Do the giant rings of exoplanet J1407b rotate backward?

View larger. | Artist’s concept of the giant exoplanet J1407b and its immense ring system. A new study suggests the rings may be rotating around the planet backward. Image via Tiouraren/ Wikimedia Commons (CC BY-SA 4.0).

• J1407b is a giant exoplanet with a massive ring system. Scientists think the rings are 200 times larger than Saturn’s.
• The rings may be rotating backward, according to a new study from researchers in China.
• J1407b itself may be a rogue planet, drifting freely in space instead of orbiting a star. But astronomers still don’t know for sure.

The 2025 EarthSky Lunar Calendar is now available! A unique and beautiful poster-sized calendar. Keep up with all phases of the moon every night of the year. Get yours today!

A planet with rings that rotate backward?

J1407b is an enigmatic object that astronomers first detected in 2007. Scientists say it’s likely a huge exoplanet that may have an enormous ring system dwarfing the rings of Saturn. But the exact nature of J1407b isn’t certain even now. Various studies have tried to model the ring system, but there are still many questions. In fact, astronomers are still debating whether J1407b is even orbiting the star J1407 (also known as V1400 Centauri) or if it’s a rogue planet freely drifting in space. On October 29, 2024, yet another new paper entered the discussion. Researchers in China said the planet’s giant rings may be rotating backward.

Kiona Smith wrote about the new study for Inverse on October 30, 2024. Wenshuai Liu, a physicist at Henan Normal University in China, published the preprint version of his paper (not yet peer-reviewed) on arXiv, last revised on October 27, 2024.

The immense ring system of exoplanet J1407b

Astronomers first found J1407b back in 2007, when automated telescopes detected a series of dimming events of the star that lasted for 56 days in April and May. Although the event occurred in 2007, astronomers didn’t find out about it until a few years later. Mark Pecaut, a former graduate student under the supervision of Eric Mamajek at the University of Rochester, discovered the unusual light curve toward the end of 2011.

J1407 is a young star with a mass similar to the sun, lying 451 light-years away. During the eclipse event, the star’s brightness dimmed – varying on a nightly basis – by as much as 95%. Researchers calculated that a massive planet (or brown dwarf?) with a ring system 0.6 AU across was responsible. One AU (astronomical unit) is the average distance from the Earth to the sun. So the rings, if real, were much larger than Saturn’s, about 200 times the diameter. The planet itself was likely tens of times the mass of Jupiter.

Unfortunately, astronomers saw no other eclipses of the star since then. So either the planet has a super-wide orbit – still in the process of completing one orbit since 2007 – or the planet is actually rogue (not bound to any star) and just happened to pass in front of the star at that time from our viewpoint on Earth. Steven Reider then calculated that the planet might be in an elliptical orbit around the star instead of a more circular one.

Read astronomer Matthew Kenworthy’s overview of the J1407b saga, as of 2020

Do the rings of J1407b rotate backward?

This is where the new study comes in. As Smith wrote in Inverse:

Liu simulated how a giant planet and its ring system might form and evolve around a star like V1400 Centauri, which is about the mass of our sun but a few billion years younger. Their models suggest that as giant planets coalesce out of the gas and dust swirling around the star, interactions between those planets can not only nudge some of them into weird, stretched-out orbits, but also set their rings spinning in the wrong direction.

If so, then J1407b’s rings may indeed by rotating backward, that is, in the opposite direction the planet itself rotates. Reider had also posited something similar in 2016.

If the rings orbit around J1407b in the same direction the planet orbits around the star (prograde motion) then the rings should fall apart within only a few orbits. But if the rings rotate in the opposite direction (retrograde motion) then they could hold together for much longer.

View larger. | The rings of J1407b may look more like the swirling disk of dust around the brown dwarf OTS 44, as depicted in this artist’s illustration. Image via NASA/ JPL.

Is J1407b a rogue planet?

Meanwhile, the exact nature of J1407b itself is still debated. It might be a massive planet, or it could be a brown dwarf orbiting the star J1407. But there’s another possibility as well.

It’s possible it’s a rogue planet (or brown dwarf). That would mean it’s drifting all by itself in space, not bound to any star. But if so, then its transit of the star was just a fluke, from our viewpoint on Earth. Astronomers haven’t yet seen it transit the star again, so it’s plausible it was just a one-time event. In addition, another survey in 2019 didn’t find any trace of J1407b at all.

It’s also possible, however, that J1407b is in a very wide orbit around the star. In that case, it would take longer for it to complete one orbit and transit the star again. But that brings up another problem. According to other studies, every time the planet passed closest to the star, in an elliptical orbit, the gravity of the star should strip the rings away.

Backward rotation could protect the rings

There may be a solution, however. Previous studies suggested that if the rings rotated backward, then they could survive the closest approaches to the star. But why, or how, would the rings orbit backward? Liu’s study said the planet may have been “herded” by gravity into a long, narrow orbit after it formed. As Smith wrote:

According to Liu’s simulations, as giant planets coalesce out of the gas and dust swirling around the star, the newly forming planets’ gravity pushed and pulled at one another, jostling the young planets into different orbits, something very similar to the kind of gravitational nudging that sent Jupiter migrating inward during the turbulent early years of our own solar system. Along the way, J1407b got herded into a long, narrow orbit. The complex ways fluids (including flowing clouds of dust in space) interact eventually caused the planet’s little disk of material to start flowing, or orbiting, in the opposite direction from the planet’s rotation and its path around the star.

Is this the answer to the mystery of J1407b? It’s too soon to know yet. First, astronomers need to locate the elusive world again.

Bottom line: The giant exoplanet J1407b is thought to have a massive ring system much larger than Saturn’s. A new study suggests the rings may orbit the planet backward.

Source: Retrograde Ring Formed Around Eccentric Extrasolar Giant Planet

Via Inverse

Via Matthew A. Kenworthy

Read more: Huge distant planet has rings 200 times larger than Saturn’s

Read more: Old photos provide clues about a planet with giant rings

The post Do the giant rings of exoplanet J1407b rotate backward? first appeared on EarthSky.

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View larger. | Artist’s concept of the giant exoplanet J1407b and its immense ring system. A new study suggests the rings may be rotating around the planet backward. Image via Tiouraren/ Wikimedia Commons (CC BY-SA 4.0).

• J1407b is a giant exoplanet with a massive ring system. Scientists think the rings are 200 times larger than Saturn’s.
• The rings may be rotating backward, according to a new study from researchers in China.
• J1407b itself may be a rogue planet, drifting freely in space instead of orbiting a star. But astronomers still don’t know for sure.

The 2025 EarthSky Lunar Calendar is now available! A unique and beautiful poster-sized calendar. Keep up with all phases of the moon every night of the year. Get yours today!

