points straight up and down, with north at the top. The solstices are on the left (December solstice at top, June solstice at bottom) and the equinoxes are to the right (March equinox at top, September equinox at bottom). Image via NASA.
Some sunsets from EarthSky Community Photos
View at EarthSky Community Photos. | Cecille Kennedy captured this sunset on May 11, 2026, from Oregon and wrote: “The sun is sinking into the ocean horizon and if you look close there’s a thin line of neon green on its top rim (precursor to the green flash though the flash didn’t happen). A brown pelican on the right is flying south. Typically they are seen flying north this time of year but sometimes they are seen flying south for a brief stop at their favorite designated spots then proceed to fly north.” Thank you, Cecille!View at EarthSky Community Photos. | Jelieta Walinski at Kitt Peak National Observatory near Tucson, Arizona, captured this solstice sunset on June 20, 2025. Jelieta wrote: “On the summer solstice, my husband and I ventured to Kitt Peak National Observatory, 6,000 feet above sea level, to witness the sun’s majesty. After scouting the perfect location, I was thrilled to capture the sun’s splendor with a unique twist — the elusive green flash!” Thank you, Jelieta!
Bottom line: Here’s a natural phenomenon you might never have imagined: the longest sunsets happen around the time of a solstice.
View at EarthSky Community Photos. | The bright star in the center of this montage of time-exposure photos is Polaris, the North Star. Perhaps you’ve heard it stays still in the northern sky, while the other stars circle around it? That’s true to the unaided eye, but not to a timelapse camera. Marcella Giulia Pace in Modica, Sicily, Italy, made this comparison of star trails in late 2022 and throughout 2023. As you can see, Polaris does move in a tiny circle around celestial north. Beautiful work, Marcella! Thank you.
The North Star, aka Polaris
The North Star, also known as Polaris, appears to stay fixed in our northern sky. It marks the location of the sky’s north pole – the north celestial pole – which is the point around which the whole starry northern sky turns as the Earth rotates. That’s why you can always use Polaris to find the direction north.
But even though the North Star doesn’t appear to move, a timelapse video reveals that it actually does. It makes its own little circle around the sky’s north pole every day. That’s because the North Star is offset a little – about 0.65 degrees – from celestial north. So Polaris makes a circle that’s 1.3 degrees in diameter each day.
Why do stars move, anyway?
Why does Polaris – and all the other stars in the sky – move at all? The answer is Earth’s spin. Because Earth rotates counter-clockwise when looking from above the North Pole, the sun in the daytime – and most stars at night – appear to rise in the east and set in the west.
Depending on your latitude, certain stars will be close enough to your nearest pole that they never rise or set. Never dipping below the horizon, they instead circle above you constantly. These are called circumpolar stars.
And the North Star is a special example of a circumpolar star. Because it lies almost exactly above Earth’s northern axis, it’s like the hub of a wheel. It doesn’t rise or set, and barely moves in a circle. Instead, it appears – to the eye – to stay put in the northern sky.
How high in your sky?
The North Star not only points toward the north, but its height in the northern sky also matches your latitude on earth. If you are sailing the Caribbean at 16° north latitude, the North Star will be about 16° high in your sky. If you are sailing around Nova Scotia, at 44° north latitude, then the North Star will be about 44° high in your northern sky. Each degree north or south equals 69 miles (111 km), so traveling 690 miles north or south will change your latitude, and the North Star’s elevation, by 10 degrees.
The 26,000-year precession cycle causes the north celestial pole to move counter-clockwise relative to the background stars. Whichever star is closest to the north celestial pole is called the North Star. Image via Wikimedia Commons.
Taking turns as the North Star
A motion of Earth called precession causes our axis to trace out an imaginary circle on the celestial sphere every 26,000 years. And that means the star closest to the north celestial pole isn’t fixed.
Thousands of years ago, when the pyramids were rising from the sands of ancient Egypt, the North Star was an inconspicuous star called Thuban in the constellation Draco the Dragon.
Twelve thousand years from now, the blue-white star Vega in the constellation Lyra the Harp will be a much brighter North Star than our current Polaris.
Polaris could be a name for any North Star. Our current Polaris used to be called Phoenice. It is the 49th brightest star in the sky. It is not known for its brightness, but for its unique position in the sky.
View at EarthSky Community Photos. | Jeff Grubbs in Elgin, Arizona, captured these star trails on May 22, 2025. Thanks, Jeff! You can see all the stars circling around the star Polaris.
Proper motion
By the way, Polaris – like all stars – has more than one kind of motion. There’s the movement we see on our sky, caused by the Earth’s rotation. And then there’s each star’s actual motion through space.
The stars we see in our night sky are all members of our Milky Way galaxy. All of these stars are moving through space, but they’re so far away we can’t easily see them move. That’s why the stars appear fixed relative to each other. And it’s why, for the most part, we see the same constellations as our ancestors.
