Additional information about topics covered in this episode of What’s Up, along with still images from the video, and the video transcript, are available at https://science.nasa.gov/skywatching/whats-up/.
Phases of the Moon during March 2025. Credits. NASA JPL
** Two eclipses visible this month! What to see in the night sky, March 2025 – BBC Sky at Night Magazine
Pete Lawrence and Paul Abel reveal the best things to see in the sky throughout March 2025, including a lunar eclipse and solar eclipse.
This month we’ll mark two seasonal transitions, watch eclipses of the Moon and Sun, track down the elusive planet Mercury, and trace out the Winter Hexagon. So grab your curiosity, and come along with Sky & Telescope’s Kelly Beatty on this month’s Sky Tour.
** The Night Sky | March 2025 | Total Lunar Eclipse | Blood Moon | Partial Solar Eclipse – Late Night Astronomy
A total lunar eclipse and partial solar eclipse put on a show for millions of us around the world. Let’s take a look at what you can see in the night sky for March of 2025.
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Timestamps: 0:00 Total Lunar Eclipse 2:21 Partial Solar Eclipse 3:10 The Planets 4:00 Comets
Tylos (or WASP-121b) is a gaseous, giant exoplanet located some 900 light-years away in the constellation Puppis. Using the ESPRESSO instrument on ESO’s Very Large Telescope (VLT), scientists have been able to prove into its atmosphere, revealing its 3D structure. This is the first time that this has been possible on a planet outside of the Solar System. The atmosphere of Tylos is divided into three layers, with iron winds at the bottom, followed by a very fast jet stream of sodium, and finally an upper layer of hydrogen winds. This kind of climate has never been seen before on any planet.
Astronomers have peered through the atmosphere of a planet beyond the Solar System, mapping its 3D structure for the first time. By combining all four telescope units of the European Southern Observatory’s Very Large Telescope (ESO’s VLT), they found powerful winds carrying chemical elements like iron and titanium, creating intricate weather patterns across the planet’s atmosphere. The discovery opens the door for detailed studies of the chemical makeup and weather of other alien worlds.
“This planet’s atmosphere behaves in ways that challenge our understanding of how weather works — not just on Earth, but on all planets. It feels like something out of science fiction,”
says Julia Victoria Seidel, a researcher at the European Southern Observatory (ESO) in Chile and lead author of the study, published today in Nature.
The planet, WASP-121b (also known as Tylos), is some 900 light-years away in the constellation Puppis. It’s an ultra-hot Jupiter, a gas giant orbiting its host star so closely that a year there lasts only about 30 Earth hours. Moreover, one side of the planet is scorching, as it is always facing the star, while the other side is much cooler.
The team has now probed deep inside Tylos’s atmosphere and revealed distinct winds in separate layers, forming a map of the atmosphere’s 3D structure. It’s the first time astronomers have been able to study the atmosphere of a planet outside our Solar System in such depth and detail.
“What we found was surprising: a jet stream rotates material around the planet’s equator, while a separate flow at lower levels of the atmosphere moves gas from the hot side to the cooler side. This kind of climate has never been seen before on any planet,”
says Seidel, who is also a researcher at the Lagrange Laboratory, part of the Observatoire de la Côte d’Azur, in France. The observed jet stream spans half of the planet, gaining speed and violently churning the atmosphere high up in the sky as it crosses the hot side of Tylos.
“Even the strongest hurricanes in the Solar System seem calm in comparison,”
she adds.
This diagram shows the structure and motion of the atmosphere of the exoplanet Tylos (WASP-121b). The exoplanet is shown from above in this figure, looking at one of its poles. The planet rotates counter-clockwise, in such a way that it always shows the same side to its parent star, so it’s always day on one half of the planet and night on the other. The transition between night and day is the “morning side” while the “evening side” represents the transition between day and night; its morning side is to the right and its evening side to the left. As the planet crosses in front of its host star, atoms in the planet’s atmosphere absorb specific colours or wavelengths of the star’s light, which can be measured with a spectrograph. From this data –– obtained in this case with the ESPRESSO instrument on ESO’s Very Large Telescope –– astronomers can reconstruct the composition and velocity of different layers in the atmosphere. The deepest layer is a wind of iron that blows away from the point of the planet where the star is directly overhead. Above this layer there is a very fast jet of sodium that moves faster than the planet rotates. This jet actually accelerates as it moves from the morning side to the evening side of the planet. Finally, there is an upper layer of hydrogen wind blowing outwards. This hydrogen layer overlaps with the sodium jet below it.