A planet with rings that rotate backward?

J1407b is an enigmatic object that astronomers first detected in 2007. Scientists say it’s likely a huge exoplanet that may have an enormous ring system dwarfing the rings of Saturn. But the exact nature of J1407b isn’t certain even now. Various studies have tried to model the ring system, but there are still many questions. In fact, astronomers are still debating whether J1407b is even orbiting the star J1407 (also known as V1400 Centauri) or if it’s a rogue planet freely drifting in space. On October 29, 2024, yet another new paper entered the discussion. Researchers in China said the planet’s giant rings may be rotating backward.

Kiona Smith wrote about the new study for Inverse on October 30, 2024. Wenshuai Liu, a physicist at Henan Normal University in China, published the preprint version of his paper (not yet peer-reviewed) on arXiv, last revised on October 27, 2024.

The immense ring system of exoplanet J1407b

Astronomers first found J1407b back in 2007, when automated telescopes detected a series of dimming events of the star that lasted for 56 days in April and May. Although the event occurred in 2007, astronomers didn’t find out about it until a few years later. Mark Pecaut, a former graduate student under the supervision of Eric Mamajek at the University of Rochester, discovered the unusual light curve toward the end of 2011.

J1407 is a young star with a mass similar to the sun, lying 451 light-years away. During the eclipse event, the star’s brightness dimmed – varying on a nightly basis – by as much as 95%. Researchers calculated that a massive planet (or brown dwarf?) with a ring system 0.6 AU across was responsible. One AU (astronomical unit) is the average distance from the Earth to the sun. So the rings, if real, were much larger than Saturn’s, about 200 times the diameter. The planet itself was likely tens of times the mass of Jupiter.

Unfortunately, astronomers saw no other eclipses of the star since then. So either the planet has a super-wide orbit – still in the process of completing one orbit since 2007 – or the planet is actually rogue (not bound to any star) and just happened to pass in front of the star at that time from our viewpoint on Earth. Steven Reider then calculated that the planet might be in an elliptical orbit around the star instead of a more circular one.

Read astronomer Matthew Kenworthy’s overview of the J1407b saga, as of 2020

Do the rings of J1407b rotate backward?

This is where the new study comes in. As Smith wrote in Inverse:

Liu simulated how a giant planet and its ring system might form and evolve around a star like V1400 Centauri, which is about the mass of our sun but a few billion years younger. Their models suggest that as giant planets coalesce out of the gas and dust swirling around the star, interactions between those planets can not only nudge some of them into weird, stretched-out orbits, but also set their rings spinning in the wrong direction.

If so, then J1407b’s rings may indeed by rotating backward, that is, in the opposite direction the planet itself rotates. Reider had also posited something similar in 2016.

If the rings orbit around J1407b in the same direction the planet orbits around the star (prograde motion) then the rings should fall apart within only a few orbits. But if the rings rotate in the opposite direction (retrograde motion) then they could hold together for much longer.

View larger. | The rings of J1407b may look more like the swirling disk of dust around the brown dwarf OTS 44, as depicted in this artist’s illustration. Image via NASA/ JPL.

Is J1407b a rogue planet?

Meanwhile, the exact nature of J1407b itself is still debated. It might be a massive planet, or it could be a brown dwarf orbiting the star J1407. But there’s another possibility as well.

It’s possible it’s a rogue planet (or brown dwarf). That would mean it’s drifting all by itself in space, not bound to any star. But if so, then its transit of the star was just a fluke, from our viewpoint on Earth. Astronomers haven’t yet seen it transit the star again, so it’s plausible it was just a one-time event. In addition, another survey in 2019 didn’t find any trace of J1407b at all.

It’s also possible, however, that J1407b is in a very wide orbit around the star. In that case, it would take longer for it to complete one orbit and transit the star again. But that brings up another problem. According to other studies, every time the planet passed closest to the star, in an elliptical orbit, the gravity of the star should strip the rings away.

Backward rotation could protect the rings

There may be a solution, however. Previous studies suggested that if the rings rotated backward, then they could survive the closest approaches to the star. But why, or how, would the rings orbit backward? Liu’s study said the planet may have been “herded” by gravity into a long, narrow orbit after it formed. As Smith wrote:

According to Liu’s simulations, as giant planets coalesce out of the gas and dust swirling around the star, the newly forming planets’ gravity pushed and pulled at one another, jostling the young planets into different orbits, something very similar to the kind of gravitational nudging that sent Jupiter migrating inward during the turbulent early years of our own solar system. Along the way, J1407b got herded into a long, narrow orbit. The complex ways fluids (including flowing clouds of dust in space) interact eventually caused the planet’s little disk of material to start flowing, or orbiting, in the opposite direction from the planet’s rotation and its path around the star.

Is this the answer to the mystery of J1407b? It’s too soon to know yet. First, astronomers need to locate the elusive world again.

Bottom line: The giant exoplanet J1407b is thought to have a massive ring system much larger than Saturn’s. A new study suggests the rings may orbit the planet backward.

Source: Retrograde Ring Formed Around Eccentric Extrasolar Giant Planet

Via Inverse

Via Matthew A. Kenworthy

Read more: Huge distant planet has rings 200 times larger than Saturn’s

Read more: Old photos provide clues about a planet with giant rings

The post Do the giant rings of exoplanet J1407b rotate backward? first appeared on EarthSky.

from EarthSky https://ift.tt/xAhNdnu

Carl Sagan and his scientific legacy on his 90th birthday

It was Carl Sagan who said, “We’re made of starstuff. We are a way for the cosmos to know itself.” Image via NASA/ Wikimedia Commons (public domain).

The 2025 EarthSky Lunar Calendar is here! Get yours today.

• Carl Sagan made major contributions to planetary science. Some of his studies included Venus’ atmosphere and the variations we see on Mars’ surface.
• Sagan was also involved in the search for extraterrestrial intelligence. He was interested in astrobiology, finding what might have brought life to Earth and sending messages to the stars.
• And Sagan was an advocate for Earth. He warned people of climate change and the dangers of nuclear war.

Plus, he inspired generations of future scientists.

By Jean-Luc Margot, University of California, Los Angeles

Carl Sagan and his impact on astronomy

November 9, 2024, would have been Carl Sagan’s 90th birthday. But, sadly, Sagan died in 1996 at the age of 62.

Most people remember him as the co-creator and host of the 1980 Cosmos television series, watched worldwide by hundreds of millions of people. Others read Contact, his best-selling science fiction novel, or The Dragons of Eden, his Pulitzer Prize-winning nonfiction book. Millions more saw him popularize astronomy on The Tonight Show.