But over time, this movement – called proper motion – rearranges the patterns of stars we see in our sky. For Polaris, that movement is small, about 46 arcseconds in 1,000 years. That is about 1/40th of the diameter of the full moon as seen from Earth. So when you’re talking about stars moving or staying fixed, remember … they are all moving through the vastness of space. It’s just the relatively short time of a human lifespan that prevents us from seeing this grand motion.
Bottom line: The North Star is a symbol for constancy. But a video or star trails image reveals that it makes its own little circle around the sky’s north pole every day.
View at EarthSky Community Photos. | The bright star in the center of this montage of time-exposure photos is Polaris, the North Star. Perhaps you’ve heard it stays still in the northern sky, while the other stars circle around it? That’s true to the unaided eye, but not to a timelapse camera. Marcella Giulia Pace in Modica, Sicily, Italy, made this comparison of star trails in late 2022 and throughout 2023. As you can see, Polaris does move in a tiny circle around celestial north. Beautiful work, Marcella! Thank you.
The North Star, aka Polaris
The North Star, also known as Polaris, appears to stay fixed in our northern sky. It marks the location of the sky’s north pole – the north celestial pole – which is the point around which the whole starry northern sky turns as the Earth rotates. That’s why you can always use Polaris to find the direction north.
But even though the North Star doesn’t appear to move, a timelapse video reveals that it actually does. It makes its own little circle around the sky’s north pole every day. That’s because the North Star is offset a little – about 0.65 degrees – from celestial north. So Polaris makes a circle that’s 1.3 degrees in diameter each day.
Why do stars move, anyway?
Why does Polaris – and all the other stars in the sky – move at all? The answer is Earth’s spin. Because Earth rotates counter-clockwise when looking from above the North Pole, the sun in the daytime – and most stars at night – appear to rise in the east and set in the west.
Depending on your latitude, certain stars will be close enough to your nearest pole that they never rise or set. Never dipping below the horizon, they instead circle above you constantly. These are called circumpolar stars.
And the North Star is a special example of a circumpolar star. Because it lies almost exactly above Earth’s northern axis, it’s like the hub of a wheel. It doesn’t rise or set, and barely moves in a circle. Instead, it appears – to the eye – to stay put in the northern sky.
How high in your sky?
The North Star not only points toward the north, but its height in the northern sky also matches your latitude on earth. If you are sailing the Caribbean at 16° north latitude, the North Star will be about 16° high in your sky. If you are sailing around Nova Scotia, at 44° north latitude, then the North Star will be about 44° high in your northern sky. Each degree north or south equals 69 miles (111 km), so traveling 690 miles north or south will change your latitude, and the North Star’s elevation, by 10 degrees.
The 26,000-year precession cycle causes the north celestial pole to move counter-clockwise relative to the background stars. Whichever star is closest to the north celestial pole is called the North Star. Image via Wikimedia Commons.
Taking turns as the North Star
A motion of Earth called precession causes our axis to trace out an imaginary circle on the celestial sphere every 26,000 years. And that means the star closest to the north celestial pole isn’t fixed.
Thousands of years ago, when the pyramids were rising from the sands of ancient Egypt, the North Star was an inconspicuous star called Thuban in the constellation Draco the Dragon.
Twelve thousand years from now, the blue-white star Vega in the constellation Lyra the Harp will be a much brighter North Star than our current Polaris.
Polaris could be a name for any North Star. Our current Polaris used to be called Phoenice. It is the 49th brightest star in the sky. It is not known for its brightness, but for its unique position in the sky.
View at EarthSky Community Photos. | Jeff Grubbs in Elgin, Arizona, captured these star trails on May 22, 2025. Thanks, Jeff! You can see all the stars circling around the star Polaris.
Proper motion
By the way, Polaris – like all stars – has more than one kind of motion. There’s the movement we see on our sky, caused by the Earth’s rotation. And then there’s each star’s actual motion through space.
The stars we see in our night sky are all members of our Milky Way galaxy. All of these stars are moving through space, but they’re so far away we can’t easily see them move. That’s why the stars appear fixed relative to each other. And it’s why, for the most part, we see the same constellations as our ancestors.
But over time, this movement – called proper motion – rearranges the patterns of stars we see in our sky. For Polaris, that movement is small, about 46 arcseconds in 1,000 years. That is about 1/40th of the diameter of the full moon as seen from Earth. So when you’re talking about stars moving or staying fixed, remember … they are all moving through the vastness of space. It’s just the relatively short time of a human lifespan that prevents us from seeing this grand motion.
Bottom line: The North Star is a symbol for constancy. But a video or star trails image reveals that it makes its own little circle around the sky’s north pole every day.