To uncover the 3D structure of the exoplanet’s atmosphere, the team used the ESPRESSO instrument on ESO’s VLT to combine the light of its four large telescope units into a single signal. This combined mode of the VLT collects four times as much light as an individual telescope unit, revealing fainter details. By observing the planet for one full transit in front of its host star, ESPRESSO was able to detect signatures of multiple chemical elements, probing different layers of the atmosphere as a result.
“The VLT enabled us to probe three different layers of the exoplanet’s atmosphere in one fell swoop,”
says study co-author Leonardo A. dos Santos, an assistant astronomer at the Space Telescope Science Institute in Baltimore, United States. The team tracked the movements of iron, sodium and hydrogen, which allowed them to trace winds in the deep, mid and shallow layers of the planet’s atmosphere, respectively.
“It’s the kind of observation that is very challenging to do with space telescopes, highlighting the importance of ground-based observations of exoplanets,”
he adds.
Interestingly, the observations also revealed the presence of titanium just below the jet stream, as highlighted in a companion study published in Astronomy and Astrophysics. This was another surprise since previous observations of the planet had shown this element to be absent, possibly because it’s hidden deep in the atmosphere.
“It’s truly mind-blowing that we’re able to study details like the chemical makeup and weather patterns of a planet at such a vast distance,”
says Bibiana Prinoth, a PhD student at Lund University, Sweden, and ESO, who led the companion study and is a co-author of the Nature paper.
To uncover the atmosphere of smaller, Earth-like planets, though, larger telescopes will be needed. They will include ESO’s Extremely Large Telescope (ELT), which is currently under construction in Chile’s Atacama Desert, and its ANDES instrument.
“The ELT will be a game-changer for studying exoplanet atmospheres,” says Prinoth. “This experience makes me feel like we’re on the verge of uncovering incredible things we can only dream about now.”
This image indicates the location of the newly discovered binary star D9, which is orbiting Sagittarius A*, the supermassive black hole at the centre of our galaxy. It is the first star pair ever found near a supermassive black hole. The cut-out shows the binary system as detected by the SINFONI spectrograph on ESO’s Very Large Telescope. While the two stars cannot be discerned separately in this image, the binary nature of D9 was revealed by the spectra captured by SINFONI over several years. These spectra showed that the light emitted by hydrogen gas around D9 oscillates periodically towards red and blue wavelengths as the two stars orbit each other.
An international team of researchers has detected a binary star orbiting close to Sagittarius A*, the supermassive black hole at the centre of our galaxy. It is the first time a stellar pair has been found in the vicinity of a supermassive black hole. The discovery, based on data collected by the European Southern Observatory’s Very Large Telescope (ESO’s VLT), helps us understand how stars survive in environments with extreme gravity, and could pave the way for the detection of planets close to Sagittarius A*.
“Black holes are not as destructive as we thought”
says Florian Peißker, a researcher at the University of Cologne, Germany, and lead author of the study published today in Nature Communications. Binary stars, pairs of stars orbiting each other, are very common in the Universe, but they had never before been found near a supermassive black hole, where the intense gravity can make stellar systems unstable.
This new discovery shows that some binaries can briefly thrive, even under destructive conditions. D9, as the newly discovered binary star is called, was detected just in time: it is estimated to be only 2.7 million years old, and the strong gravitational force of the nearby black hole will probably cause it to merge into a single star within just one million years, a very narrow timespan for such a young system.
“This provides only a brief window on cosmic timescales to observe such a binary system — and we succeeded!”
explains co-author Emma Bordier, a researcher also at the University of Cologne and a former student at ESO.
For many years, scientists also thought that the extreme environment near a supermassive black hole prevented new stars from forming there. Several young stars found in close proximity to Sagittarius A* have disproved this assumption. The discovery of the young binary star now shows that even stellar pairs have the potential to form in these harsh conditions.