What most people don’t know about Sagan, and what has been somewhat obscured by his fame, is the far-reaching impact of his science, which resonates to this day. Sagan was an unequaled science communicator, astute advocate and prolific writer. But he was also an outstanding scientist.

Sagan propelled science forward in at least three important ways. He produced notable results and insights described in over 600 scientific papers. He enabled new scientific disciplines to flourish. And he inspired multiple generations of scientists. As a planetary astronomer, I believe such a combination of talents and accomplishments is rare and may occur only once in my lifetime.

Scientific accomplishments

We knew very little about Venus in the 1960s. Sagan investigated how the greenhouse effect in its carbon dioxide atmosphere might explain the unbearably high temperature on Venus. The planet is approximately 870 degrees Fahrenheit (465 C). His research remains a cautionary tale about the dangers of fossil fuel emissions here on Earth.

Sagan proposed a compelling explanation for seasonal changes in the brightness of Mars. Some scientists incorrectly attributed the changes to vegetation or volcanic activity. But wind-blown dust was responsible for the mysterious variations, he explained.

Sagan and his students studied how changes to the reflectivity of Earth’s surface and atmosphere affect our climate. They considered how the detonation of nuclear bombs could inject so much soot into the atmosphere that it would lead to a yearslong period of substantial cooling. You’ve heard of this phenomenon as nuclear winter.

The study of life in the universe

With unusual breadth in astronomy, physics, chemistry and biology, Sagan pushed forward the nascent discipline of astrobiology, the study of life in the universe. Sagan and research scientist Bishun Khare at Cornell University conducted pioneering laboratory experiments. They showed that certain ingredients of prebiotic chemistry, called tholins, and certain building blocks of life, known as amino acids, form naturally in laboratory environments that mimic planetary settings.

He also modeled the delivery of prebiotic molecules to the early Earth by asteroids and comets. And he was deeply engaged in the biological experiments onboard the Mars Viking landers. Sagan also speculated about the possibility of balloon-shaped organisms floating in the atmospheres of Venus and Jupiter.

Carl Sagan, offering his unique commentary in a scene from Cosmos.

Contributions to SETI

His passion for finding life elsewhere extended far beyond the solar system. He was a champion of the search for extraterrestrial intelligence, also known as SETI. Sagan helped fund and participated in a systematic search for extraterrestrial radio beacons by scanning 70% of the sky with the physicist and electrical engineer Paul Horowitz.

He proposed and co-designed the plaques and the Golden Records now affixed to humanity’s most distant ambassadors, the Pioneer and Voyager spacecrafts. It is unlikely that extraterrestrials will ever find these artifacts, but Sagan wanted people to contemplate the possibility of communication with other civilizations.

Carl Sagan proposed the ‘Golden Record,’ which features the sounds of Earth, including greetings spoken in 55 languages. Image via NASA/ Wikimedia Commons (public domain).

Carl Sagan and his advocacy

Sagan’s scientific output repeatedly led him to become an eloquent advocate on issues of societal and scientific significance. He testified before Congress about the dangers of climate change. He was an antinuclear activist and spoke out against the Strategic Defense Initiative, also known as “Star Wars.” He urged collaborations and a joint space mission with the Soviet Union, in an attempt to improve U.S.-Soviet relations. He spoke directly with members of Congress about the search for extraterrestrial intelligence and organized a petition signed by dozens of prominent scientists urging support for the search.

But perhaps his most important gift to society was his promotion of truth-seeking and critical thinking. He encouraged people to muster the humility and discipline to confront their most cherished beliefs … and to rely on evidence to obtain a more accurate view of the world. His most cited book, The Demon-Haunted World: Science as a Candle in the Dark, is a precious resource for anyone trying to navigate this age of disinformation.

Impact on science and future scientists

A scientist’s impact can sometimes be gauged by the number of times their scholarly work is cited by other scientists. According to Sagan’s Google Scholar page, his work continues to accumulate more than 1,000 citations per year.

Indeed, his current citation rate exceeds that of many members of the National Academy of Sciences, who are “elected by their peers for outstanding contributions to research,” according to the academy’s website. It’s also “one of the highest honors a scientist can receive.”

Sagan was nominated for election into the academy during the 1991-1992 cycle, but his nomination was challenged at the annual meeting. More than 1/3 of the members voted to keep him out, which doomed his admission. An observer at that meeting wrote to Sagan, “It is the worst of human frailties that keeps you out: jealousy.” This belief was affirmed by others in attendance. In my opinion, the academy’s failure to admit Sagan remains an enduring stain on the organization.

No amount of jealousy can diminish Sagan’s profound and wide-ranging legacy. In addition to his scientific accomplishments, Sagan has inspired generations of scientists and brought an appreciation of science to countless nonscientists. He has demonstrated what is possible in the realms of science, communication and advocacy. Those accomplishments required truth-seeking, hard work and self-improvement. On the 90th anniversary of Sagan’s birth, a renewed commitment to these values would honor his memory.

Jean-Luc Margot, Professor of Earth, Planetary, and Space Sciences, University of California, Los Angeles

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Bottom line: Carl Sagan would have turned 90 on November 9, 2024. Here’s a look at his accomplishments and the contributions he made to the world of astronomy and science.

The post Carl Sagan and his scientific legacy on his 90th birthday first appeared on EarthSky.

from EarthSky https://ift.tt/FLof8Kr

It was Carl Sagan who said, “We’re made of starstuff. We are a way for the cosmos to know itself.” Image via NASA/ Wikimedia Commons (public domain).

The 2025 EarthSky Lunar Calendar is here! Get yours today.

• Carl Sagan made major contributions to planetary science. Some of his studies included Venus’ atmosphere and the variations we see on Mars’ surface.
• Sagan was also involved in the search for extraterrestrial intelligence. He was interested in astrobiology, finding what might have brought life to Earth and sending messages to the stars.
• And Sagan was an advocate for Earth. He warned people of climate change and the dangers of nuclear war.

Plus, he inspired generations of future scientists.

By Jean-Luc Margot, University of California, Los Angeles

Carl Sagan and his impact on astronomy

November 9, 2024, would have been Carl Sagan’s 90th birthday. But, sadly, Sagan died in 1996 at the age of 62.

Most people remember him as the co-creator and host of the 1980 Cosmos television series, watched worldwide by hundreds of millions of people. Others read Contact, his best-selling science fiction novel, or The Dragons of Eden, his Pulitzer Prize-winning nonfiction book. Millions more saw him popularize astronomy on The Tonight Show.

What most people don’t know about Sagan, and what has been somewhat obscured by his fame, is the far-reaching impact of his science, which resonates to this day. Sagan was an unequaled science communicator, astute advocate and prolific writer. But he was also an outstanding scientist.