This is RCW 86, the remnant of a Type 1a supernova 8,000 light-years away. Studying Type 1a supernovae led to the discovery that the universe’s expansion is accelerating. An astonishing 2025 study called this discovery into question. But now, new research claims to have found flaws in the 2025 paper. Image via NASA/ CXC/ SAO/ ESA (X-ray)/ JPL-Caltech/ B. Williams (infrared).
No crisis? Universe’s expansion is accelerating after all, study says
Our universe’s expansion is still accelerating despite recent claims suggesting otherwise, an international team of astrophysicists say.
They have refuted a study published last year claiming the growth of the universe is slowing. Instead, the researchers insist there is no flaw in the widely-accepted theory that a mysterious force known as dark energy is driving the expanding cosmos.
The researchers include two Nobel laureates and represent institutions worldwide. They say the debate that followed last November’s revelations was the result of a scientific misunderstanding, rather than a cosmic grenade threatening to blow apart everything we know about the universe.
They published their rebuttal on June 10, 2026, in the peer-reviewed journal Monthly Notices of the Royal Astronomical Society.
Rebutting an extraordinary paper
The new research is a direct rebuttal of a study by a team of South Korean researchers published in November 2025. Their paper made the claim that the universe’s expansion might in fact be slowing down. This would be due to the influence of dark energy – which acts as a kind of anti-gravity – weakening over time.
Lead author Phil Wiseman, from the University of Southampton, said:
The previous and well accepted measurements were, in fact, fine and our current understanding of the fate of the universe remains robust.
Thankfully we have averted this crisis. But the mystery about why the rate of expansion of the universe is still accelerating remains.
By proving our measurements are correct, we can get back to trying to understand what this dark energy actually is, rather than wondering if it exists at all.
What were the flaws?
The international team of researchers involved in the new study included Adam Riess and Brian Schmidt, who collectively won the 2011 Nobel Prize in Physics alongside Saul Perlmutter.
The trio studied Type Ia supernovae, violent, luminous white dwarf star explosions and determined that more distant objects appeared to move faster. This lead to their conclusion that the universe’s expansion was accelerating.
This has been the globally-accepted theory ever since, although last year’s research by the South Korean team threatened to upset the applecart. It claimed that, as the universe aged, these supernovae had different maximum brightnesses. This tricked astronomers into thinking the cosmos was accelerating when it was in fact slowing.
But the University of Southampton-led researchers found an error in how the age of these stars was estimated. They say the previous findings incorrectly assumed the age of a galaxy was the same as the age of the star that exploded.
The experts also said the South Korean paper failed to account for the mass of host galaxies. That is a standard correction used in modern cosmology to prove accuracy.
Riess added:
Extraordinary claims require especially careful testing.
What we find is that when we calibrate these supernovae, accounting for different host environments and populations, the evidence for cosmic acceleration remains remarkably consistent.
Science is never settled
Mark Sullivan, also from the University of Southampton, said challenging accepted theories and observations was fundamental to science.
This is how progress is made. Although this idea did not turn out to be correct, it has opened up new ways of thinking about how supernovae explode and how we can measure dark energy more accurately.
We’ve recently been really focused on astrophysics of the explosions and how they impact cosmology.
This was a good opportunity to go back and go over all of our assumptions; it turns out, yes, we do understand this stuff and we’re accounting for it in our cosmology measurement.
Bottom line: Rebutting a surprising paper from 2025, a new study has found that the universe’s expansion is accelerating after all.
This is RCW 86, the remnant of a Type 1a supernova 8,000 light-years away. Studying Type 1a supernovae led to the discovery that the universe’s expansion is accelerating. An astonishing 2025 study called this discovery into question. But now, new research claims to have found flaws in the 2025 paper. Image via NASA/ CXC/ SAO/ ESA (X-ray)/ JPL-Caltech/ B. Williams (infrared).
No crisis? Universe’s expansion is accelerating after all, study says
Our universe’s expansion is still accelerating despite recent claims suggesting otherwise, an international team of astrophysicists say.
They have refuted a study published last year claiming the growth of the universe is slowing. Instead, the researchers insist there is no flaw in the widely-accepted theory that a mysterious force known as dark energy is driving the expanding cosmos.
The researchers include two Nobel laureates and represent institutions worldwide. They say the debate that followed last November’s revelations was the result of a scientific misunderstanding, rather than a cosmic grenade threatening to blow apart everything we know about the universe.
They published their rebuttal on June 10, 2026, in the peer-reviewed journal Monthly Notices of the Royal Astronomical Society.
Rebutting an extraordinary paper
The new research is a direct rebuttal of a study by a team of South Korean researchers published in November 2025. Their paper made the claim that the universe’s expansion might in fact be slowing down. This would be due to the influence of dark energy – which acts as a kind of anti-gravity – weakening over time.
Lead author Phil Wiseman, from the University of Southampton, said:
The previous and well accepted measurements were, in fact, fine and our current understanding of the fate of the universe remains robust.