“The D9 system shows clear signs of the presence of gas and dust around the stars, which suggests that it could be a very young stellar system that must have formed in the vicinity of the supermassive black hole”
explains co-author Michal Zajaček, a researcher at Masaryk University, Czechia, and the University of Cologne.
The newly discovered binary was found in a dense cluster of stars and other objects orbiting Sagittarius A*, called the S cluster. Most enigmatic in this cluster are the G objects, which behave like stars but look like clouds of gas and dust.
It was during their observations of these mysterious objects that the team found a surprising pattern in D9. The data obtained with the VLT’s ERIS instrument, combined with archival data from the SINFONI instrument, revealed recurring variations in the velocity of the star, indicating D9 was actually two stars orbiting each other.
“I thought that my analysis was wrong,” Peißker says, “but the spectroscopic pattern covered about 15 years, and it was clear this detection is indeed the first binary observed in the S cluster.”
The results shed new light on what the mysterious G objects could be. The team proposes that they might actually be a combination of binary stars that have not yet merged and the leftover material from already merged stars.
The precise nature of many of the objects orbiting Sagittarius A*, as well as how they could have formed so close to the supermassive black hole, remain a mystery. But soon, the GRAVITY+ upgrade to the VLT Interferometer and the METIS instrument on ESO’s Extremely Large Telescope (ELT), under construction in Chile, could change this. Both facilities will allow the team to carry out even more detailed observations of the Galactic centre, revealing the nature of known objects and undoubtedly uncovering more binary stars and young systems.
“Our discovery lets us speculate about the presence of planets, since these are often formed around young stars. It seems plausible that the detection of planets in the Galactic centre is just a matter of time”
concludes Peißker.
This chart shows the location of the field of view within which Sagittarius A* resides — the black hole is marked with a red circle within the constellation of Sagittarius (The Archer). This map shows most of the stars visible to the unaided eye under good conditions.
** What’s Up: December 2024 Skywatching Tips from NASA – NASA JPL
What are some skywatching highlights in December 2024?
This month, enjoy dazzling views of Venus as the “Evening Star,” Jupiter at its brightest during opposition, and Mars doubling in brightness, and look for the Winter Triangle. The Geminid meteor shower peaks under challenging moonlight conditions, but you might get lucky and catch a shooting star that week before sunrise!
0:00 Intro 0:14 December planet highlights 1:31 The Winter Stars 1:57 The Winter Triangle 2:42 Geminid Meteor Shower 3:14 December Moon phases
Additional information about topics covered in this episode of What’s Up, along with still images from the video, and the video transcript, are available at https://solarsystem.nasa.gov/skywatch….
Pete Lawrence and Paul Abel reveal their pick of the best things to see in the night sky this month.
** Sky & Telescope’s Sky Tour Podcast – December 2024 | Jupiter Shines, Winter Stars, and Many Meteors – Sky & Telescope Youtube
Our monthly Sky Tour #astronomy #podcast provides an informative and entertaining 10-minute guided tour of the #night #sky. Join us for the December 2024 episode and mark the #solstice, be amazed by #Jupiter, welcome the arrival of winter’s bright #stars, and prep for what’s usually the year’s best #meteorshower.
Listen and subscribe to this podcast at https://skyandtelescope.org/observing/ and don’t forget to subscribe to S&T’s YouTube channel to get alerts about new videos, including this monthly podcast.
This is an image of the star WOH G64, taken by the GRAVITY instrument on the European Southern Observatory’s Very Large Telescope Interferometer (ESO’s VLTI). This is the first close-up picture of a star outside our own galaxy, the Milky Way. The star is located in the Large Magellanic Cloud, over 160 000 light-years away. The bright oval at the centre of this image is a dusty cocoon that enshrouds the star. A fainter elliptical ring around it could be the inner rim of a dusty torus, but more observations are needed to confirm this feature.