Sagan propelled science forward in at least three important ways. He produced notable results and insights described in over 600 scientific papers. He enabled new scientific disciplines to flourish. And he inspired multiple generations of scientists. As a planetary astronomer, I believe such a combination of talents and accomplishments is rare and may occur only once in my lifetime.

Scientific accomplishments

We knew very little about Venus in the 1960s. Sagan investigated how the greenhouse effect in its carbon dioxide atmosphere might explain the unbearably high temperature on Venus. The planet is approximately 870 degrees Fahrenheit (465 C). His research remains a cautionary tale about the dangers of fossil fuel emissions here on Earth.

Sagan proposed a compelling explanation for seasonal changes in the brightness of Mars. Some scientists incorrectly attributed the changes to vegetation or volcanic activity. But wind-blown dust was responsible for the mysterious variations, he explained.

Sagan and his students studied how changes to the reflectivity of Earth’s surface and atmosphere affect our climate. They considered how the detonation of nuclear bombs could inject so much soot into the atmosphere that it would lead to a yearslong period of substantial cooling. You’ve heard of this phenomenon as nuclear winter.

The study of life in the universe

With unusual breadth in astronomy, physics, chemistry and biology, Sagan pushed forward the nascent discipline of astrobiology, the study of life in the universe. Sagan and research scientist Bishun Khare at Cornell University conducted pioneering laboratory experiments. They showed that certain ingredients of prebiotic chemistry, called tholins, and certain building blocks of life, known as amino acids, form naturally in laboratory environments that mimic planetary settings.

He also modeled the delivery of prebiotic molecules to the early Earth by asteroids and comets. And he was deeply engaged in the biological experiments onboard the Mars Viking landers. Sagan also speculated about the possibility of balloon-shaped organisms floating in the atmospheres of Venus and Jupiter.

Carl Sagan, offering his unique commentary in a scene from Cosmos.

Contributions to SETI

His passion for finding life elsewhere extended far beyond the solar system. He was a champion of the search for extraterrestrial intelligence, also known as SETI. Sagan helped fund and participated in a systematic search for extraterrestrial radio beacons by scanning 70% of the sky with the physicist and electrical engineer Paul Horowitz.

He proposed and co-designed the plaques and the Golden Records now affixed to humanity’s most distant ambassadors, the Pioneer and Voyager spacecrafts. It is unlikely that extraterrestrials will ever find these artifacts, but Sagan wanted people to contemplate the possibility of communication with other civilizations.

Carl Sagan proposed the ‘Golden Record,’ which features the sounds of Earth, including greetings spoken in 55 languages. Image via NASA/ Wikimedia Commons (public domain).

Carl Sagan and his advocacy

Sagan’s scientific output repeatedly led him to become an eloquent advocate on issues of societal and scientific significance. He testified before Congress about the dangers of climate change. He was an antinuclear activist and spoke out against the Strategic Defense Initiative, also known as “Star Wars.” He urged collaborations and a joint space mission with the Soviet Union, in an attempt to improve U.S.-Soviet relations. He spoke directly with members of Congress about the search for extraterrestrial intelligence and organized a petition signed by dozens of prominent scientists urging support for the search.

But perhaps his most important gift to society was his promotion of truth-seeking and critical thinking. He encouraged people to muster the humility and discipline to confront their most cherished beliefs … and to rely on evidence to obtain a more accurate view of the world. His most cited book, The Demon-Haunted World: Science as a Candle in the Dark, is a precious resource for anyone trying to navigate this age of disinformation.

Impact on science and future scientists

A scientist’s impact can sometimes be gauged by the number of times their scholarly work is cited by other scientists. According to Sagan’s Google Scholar page, his work continues to accumulate more than 1,000 citations per year.

Indeed, his current citation rate exceeds that of many members of the National Academy of Sciences, who are “elected by their peers for outstanding contributions to research,” according to the academy’s website. It’s also “one of the highest honors a scientist can receive.”

Sagan was nominated for election into the academy during the 1991-1992 cycle, but his nomination was challenged at the annual meeting. More than 1/3 of the members voted to keep him out, which doomed his admission. An observer at that meeting wrote to Sagan, “It is the worst of human frailties that keeps you out: jealousy.” This belief was affirmed by others in attendance. In my opinion, the academy’s failure to admit Sagan remains an enduring stain on the organization.

No amount of jealousy can diminish Sagan’s profound and wide-ranging legacy. In addition to his scientific accomplishments, Sagan has inspired generations of scientists and brought an appreciation of science to countless nonscientists. He has demonstrated what is possible in the realms of science, communication and advocacy. Those accomplishments required truth-seeking, hard work and self-improvement. On the 90th anniversary of Sagan’s birth, a renewed commitment to these values would honor his memory.

Jean-Luc Margot, Professor of Earth, Planetary, and Space Sciences, University of California, Los Angeles

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Bottom line: Carl Sagan would have turned 90 on November 9, 2024. Here’s a look at his accomplishments and the contributions he made to the world of astronomy and science.

The post Carl Sagan and his scientific legacy on his 90th birthday first appeared on EarthSky.

from EarthSky https://ift.tt/FLof8Kr

Pegasus the Flying Horse, and the best sky story ever

Pegasus the Flying Horse

Pegasus the Flying Horse rises in the east on autumn evenings in the Northern Hemisphere (spring evenings in the Southern Hemisphere). It dominates the sky with its giant square asterism, fittingly called the Great Square. In mythology, Pegasus figured into the greatest – surely the most elaborate – of all sky myths. This one is from ancient Greece some 3,000 years ago. According to the myth, Pegasus was the flying horse ridden by Perseus the Hero, as he swooped in to save Princess Andromeda from a sea monster. There’s more to the story, which you’ll find in the video at the top of this page.

Today, we see Pegasus as the 7th-largest of the 88 official constellations. And Pegasus is easy to find. On fall evenings in the Northern Hemisphere, this constellation climbs above the eastern horizon, reaching a spot nearly overhead by late fall.

Its asterism – the Great Square of Pegasus – is huge. The square alone is 20 degrees wide from top to bottom. That’s the span of two fist-widths held at arm’s length.

On autumn evenings in the Northern Hemisphere – spring evenings in the Southern Hemisphere – Pegasus the Flying Horse is ascending in the east in the evening hours. You’ll most easily notice the giant, square-shaped asterism within Pegasus, called the Great Square.

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Stars of Pegasus

As it rises in the evening, the star in the Great Square closest to the horizon is Algenib, with a magnitude of 2.8. It lies 390 light-years away. The star on the opposite corner of the square from Algenib is Scheat, a magnitude 2.4 star lying 199 light-years away. The star to the south in the square is Markab, a magnitude 2.5 star at a distance of 140 light-years. And the final star in the square is Alpheratz. Technically, Alpheratz lies just across the border of Pegasus and is actually a member of the constellation Andromeda. Alpheratz is the brightest of the four stars at magnitude 2.1 and lies 97 light-years away.