Thankfully we have averted this crisis. But the mystery about why the rate of expansion of the universe is still accelerating remains.
By proving our measurements are correct, we can get back to trying to understand what this dark energy actually is, rather than wondering if it exists at all.
What were the flaws?
The international team of researchers involved in the new study included Adam Riess and Brian Schmidt, who collectively won the 2011 Nobel Prize in Physics alongside Saul Perlmutter.
The trio studied Type Ia supernovae, violent, luminous white dwarf star explosions and determined that more distant objects appeared to move faster. This lead to their conclusion that the universe’s expansion was accelerating.
This has been the globally-accepted theory ever since, although last year’s research by the South Korean team threatened to upset the applecart. It claimed that, as the universe aged, these supernovae had different maximum brightnesses. This tricked astronomers into thinking the cosmos was accelerating when it was in fact slowing.
But the University of Southampton-led researchers found an error in how the age of these stars was estimated. They say the previous findings incorrectly assumed the age of a galaxy was the same as the age of the star that exploded.
The experts also said the South Korean paper failed to account for the mass of host galaxies. That is a standard correction used in modern cosmology to prove accuracy.
Riess added:
Extraordinary claims require especially careful testing.
What we find is that when we calibrate these supernovae, accounting for different host environments and populations, the evidence for cosmic acceleration remains remarkably consistent.
Science is never settled
Mark Sullivan, also from the University of Southampton, said challenging accepted theories and observations was fundamental to science.
This is how progress is made. Although this idea did not turn out to be correct, it has opened up new ways of thinking about how supernovae explode and how we can measure dark energy more accurately.
We’ve recently been really focused on astrophysics of the explosions and how they impact cosmology.
This was a good opportunity to go back and go over all of our assumptions; it turns out, yes, we do understand this stuff and we’re accounting for it in our cosmology measurement.
Bottom line: Rebutting a surprising paper from 2025, a new study has found that the universe’s expansion is accelerating after all.
Rastaban and Eltanin, found in the head of Draco the Dragon, represent the Dragon’s Eyes.
Find the Dragon’s Eyes
Tonight, find the Dragon’s Eyes. For years, I’ve glanced up to the north on June evenings and spied the two stars marked on today’s chart, Rastaban and Eltanin in the constellation Draco. They’re noticeable because they’re relatively bright and near each other. There’s always that split second when I ask myself with some excitement what two stars are those? It’s then that my eyes drift to blue-white Vega nearby … and I know, by Vega’s nearness, that they are the stars Rastaban and Eltanin.
These two stars represent the fiery eyes of the constellation Draco the Dragon. Moreover, these stars nearly mark the radiant point for the annual October Draconid meteor shower.
Because the stars stay fixed relative to each other, Vega is always near these stars. Vega, by the way, lodges at the apex of the Summer Triangle, a famous pattern consisting of three bright stars in three separate constellations, also prominent at this time of the year.
Rastaban and Eltanin from around the globe
From tropical and subtropical latitudes in the Southern Hemisphere, the stars Rastaban and Eltanin shine quite low in the northern sky (below Vega). In either hemisphere, at all time zones, the Dragon’s eyes climb highest up in the sky around midnight (1 a.m. daylight saving time) in mid-June, 11 p.m. (midnight daylight saving time) in early July, and 9 p.m. (10 p.m. daylight saving time) in early August. But from temperate latitudes in the Southern Hemisphere (southern Australia and New Zealand), the Dragon’s eyes never climb above your horizon. However, you can catch the star Vega way low in your northern sky.
People at mid-northern latitudes get to view the Dragon’s eyes all night long!
About constellations
Speaking of Rastaban and Eltanin, one of you asked:
What are constellations?
The answer is that they’re patterns of stars on the sky’s dome. The Greeks and Romans, for example, named them for their gods and goddesses, and also for many sorts of animals. In the 20th century, the International Astronomical Union (IAU) formalized the names and boundaries of the constellations. Now every star in the sky belongs to one or another constellation.
The stars within constellations aren’t connected, except in the mind’s eye of stargazers. The stars in general lie at vastly different distances from Earth. It’s by finding juxtaposed patterns on the sky’s dome that you’ll come to know the constellations, much as I identify Rastaban and Eltanin at this time of the year by looking for the star Vega.
The constellation Draco from Urania’s Mirror by Sidney Hall. Image via Wikimedia Commons (public domain).
Bottom line: Look in the northeast on these June evenings, near the star Vega. You’ll see Rastaban and Eltanin, two stars that are bright and close together.
Rastaban and Eltanin, found in the head of Draco the Dragon, represent the Dragon’s Eyes.
Find the Dragon’s Eyes
Tonight, find the Dragon’s Eyes. For years, I’ve glanced up to the north on June evenings and spied the two stars marked on today’s chart, Rastaban and Eltanin in the constellation Draco. They’re noticeable because they’re relatively bright and near each other. There’s always that split second when I ask myself with some excitement what two stars are those? It’s then that my eyes drift to blue-white Vega nearby … and I know, by Vega’s nearness, that they are the stars Rastaban and Eltanin.