“For the first time, we have succeeded in taking a zoomed-in image of a dying star in a galaxy outside our own Milky Way,”
says Keiichi Ohnaka, an astrophysicist from Universidad Andrés Bello in Chile. Located a staggering 160 000 light-years from us, the star WOH G64 was imaged thanks to the impressive sharpness offered by the European Southern Observatory’s Very Large Telescope Interferometer (ESO’s VLTI). The new observations reveal a star puffing out gas and dust, in the last stages before it becomes a supernova.
“We discovered an egg-shaped cocoon closely surrounding the star,” says Ohnaka, the lead author of a study reporting the observations published today in Astronomy & Astrophysics. “We are excited because this may be related to the drastic ejection of material from the dying star before a supernova explosion.”
While astronomers have taken about two dozen zoomed-in images of stars in our galaxy, unveiling their properties, countless other stars dwell within other galaxies, so far away that observing even one of them in detail has been extremely challenging. Up until now.
The newly imaged star, WOH G64, lies within the Large Magellanic Cloud, one of the small galaxies that orbits the Milky Way. Astronomers have known about this star for decades and have appropriately dubbed it the ‘behemoth star’. With a size roughly 2000 times that of our Sun, WOH G64 is classified as a red supergiant.
Ohnaka’s team had long been interested in this behemoth star. Back in 2005 and 2007, they used ESO’s VLTI in Chile’s Atacama Desert to learn more about the star’s features, and carried on studying it in the years since. But an actual image of the star had remained elusive.
For the desired picture, the team had to wait for the development of one of the VLTI’s second-generation instruments, GRAVITY. After comparing their new results with other previous observations of WOH G64, they were surprised to find that the star had become dimmer over the past decade.
“We have found that the star has been experiencing a significant change in the last 10 years, providing us with a rare opportunity to witness a star’s life in real time,”
says Gerd Weigelt, an astronomy professor at the Max Planck Institute for Radio Astronomy in Bonn, Germany and a co-author of the study. In their final life stages, red supergiants like WOH G64 shed their outer layers of gas and dust in a process that can last thousands of years.
“This star is one of the most extreme of its kind, and any drastic change may bring it closer to an explosive end,”
The team thinks that these shed materials may also be responsible for the dimming and for the unexpected shape of the dust cocoon around the star. The new image shows that the cocoon is stretched-out, which surprised scientists, who expected a different shape based on previous observations and computer models. The team believes that the cocoon’s egg-like shape could be explained by either the star’s shedding or by the influence of a yet-undiscovered companion star.
As the star becomes fainter, taking other close-up pictures of it is becoming increasingly difficult, even for the VLTI. Nonetheless, planned updates to the telescope’s instrumentation, such as the future GRAVITY+, promise to change this soon.
“Similar follow-up observations with ESO instruments will be important for understanding what is going on in the star,”
concludes Ohnaka.
The Large Magellanic Cloud is a satellite galaxy to the Milky Way, located 160 000 light-years away from us. Despite the staggering distance, the GRAVITY instrument of the European Southern Observatory’s Very Large Telescope Interferometer (ESO’s VLTI), managed to take a closed-up picture of the giant star WOH G64. This image shows the location of the star within the Large Magellanic Cloud, with with some of the VLTI’s Auxiliary Telescopes in the foreground.
More information
ESO’s Very Large Telescope Interferometer is able to combine light collected by the telescopes of ESO’s Very Large Telescope (VLT), either the four 8-metre Unit Telescopes or the four smaller Auxiliary Telescopes, creating highly detailed pictures of the cosmos. Effectively, this makes the VLTI a “virtual” telescope with a resolution equivalent to the maximum distance between the individual telescopes. This process is highly complex and needs instruments especially dedicated to this task. Back in 2005 and 2007 Ohnaka’s team had access to the first generation of these instruments: MIDI. While impressive for its time, those observations with MIDI only combined the light from two telescopes. Now, researchers have access to GRAVITY, a second-generation instrument able to capture the light of four telescopes. Its improved sensitivity and resolution made the image of WOH G64 possible. But there is more to come. GRAVITY+ is a planned upgrade of GRAVITY which will be able to take advantage of different technological updates performed at the VLTI and VLT. With these, the VLTI will be able to see objects fainter and farther than ever before.