The Great Square marks the body of the flying horse. Trails leading off the west side of the square mark the front legs and head of Pegasus. Extending out from Markab, two stars at magnitude 3.4 and 3.5, Homam and Biham, lead the way to the head star, magnitude 2.4 star Enif. This star is helpful in finding the globular cluster M15.

Find the forelegs of Pegasus off of Scheat. Five degrees west of Scheat is 3rd magnitude star Matar. As the brightest leg star in Pegasus, it’s helpful in finding a couple of notable galaxies.

Pegasus the Flying Horse is a giant constellation that rises in the east on October evenings. Image via Stellarium. Used with permission.

The asterism of the Great Square

The Great Square of Pegasus can look like a huge diamond. Think of it as a giant baseball diamond rising during playoffs month in the east after dark. Asterisms, such as the Great Square, are groups of stars that aren’t labeled as constellations but are easy to recognize.

View at EarthSky Community Photos. | Prateek Pandey in Bhopal, India, captured this photo of Pegasus. He wrote: “Pegasus is named after the winged horse in Greek mythology. Curiously, the constellation Pegasus only represents the top half of the horse. In some depictions, the horse is shown rising out of the water. Viewed best in autumn, turn your eyes to the east as the night falls, and see the winged horse rising high up in the sky.” Thank you, Prateek!

Using Pegasus to find the Andromeda Galaxy

Pegasus is close to the constellation Andromeda, so it’s useful for star-hopping to the Andromeda galaxy. You’ll need a dark-sky site to track down Andromeda without optical aid. It’s much easier to spot with binoculars or a telescope. Follow this link for more information on how to use Pegasus to find Andromeda.

Find the Andromeda Galaxy (M31) by star-hopping from the Great Square of Pegasus. Chart via EarthSky.

View at EarthSky Community Photos. | Jan Curtis in Cheyenne, Wyoming, caught Messier 31, the Andromeda Galaxy, on September 25, 2024. Jan wrote: “M31 is well-placed this time of year for all-night viewing.” Thank you, Jan!

Stephan’s Quintet

Pegasus is home to many galaxy clusters. The most famous is probably Stephan’s Quintet, a favorite target among astrophotographers. This tight gathering of five galaxies has a faint magnitude of 13.6. The largest and brightest, NGC 7320, has a small redshift compared to the other four, revealing that it is probably not a physical member of the group and just a line-of-sight coincidence.

Fun fact: In the 1946 movie It’s a Wonderful Life, angels in heaven discussing George Bailey are depicted as the galaxies in Stephan’s Quintet.

View at EarthSky Community Photos. | Andy Dungan near Cotopaxi, Colorado, captured two galaxy groups, namely Stephan’s Quintet and the Deer Lick Group, both in the constellation Pegasus, on October 27, 2024. Andy wrote: “Over the years I have run into pictures and discussions of these two objects. Both are rather small and close together. Their data and histories are fun too. Both of these would be seen better with a 2,000 mm telescope and my 600 mm telescope with a small format camera takes a pretty good pic. What fun exploring the universe is. I seem to be on a roll lately, lots of clear skies and a motivated photographer.” Thank you, Andy!

This image of Stephan’s Quintet is from 2009, courtesy of the Hubble Space Telescope. Image via Wikimedia Commons (public domain)/ NASA/ ESA/ and the Hubble SM4 ERO Team.

Other galaxies in Pegasus the Flying Horse

Three other notable galaxy clusters lie in Pegasus. The brightest is magnitude 9.5 and is just half a degree from Stephan’s Quintet. The cluster has the curious name Deer Lick Group. Follow Scheat to Matar and then about 4.5 degrees farther and slightly north of the direction you were heading. This will bring you to the Deer Lick Group, NGC 7331. Here you’ll find one large spiral galaxy and a spattering of smaller ones.

The Deer Lick Group contains one large spiral galaxy and other smaller galaxies. It lies in the constellation Pegasus. Image via W4sm astro/ Wikimedia Commons (CC BY-SA 4.0).

The Pegasus I Cluster lies on the southern edge of the constellation not far from the circlet of Pisces. At a distance of 8 degrees from Markab on the sky’s dome, the Pegasus I Cluster is a grouping with a magnitude of 11.1. The galaxy cluster requires a large telescope to see or a long-exposure photograph, but it reveals a beautiful and striking number of galaxies.

The Pegasus II Cluster lies back within the square of Pegasus. Halfway between Alpheratz and Scheat, it lies just inside the border of a line that would be drawn connecting these two stars. A bit dimmer at magnitude 12.6, the Pegasus II Cluster (NGC 7720) is a powerful radio source, the target of much scientific study.

Globular Cluster M15 in Pegasus the Flying Horse

One other deep-sky object of note in Pegasus is the globular cluster M15. You can find M15 easily using the head and neck stars of Pegasus. Start with the star Markab and go to the two dimmer stars that mark the neck. From the last star of the neck (Biham) to the brighter head star Enif, continue a line straight out for a little more than 4 degrees. Here you will find the magnitude 6.4 globular cluster M15. It lies about 33,600 light-years away and will show up nicely in a pair of binoculars.

You can find the globular cluster M15 in the constellation Pegasus. It shines at magnitude 6.4. Image via Mount Lemmon SkyCenter Schulman Telescope/ Adam Block/ Wikimedia Commons (CC BY-SA 4.0).

First exoplanet around a sun-like star

Astronomers discovered the first exoplanet orbiting a sun-like star in the constellation Pegasus. They named the planet 51 Pegasi b after the star it orbits. Didier Queloz and Michel Mayor discovered the planet in 1995 and received the Nobel Prize in Physics for their discovery in 2019.

Artist’s concept of the hot Jupiter exoplanet 51 Pegasi b. The first planet discovered around a sun-like star, 51 Pegasi b lies about 50 light-years from Earth in the constellation Pegasus the Flying Horse. Image via ESO/ M. Kornmesser/ Nick Risinger/ Wikimedia Commons (CC BY 4.0).

Bottom line: Pegasus the Flying Horse is a giant constellation that dominates autumn skies in the Northern Hemisphere (spring skies in the Southern Hemisphere). The constellation contains a famous asterism called the Great Square.

The post Pegasus the Flying Horse, and the best sky story ever first appeared on EarthSky.