These two stars represent the fiery eyes of the constellation Draco the Dragon. Moreover, these stars nearly mark the radiant point for the annual October Draconid meteor shower.
Because the stars stay fixed relative to each other, Vega is always near these stars. Vega, by the way, lodges at the apex of the Summer Triangle, a famous pattern consisting of three bright stars in three separate constellations, also prominent at this time of the year.
Rastaban and Eltanin from around the globe
From tropical and subtropical latitudes in the Southern Hemisphere, the stars Rastaban and Eltanin shine quite low in the northern sky (below Vega). In either hemisphere, at all time zones, the Dragon’s eyes climb highest up in the sky around midnight (1 a.m. daylight saving time) in mid-June, 11 p.m. (midnight daylight saving time) in early July, and 9 p.m. (10 p.m. daylight saving time) in early August. But from temperate latitudes in the Southern Hemisphere (southern Australia and New Zealand), the Dragon’s eyes never climb above your horizon. However, you can catch the star Vega way low in your northern sky.
People at mid-northern latitudes get to view the Dragon’s eyes all night long!
About constellations
Speaking of Rastaban and Eltanin, one of you asked:
What are constellations?
The answer is that they’re patterns of stars on the sky’s dome. The Greeks and Romans, for example, named them for their gods and goddesses, and also for many sorts of animals. In the 20th century, the International Astronomical Union (IAU) formalized the names and boundaries of the constellations. Now every star in the sky belongs to one or another constellation.
The stars within constellations aren’t connected, except in the mind’s eye of stargazers. The stars in general lie at vastly different distances from Earth. It’s by finding juxtaposed patterns on the sky’s dome that you’ll come to know the constellations, much as I identify Rastaban and Eltanin at this time of the year by looking for the star Vega.
The constellation Draco from Urania’s Mirror by Sidney Hall. Image via Wikimedia Commons (public domain).
Bottom line: Look in the northeast on these June evenings, near the star Vega. You’ll see Rastaban and Eltanin, two stars that are bright and close together.
Alan Dyer of Amazingsky.net recorded this video from his home in southern Alberta, Canada, around 51 degrees north latitude. Watch satellites swarm across the night sky in a 2.5-hour time lapse aimed toward the summer Milky Way. Video via Alan Dyer/ AmazingSky.net. Used with permission.
Alan Dyer of Amazingsky.net shared this mind-boggling video of 2.5 hours of the summer Milky Way, as satellites swarmed the view like a plague of locusts. EarthSky reached out to Alan, who captures his images from southern Alberta in Canada. Alan told us:
I take these images to illustrate the satellite issues.
Here are the details he shared about his video:
This 1-minute time-lapse records the tracks of the large number of satellites now passing across our skies on any given night.
The night in question here was June 13-14, 2026, from 11:43 p.m. MDT to 2:10 a.m. MDT [5:43 to 08:10 UTC], so over about 2.5 hours.
I shot this from my location in southern Alberta at 51 degrees north latitude. That latitude range is the worst for seeing satellites in abundance as:
in summer around the solstice even satellites in low-Earth orbit are lit by sunlight all night long, and …
many sets of Starlink satellites peak at the most northerly point in their inclined orbits at about my latitude.
And yes, most of the satellite trails are from SpaceX Starlink satellites as most of the satellites now in orbit are Starlinks. And most seen here are following similar parallel paths, as Starlinks sets do.
Alan shared the photographic details of his video above and the still image below. He wrote:
The fast lens and long exposures I used do make satellites visible that were too faint to see with the unaided eye, just as fainter stars than your eye can see are recorded. Nevertheless, this shows just how many satellites are now passing through any field of view, be it unaided eye, with a camera or with a telescope.
The movie is from 1,200 frames. I took them starting when the sky was still a deep blue in late twilight until past the middle of the short summer night. The final still images stack the first 200 frames taken over 23 minutes, then each subsequent image adds another 100 frames, recording another 12 minutes of trails. This totals 600 frames at the end, taken over 71 minutes … with so many satellite trails the stars are obliterated. And yet this was only half the number of images taken this night.
Alan Dyer shared this composite image looking toward the summer Milky Way from Alberta, Canada. Alan wrote: “This is an accumulation of exposures showing the number of satellites across the Milky Way during 35 minutes, from 12:28 a.m. to 1:03 a.m. on June 14, 2026. The field of view here frames the Summer Triangle. I stacked just 300 frames out of 1,200 I shot this night over 2 hours and 30 minutes. Stacking more frames only produced a dense, chaotic mess, with so many satellite trails the stars were hidden behind a wall of bright streaks.” Image via Alan Dyer/ AmazingSky.net. Used with permission.