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Pegasus the Flying Horse

Pegasus the Flying Horse rises in the east on autumn evenings in the Northern Hemisphere (spring evenings in the Southern Hemisphere). It dominates the sky with its giant square asterism, fittingly called the Great Square. In mythology, Pegasus figured into the greatest – surely the most elaborate – of all sky myths. This one is from ancient Greece some 3,000 years ago. According to the myth, Pegasus was the flying horse ridden by Perseus the Hero, as he swooped in to save Princess Andromeda from a sea monster. There’s more to the story, which you’ll find in the video at the top of this page.

Today, we see Pegasus as the 7th-largest of the 88 official constellations. And Pegasus is easy to find. On fall evenings in the Northern Hemisphere, this constellation climbs above the eastern horizon, reaching a spot nearly overhead by late fall.

Its asterism – the Great Square of Pegasus – is huge. The square alone is 20 degrees wide from top to bottom. That’s the span of two fist-widths held at arm’s length.

On autumn evenings in the Northern Hemisphere – spring evenings in the Southern Hemisphere – Pegasus the Flying Horse is ascending in the east in the evening hours. You’ll most easily notice the giant, square-shaped asterism within Pegasus, called the Great Square.

The 2025 EarthSky Lunar Calendar presale is here! The first 100 purchases are signed by the legendary Deborah Byrd as a thank you. Get yours today!

Stars of Pegasus

As it rises in the evening, the star in the Great Square closest to the horizon is Algenib, with a magnitude of 2.8. It lies 390 light-years away. The star on the opposite corner of the square from Algenib is Scheat, a magnitude 2.4 star lying 199 light-years away. The star to the south in the square is Markab, a magnitude 2.5 star at a distance of 140 light-years. And the final star in the square is Alpheratz. Technically, Alpheratz lies just across the border of Pegasus and is actually a member of the constellation Andromeda. Alpheratz is the brightest of the four stars at magnitude 2.1 and lies 97 light-years away.

The Great Square marks the body of the flying horse. Trails leading off the west side of the square mark the front legs and head of Pegasus. Extending out from Markab, two stars at magnitude 3.4 and 3.5, Homam and Biham, lead the way to the head star, magnitude 2.4 star Enif. This star is helpful in finding the globular cluster M15.

Find the forelegs of Pegasus off of Scheat. Five degrees west of Scheat is 3rd magnitude star Matar. As the brightest leg star in Pegasus, it’s helpful in finding a couple of notable galaxies.

Pegasus the Flying Horse is a giant constellation that rises in the east on October evenings. Image via Stellarium. Used with permission.

The asterism of the Great Square

The Great Square of Pegasus can look like a huge diamond. Think of it as a giant baseball diamond rising during playoffs month in the east after dark. Asterisms, such as the Great Square, are groups of stars that aren’t labeled as constellations but are easy to recognize.

View at EarthSky Community Photos. | Prateek Pandey in Bhopal, India, captured this photo of Pegasus. He wrote: “Pegasus is named after the winged horse in Greek mythology. Curiously, the constellation Pegasus only represents the top half of the horse. In some depictions, the horse is shown rising out of the water. Viewed best in autumn, turn your eyes to the east as the night falls, and see the winged horse rising high up in the sky.” Thank you, Prateek!

Using Pegasus to find the Andromeda Galaxy

Pegasus is close to the constellation Andromeda, so it’s useful for star-hopping to the Andromeda galaxy. You’ll need a dark-sky site to track down Andromeda without optical aid. It’s much easier to spot with binoculars or a telescope. Follow this link for more information on how to use Pegasus to find Andromeda.

Find the Andromeda Galaxy (M31) by star-hopping from the Great Square of Pegasus. Chart via EarthSky.

View at EarthSky Community Photos. | Jan Curtis in Cheyenne, Wyoming, caught Messier 31, the Andromeda Galaxy, on September 25, 2024. Jan wrote: “M31 is well-placed this time of year for all-night viewing.” Thank you, Jan!

Stephan’s Quintet

Pegasus is home to many galaxy clusters. The most famous is probably Stephan’s Quintet, a favorite target among astrophotographers. This tight gathering of five galaxies has a faint magnitude of 13.6. The largest and brightest, NGC 7320, has a small redshift compared to the other four, revealing that it is probably not a physical member of the group and just a line-of-sight coincidence.

Fun fact: In the 1946 movie It’s a Wonderful Life, angels in heaven discussing George Bailey are depicted as the galaxies in Stephan’s Quintet.

View at EarthSky Community Photos. | Andy Dungan near Cotopaxi, Colorado, captured two galaxy groups, namely Stephan’s Quintet and the Deer Lick Group, both in the constellation Pegasus, on October 27, 2024. Andy wrote: “Over the years I have run into pictures and discussions of these two objects. Both are rather small and close together. Their data and histories are fun too. Both of these would be seen better with a 2,000 mm telescope and my 600 mm telescope with a small format camera takes a pretty good pic. What fun exploring the universe is. I seem to be on a roll lately, lots of clear skies and a motivated photographer.” Thank you, Andy!

This image of Stephan’s Quintet is from 2009, courtesy of the Hubble Space Telescope. Image via Wikimedia Commons (public domain)/ NASA/ ESA/ and the Hubble SM4 ERO Team.

Other galaxies in Pegasus the Flying Horse

Three other notable galaxy clusters lie in Pegasus. The brightest is magnitude 9.5 and is just half a degree from Stephan’s Quintet. The cluster has the curious name Deer Lick Group. Follow Scheat to Matar and then about 4.5 degrees farther and slightly north of the direction you were heading. This will bring you to the Deer Lick Group, NGC 7331. Here you’ll find one large spiral galaxy and a spattering of smaller ones.

The Deer Lick Group contains one large spiral galaxy and other smaller galaxies. It lies in the constellation Pegasus. Image via W4sm astro/ Wikimedia Commons (CC BY-SA 4.0).

The Pegasus I Cluster lies on the southern edge of the constellation not far from the circlet of Pisces. At a distance of 8 degrees from Markab on the sky’s dome, the Pegasus I Cluster is a grouping with a magnitude of 11.1. The galaxy cluster requires a large telescope to see or a long-exposure photograph, but it reveals a beautiful and striking number of galaxies.

The Pegasus II Cluster lies back within the square of Pegasus. Halfway between Alpheratz and Scheat, it lies just inside the border of a line that would be drawn connecting these two stars. A bit dimmer at magnitude 12.6, the Pegasus II Cluster (NGC 7720) is a powerful radio source, the target of much scientific study.

Globular Cluster M15 in Pegasus the Flying Horse

One other deep-sky object of note in Pegasus is the globular cluster M15. You can find M15 easily using the head and neck stars of Pegasus. Start with the star Markab and go to the two dimmer stars that mark the neck. From the last star of the neck (Biham) to the brighter head star Enif, continue a line straight out for a little more than 4 degrees. Here you will find the magnitude 6.4 globular cluster M15. It lies about 33,600 light-years away and will show up nicely in a pair of binoculars.

You can find the globular cluster M15 in the constellation Pegasus. It shines at magnitude 6.4. Image via Mount Lemmon SkyCenter Schulman Telescope/ Adam Block/ Wikimedia Commons (CC BY-SA 4.0).

First exoplanet around a sun-like star

Astronomers discovered the first exoplanet orbiting a sun-like star in the constellation Pegasus. They named the planet 51 Pegasi b after the star it orbits. Didier Queloz and Michel Mayor discovered the planet in 1995 and received the Nobel Prize in Physics for their discovery in 2019.

Artist’s concept of the hot Jupiter exoplanet 51 Pegasi b. The first planet discovered around a sun-like star, 51 Pegasi b lies about 50 light-years from Earth in the constellation Pegasus the Flying Horse. Image via ESO/ M. Kornmesser/ Nick Risinger/ Wikimedia Commons (CC BY 4.0).

Bottom line: Pegasus the Flying Horse is a giant constellation that dominates autumn skies in the Northern Hemisphere (spring skies in the Southern Hemisphere). The constellation contains a famous asterism called the Great Square.

The post Pegasus the Flying Horse, and the best sky story ever first appeared on EarthSky.

from EarthSky https://ift.tt/rFLQO0l

Jupiter doesn’t have a surface. How is that possible?

NASA’s Juno spacecraft captured this image of Jupiter in 2020. How is it possible that Jupiter doesn’t have a surface? Image via NASA/ JPL-Caltech/ SwRI/ MSSS/ David Marriott.

• Jupiter is a giant gas planet and the largest planet in our solar system.
• But Jupiter has no surface. It’s made of gases that get increasingly dense as you head toward the center. Its interior is extremely inhospitable.
• If Jupiter didn’t exist, life on Earth probably wouldn’t exist either. That’s because Jupiter protects us from incoming asteroids and comets.

By Benjamin Roulston, Clarkson University

Jupiter doesn’t have a surface. But how?

The planet Jupiter has no solid ground or surface, like the grass or dirt you tread here on Earth. There’s nothing to walk on, and no place to land a spaceship. But how can that be? If Jupiter doesn’t have a surface, what does it have? How can it hold together?

Even as a professor of physics who studies all kinds of unusual phenomena, I realize the concept of a world without a surface is difficult to fathom. Yet much about Jupiter remains a mystery, even as NASA’s robotic probe Juno begins its 9th year orbiting this strange planet.

Jupiter’s mass is 2 1/2 times that of all the other planets in the solar system combined.

The 2025 EarthSky Lunar Calendar presale is here! The first 100 purchases are signed by the legendary Deborah Byrd as a thank you. Get yours today!

First, some facts

Jupiter, the fifth planet from the sun, is between Mars and Saturn. It’s the largest planet in the solar system, big enough for more than 1,000 Earths to fit inside, with room to spare.

While the four inner planets of the solar system – Mercury, Venus, Earth and Mars – are all made of solid, rocky material, Jupiter is a gas giant with a composition similar to the sun. It’s a roiling, stormy, wildly turbulent ball of gas. Some places on Jupiter have winds of more than 400 mph (640 km per hour), about three times faster than a Category 5 hurricane on Earth.

NASA’s Juno spacecraft took this image of the southern hemisphere of Jupiter in 2017. Image via NASA/ JPL-Caltech/ SwRI/ MSSS/ Gerald Eichstadt/ Sean Doran.

Searching for solid ground

Start from the top of Earth’s atmosphere, go down about 60 miles (roughly 100 km), and the air pressure continuously increases. Ultimately you hit Earth’s surface, either land or water.

Compare that with Jupiter: Start near the top of its mostly hydrogen and helium atmosphere, and like on Earth, the pressure increases the deeper you go. But on Jupiter, the pressure is immense.

As the layers of gas above you push down more and more, it’s like being at the bottom of the ocean. But instead of water, you’re surrounded by gas. The pressure becomes so intense that the human body would implode: You would be squashed.

Go down 1,000 miles (1,600 km), and the hot, dense gas begins to behave strangely. Eventually, the gas turns into a form of liquid hydrogen, creating what can be thought of as the largest ocean in the solar system, albeit an ocean without water.

Go down another 20,000 miles (about 32,000 km), and the hydrogen becomes more like flowing liquid metal, a material so exotic that only recently, and with great difficulty, have scientists reproduced it in the laboratory. The atoms in this liquid metallic hydrogen are squeezed so tightly that its electrons are free to roam.

Keep in mind that these layer transitions are gradual, not abrupt. The transition from normal hydrogen gas to liquid hydrogen and then to metallic hydrogen happens slowly and smoothly. At no point is there a sharp boundary, solid material or surface.

An illustration of Jupiter’s interior layers. One bar is approximately equal to the air pressure at sea level on Earth. Image via NASA/ JPL-Caltech.

Scary to the core

Ultimately, you’d reach the core of Jupiter. This is the central region of Jupiter’s interior, and not to be confused with a surface.

Scientists are still debating the exact nature of the core’s material. The most favored model: It’s not solid, like rock, but more like a hot, dense and possibly metallic mixture of liquid and solid.

The pressure at Jupiter’s core is so immense it would be like 100 million Earth atmospheres pressing down on you. Or two Empire State buildings on top of each square inch of your body.

But pressure wouldn’t be your only problem. A spacecraft trying to reach Jupiter’s core would be melted by the extreme heat: 35,000 degrees Fahrenheit (20,000 C). That’s three times hotter than the surface of the sun.

Voyager 1 took this image taken of Jupiter. Note the Great Red Spot, a storm large enough to hold 3 Earths. Image via NASA/ JPL.

Jupiter helps Earth

Jupiter is a weird and forbidding place. But if Jupiter weren’t around, it’s possible human beings might not exist.

That’s because Jupiter acts as a shield for the inner planets of the solar system, including Earth. With its massive gravitational pull, Jupiter has altered the orbit of asteroids and comets for billions of years.

Without Jupiter’s intervention, some of that space debris could have crashed into Earth. If one had been a cataclysmic collision, it could have caused an extinction-level event. Just look at what happened to the dinosaurs.

Maybe Jupiter gave an assist to our existence, but the planet itself is extraordinarily inhospitable to life. At least, life as we know it.

The same is not the case with a Jupiter moon, Europa, perhaps our best chance to find life elsewhere in the solar system.

NASA’s Europa Clipper, a robotic probe that launched in October 2024, will do about 50 flybys over that moon to study its enormous underground ocean.

Could something be living in Europa’s water? Scientists won’t know for a while. Because of Jupiter’s distance from Earth, the probe won’t arrive until April 2030.