Bottom line: Alan Dyer shared this new video as satellites swarm across the sky, obscuring the summer Milky Way. Read more about Alan’s video here.
Alan Dyer of Amazingsky.net recorded this video from his home in southern Alberta, Canada, around 51 degrees north latitude. Watch satellites swarm across the night sky in a 2.5-hour time lapse aimed toward the summer Milky Way. Video via Alan Dyer/ AmazingSky.net. Used with permission.
Alan Dyer of Amazingsky.net shared this mind-boggling video of 2.5 hours of the summer Milky Way, as satellites swarmed the view like a plague of locusts. EarthSky reached out to Alan, who captures his images from southern Alberta in Canada. Alan told us:
I take these images to illustrate the satellite issues.
Here are the details he shared about his video:
This 1-minute time-lapse records the tracks of the large number of satellites now passing across our skies on any given night.
The night in question here was June 13-14, 2026, from 11:43 p.m. MDT to 2:10 a.m. MDT [5:43 to 08:10 UTC], so over about 2.5 hours.
I shot this from my location in southern Alberta at 51 degrees north latitude. That latitude range is the worst for seeing satellites in abundance as:
in summer around the solstice even satellites in low-Earth orbit are lit by sunlight all night long, and …
many sets of Starlink satellites peak at the most northerly point in their inclined orbits at about my latitude.
And yes, most of the satellite trails are from SpaceX Starlink satellites as most of the satellites now in orbit are Starlinks. And most seen here are following similar parallel paths, as Starlinks sets do.
Alan shared the photographic details of his video above and the still image below. He wrote:
The fast lens and long exposures I used do make satellites visible that were too faint to see with the unaided eye, just as fainter stars than your eye can see are recorded. Nevertheless, this shows just how many satellites are now passing through any field of view, be it unaided eye, with a camera or with a telescope.
The movie is from 1,200 frames. I took them starting when the sky was still a deep blue in late twilight until past the middle of the short summer night. The final still images stack the first 200 frames taken over 23 minutes, then each subsequent image adds another 100 frames, recording another 12 minutes of trails. This totals 600 frames at the end, taken over 71 minutes … with so many satellite trails the stars are obliterated. And yet this was only half the number of images taken this night.
Alan Dyer shared this composite image looking toward the summer Milky Way from Alberta, Canada. Alan wrote: “This is an accumulation of exposures showing the number of satellites across the Milky Way during 35 minutes, from 12:28 a.m. to 1:03 a.m. on June 14, 2026. The field of view here frames the Summer Triangle. I stacked just 300 frames out of 1,200 I shot this night over 2 hours and 30 minutes. Stacking more frames only produced a dense, chaotic mess, with so many satellite trails the stars were hidden behind a wall of bright streaks.” Image via Alan Dyer/ AmazingSky.net. Used with permission.
Bottom line: Alan Dyer shared this new video as satellites swarm across the sky, obscuring the summer Milky Way. Read more about Alan’s video here.
There was a nice display of noctilucent clouds last night. Here's the view from the North York Moors, overlooking Teesside at 23:11 UT. #NoctilucentClouds #Noctilucent #NLCs
Noctilucent clouds, or night-shining clouds, are thin clouds high up in Earth’s atmosphere – the mesosphere – as much as 50 miles (80 km) above Earth’s surface. Scientists think they’re made of ice crystals that form on fine dust particles, often from meteors. They can only form when temperatures are incredibly low and when there’s water available to form ice crystals.
So, why do these clouds – which require such cold temperatures – form in the summer? It’s because of the strange dynamics of the atmosphere. At that height in the mesosphere, you actually get the coldest temperatures of the year near the poles in summer. Read on to find out why.
Photo of noctilucent clouds taken in Laboe, Germany, on June 21, 2019. Image by Matthias Süßen/ Wikipedia.
What causes noctilucent clouds?
Here’s how it works: during summer, air close to the ground heats up and rises. Since atmospheric pressure decreases with altitude, the rising air expands. But, when the air expands, it also cools down. This, along with other processes in the upper atmosphere, drives the air even higher causing it to cool even more. As a result, temperatures in the mesosphere can plunge to as low as -225 degrees Fahrenheit (-143 C).
In the Northern Hemisphere, the mesosphere reaches these temperatures by mid-May in most years.
We see noctilucent clouds when most of the sky has grown dark, but the rays from the sun can still reach and reflect off these ethereal, electric-blue clouds. When satellites or astronauts view them from space, they’re referred to as polar mesospheric clouds.
If you want to see them for yourself, now’s the time to look!
Astronauts in the International Space Station (ISS) took this photo on January 5, 2013, when the ISS was over the Pacific Ocean south of French Polynesia. The pale orange band below the brightly lit noctilucent clouds is the stratosphere. Image via NASA.
It’s noctilucent cloud season
The season for noctilucent clouds at northerly latitudes is now. People at high latitudes report seeing noctilucent clouds. This happens every year, from about May through August in the Northern Hemisphere, and from November through February in the Southern Hemisphere.
Sighting them at lower latitudes might be due to a couple of things. According to Royal Museums Greenwich:
In the Northern Hemisphere noctilucent clouds have been seen at much lower latitudes than expected. Scientists believe this is a result of climate change, but it could also be due to other factors, such as rocket launches expelling particles into the atmosphere which go on to form noctilucent clouds.
How to see these night-shining clouds
To see noctilucent clouds, you’ll need certain conditions in your favor. One factor is when to look. Right about now – June to July – is typically when noctilucent clouds are most widespread.
You’ll also want to be positioned as far north as possible during the Northern Hemisphere’s peak season. Canada and the U.K. are two locations where you’ll have a better chance to spot night-shining clouds.
Then, look west about 30 minutes after sunset. The farther north you are, the longer throughout the night you can see them. That’s because the sun doesn’t dip as far below your horizon.
Noctilucent clouds look like electric, luminous tendrils of blue-white light. They are the clouds that glow after other clouds have darkened.
Noctilucent clouds are night-shining clouds because they are so high up that after other clouds are dark, the sun can still reach them. These polar mesospheric clouds appear as eerily blue in a mostly darkened sky. Chart via EarthSky.
What noctilucent clouds can teach us
Noctilucent clouds are sensitive to atmospheric temperatures. Therefore, they can act as a proxy for information about the wind circulation that causes these temperatures. First of all, they can tell scientists that the circulation exists. They can also tell us something about the strength of the circulation.
Scientists studying these clouds got help from NASA’s Aeronomy of Ice in the Mesosphere (AIM) satellite. This satellite, launched in 2007, observed noctilucent clouds using several onboard instruments to collect information such as temperature, atmospheric gases, ice crystal size and changes in the clouds. It even accounted for the amount of meteoric space dust that enters the atmosphere. The AIM spacecraft re-entered Earth’s atmosphere and burned up in August 2024.
View at EarthSky Community Photos. | Petr Horálek braved a cow pasture to get this view of noctilucent clouds on July 3. Petr wrote: “This early morning, the bright NLCs appeared over Central Europe. I found a great spot by Prosec u Sece, Czech Republic. When I started shooting, I found out that cows are close … and a bull too. I was pretty scared of the bull, as he seemed very aggressive, but I managed to make at least one shot before he decided to check me out. So the shot is truly spontaneous and a result of small drama, too.” Thank you, Petr!View at EarthSky Community Photos. | Joel Weatherly captured noctilucent clouds from Edmonton, Alberta, Canada, on July 1. Joel wrote: “Last night we had a significant outbreak of noctilucent clouds. These shimmering NLCs showcased brilliant waves and ripples.” Thank you, Joel!
Noctilucent clouds in 2024
View at EarthSky Community Photos. | Jean-Baptiste Feldmann in Gleizé, France, captured these noctilucent – or night-shining – clouds on July 13. Jean-Baptiste wrote: “Impressive festival of noctilucent clouds a little before 5 in the morning, while I was finishing my planetary observations with the telescope. I had never seen noctilucent with such intensity before. A real treat!” Thank you, Jean-Baptiste!View at EarthSky Community Photos. | Marek Nikodem caught these noctilucent clouds on June 14, from near Szubin, Poland. Thank you, Marek!View at EarthSky Community Photos. | Lorraine Osullivan was in Pembrokeshire, Wales, when she took this image of night-shining clouds on June 25. Lorraine wrote: “I was on holiday when I took this photo, it is taken from our balcony at our cottage.” Thank you, Lorraine!View at EarthSky Community Photos. | Lea Proicheva in Gennep, The Netherlands, captured this image on June 28. Lea wrote: “This time of year the sun goes down very late and twilight last for a long time.” Thank you, Lea!
There was a nice display of noctilucent clouds last night. Here's the view from the North York Moors, overlooking Teesside at 23:11 UT. #NoctilucentClouds #Noctilucent #NLCs
Noctilucent clouds, or night-shining clouds, are thin clouds high up in Earth’s atmosphere – the mesosphere – as much as 50 miles (80 km) above Earth’s surface. Scientists think they’re made of ice crystals that form on fine dust particles, often from meteors. They can only form when temperatures are incredibly low and when there’s water available to form ice crystals.
So, why do these clouds – which require such cold temperatures – form in the summer? It’s because of the strange dynamics of the atmosphere. At that height in the mesosphere, you actually get the coldest temperatures of the year near the poles in summer. Read on to find out why.
Photo of noctilucent clouds taken in Laboe, Germany, on June 21, 2019. Image by Matthias Süßen/ Wikipedia.
What causes noctilucent clouds?
Here’s how it works: during summer, air close to the ground heats up and rises. Since atmospheric pressure decreases with altitude, the rising air expands. But, when the air expands, it also cools down. This, along with other processes in the upper atmosphere, drives the air even higher causing it to cool even more. As a result, temperatures in the mesosphere can plunge to as low as -225 degrees Fahrenheit (-143 C).
In the Northern Hemisphere, the mesosphere reaches these temperatures by mid-May in most years.
We see noctilucent clouds when most of the sky has grown dark, but the rays from the sun can still reach and reflect off these ethereal, electric-blue clouds. When satellites or astronauts view them from space, they’re referred to as polar mesospheric clouds.
If you want to see them for yourself, now’s the time to look!
Astronauts in the International Space Station (ISS) took this photo on January 5, 2013, when the ISS was over the Pacific Ocean south of French Polynesia. The pale orange band below the brightly lit noctilucent clouds is the stratosphere. Image via NASA.
It’s noctilucent cloud season
The season for noctilucent clouds at northerly latitudes is now. People at high latitudes report seeing noctilucent clouds. This happens every year, from about May through August in the Northern Hemisphere, and from November through February in the Southern Hemisphere.
Sighting them at lower latitudes might be due to a couple of things. According to Royal Museums Greenwich:
In the Northern Hemisphere noctilucent clouds have been seen at much lower latitudes than expected. Scientists believe this is a result of climate change, but it could also be due to other factors, such as rocket launches expelling particles into the atmosphere which go on to form noctilucent clouds.
How to see these night-shining clouds
To see noctilucent clouds, you’ll need certain conditions in your favor. One factor is when to look. Right about now – June to July – is typically when noctilucent clouds are most widespread.
You’ll also want to be positioned as far north as possible during the Northern Hemisphere’s peak season. Canada and the U.K. are two locations where you’ll have a better chance to spot night-shining clouds.
Then, look west about 30 minutes after sunset. The farther north you are, the longer throughout the night you can see them. That’s because the sun doesn’t dip as far below your horizon.
Noctilucent clouds look like electric, luminous tendrils of blue-white light. They are the clouds that glow after other clouds have darkened.
Noctilucent clouds are night-shining clouds because they are so high up that after other clouds are dark, the sun can still reach them. These polar mesospheric clouds appear as eerily blue in a mostly darkened sky. Chart via EarthSky.
What noctilucent clouds can teach us
Noctilucent clouds are sensitive to atmospheric temperatures. Therefore, they can act as a proxy for information about the wind circulation that causes these temperatures. First of all, they can tell scientists that the circulation exists. They can also tell us something about the strength of the circulation.
Scientists studying these clouds got help from NASA’s Aeronomy of Ice in the Mesosphere (AIM) satellite. This satellite, launched in 2007, observed noctilucent clouds using several onboard instruments to collect information such as temperature, atmospheric gases, ice crystal size and changes in the clouds. It even accounted for the amount of meteoric space dust that enters the atmosphere. The AIM spacecraft re-entered Earth’s atmosphere and burned up in August 2024.
View at EarthSky Community Photos. | Petr Horálek braved a cow pasture to get this view of noctilucent clouds on July 3. Petr wrote: “This early morning, the bright NLCs appeared over Central Europe. I found a great spot by Prosec u Sece, Czech Republic. When I started shooting, I found out that cows are close … and a bull too. I was pretty scared of the bull, as he seemed very aggressive, but I managed to make at least one shot before he decided to check me out. So the shot is truly spontaneous and a result of small drama, too.” Thank you, Petr!View at EarthSky Community Photos. | Joel Weatherly captured noctilucent clouds from Edmonton, Alberta, Canada, on July 1. Joel wrote: “Last night we had a significant outbreak of noctilucent clouds. These shimmering NLCs showcased brilliant waves and ripples.” Thank you, Joel!
Noctilucent clouds in 2024
View at EarthSky Community Photos. | Jean-Baptiste Feldmann in Gleizé, France, captured these noctilucent – or night-shining – clouds on July 13. Jean-Baptiste wrote: “Impressive festival of noctilucent clouds a little before 5 in the morning, while I was finishing my planetary observations with the telescope. I had never seen noctilucent with such intensity before. A real treat!” Thank you, Jean-Baptiste!View at EarthSky Community Photos. | Marek Nikodem caught these noctilucent clouds on June 14, from near Szubin, Poland. Thank you, Marek!View at EarthSky Community Photos. | Lorraine Osullivan was in Pembrokeshire, Wales, when she took this image of night-shining clouds on June 25. Lorraine wrote: “I was on holiday when I took this photo, it is taken from our balcony at our cottage.” Thank you, Lorraine!View at EarthSky Community Photos. | Lea Proicheva in Gennep, The Netherlands, captured this image on June 28. Lea wrote: “This time of year the sun goes down very late and twilight last for a long time.” Thank you, Lea!