Benjamin Roulston, Clarkson University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Bottom line: Jupiter doesn’t have a surface. It’s a gas giant planet with a hostile interior. But if Jupiter didn’t exist, life would probably not exist on Earth.

The post Jupiter doesn’t have a surface. How is that possible? first appeared on EarthSky.

from EarthSky https://ift.tt/l9aIYJS

NASA’s Juno spacecraft captured this image of Jupiter in 2020. How is it possible that Jupiter doesn’t have a surface? Image via NASA/ JPL-Caltech/ SwRI/ MSSS/ David Marriott.

• Jupiter is a giant gas planet and the largest planet in our solar system.
• But Jupiter has no surface. It’s made of gases that get increasingly dense as you head toward the center. Its interior is extremely inhospitable.
• If Jupiter didn’t exist, life on Earth probably wouldn’t exist either. That’s because Jupiter protects us from incoming asteroids and comets.

By Benjamin Roulston, Clarkson University

Jupiter doesn’t have a surface. But how?

The planet Jupiter has no solid ground or surface, like the grass or dirt you tread here on Earth. There’s nothing to walk on, and no place to land a spaceship. But how can that be? If Jupiter doesn’t have a surface, what does it have? How can it hold together?

Even as a professor of physics who studies all kinds of unusual phenomena, I realize the concept of a world without a surface is difficult to fathom. Yet much about Jupiter remains a mystery, even as NASA’s robotic probe Juno begins its 9th year orbiting this strange planet.

Jupiter’s mass is 2 1/2 times that of all the other planets in the solar system combined.

The 2025 EarthSky Lunar Calendar presale is here! The first 100 purchases are signed by the legendary Deborah Byrd as a thank you. Get yours today!

First, some facts

Jupiter, the fifth planet from the sun, is between Mars and Saturn. It’s the largest planet in the solar system, big enough for more than 1,000 Earths to fit inside, with room to spare.

While the four inner planets of the solar system – Mercury, Venus, Earth and Mars – are all made of solid, rocky material, Jupiter is a gas giant with a composition similar to the sun. It’s a roiling, stormy, wildly turbulent ball of gas. Some places on Jupiter have winds of more than 400 mph (640 km per hour), about three times faster than a Category 5 hurricane on Earth.

NASA’s Juno spacecraft took this image of the southern hemisphere of Jupiter in 2017. Image via NASA/ JPL-Caltech/ SwRI/ MSSS/ Gerald Eichstadt/ Sean Doran.

Searching for solid ground

Start from the top of Earth’s atmosphere, go down about 60 miles (roughly 100 km), and the air pressure continuously increases. Ultimately you hit Earth’s surface, either land or water.

Compare that with Jupiter: Start near the top of its mostly hydrogen and helium atmosphere, and like on Earth, the pressure increases the deeper you go. But on Jupiter, the pressure is immense.

As the layers of gas above you push down more and more, it’s like being at the bottom of the ocean. But instead of water, you’re surrounded by gas. The pressure becomes so intense that the human body would implode: You would be squashed.

Go down 1,000 miles (1,600 km), and the hot, dense gas begins to behave strangely. Eventually, the gas turns into a form of liquid hydrogen, creating what can be thought of as the largest ocean in the solar system, albeit an ocean without water.

Go down another 20,000 miles (about 32,000 km), and the hydrogen becomes more like flowing liquid metal, a material so exotic that only recently, and with great difficulty, have scientists reproduced it in the laboratory. The atoms in this liquid metallic hydrogen are squeezed so tightly that its electrons are free to roam.

Keep in mind that these layer transitions are gradual, not abrupt. The transition from normal hydrogen gas to liquid hydrogen and then to metallic hydrogen happens slowly and smoothly. At no point is there a sharp boundary, solid material or surface.

An illustration of Jupiter’s interior layers. One bar is approximately equal to the air pressure at sea level on Earth. Image via NASA/ JPL-Caltech.

Scary to the core

Ultimately, you’d reach the core of Jupiter. This is the central region of Jupiter’s interior, and not to be confused with a surface.

Scientists are still debating the exact nature of the core’s material. The most favored model: It’s not solid, like rock, but more like a hot, dense and possibly metallic mixture of liquid and solid.

The pressure at Jupiter’s core is so immense it would be like 100 million Earth atmospheres pressing down on you. Or two Empire State buildings on top of each square inch of your body.

But pressure wouldn’t be your only problem. A spacecraft trying to reach Jupiter’s core would be melted by the extreme heat: 35,000 degrees Fahrenheit (20,000 C). That’s three times hotter than the surface of the sun.

Voyager 1 took this image taken of Jupiter. Note the Great Red Spot, a storm large enough to hold 3 Earths. Image via NASA/ JPL.

Jupiter helps Earth

Jupiter is a weird and forbidding place. But if Jupiter weren’t around, it’s possible human beings might not exist.

That’s because Jupiter acts as a shield for the inner planets of the solar system, including Earth. With its massive gravitational pull, Jupiter has altered the orbit of asteroids and comets for billions of years.

Without Jupiter’s intervention, some of that space debris could have crashed into Earth. If one had been a cataclysmic collision, it could have caused an extinction-level event. Just look at what happened to the dinosaurs.

Maybe Jupiter gave an assist to our existence, but the planet itself is extraordinarily inhospitable to life. At least, life as we know it.

The same is not the case with a Jupiter moon, Europa, perhaps our best chance to find life elsewhere in the solar system.

NASA’s Europa Clipper, a robotic probe that launched in October 2024, will do about 50 flybys over that moon to study its enormous underground ocean.

Could something be living in Europa’s water? Scientists won’t know for a while. Because of Jupiter’s distance from Earth, the probe won’t arrive until April 2030.

Benjamin Roulston, Clarkson University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Bottom line: Jupiter doesn’t have a surface. It’s a gas giant planet with a hostile interior. But if Jupiter didn’t exist, life would probably not exist on Earth.

The post Jupiter doesn’t have a surface. How is that possible? first appeared on EarthSky.

from EarthSky https://ift.tt/l9aIYJS

Black hole went on a feeding frenzy in the early universe

In this 1-minute video, EarthSky’s Will Triggs tells you about a newly discovered black hole that’s consuming matter 40 times faster than scientists thought was possible.

The 2025 EarthSky Lunar Calendar presale is here! The first 100 purchases are signed by the legendary Deborah Byrd as a thank you. Get yours today!

Supermassive black hole on a feeding frenzy

Supermassive black holes can be some billions of times the mass of our sun. They lie at the center of most galaxies and grow by feeding on nearby stars. But there’s a puzzle. How did supermassive black holes in the early universe get to be so big so fast? On November 4, 2024, astronomers at NOIRLab said they found a distant supermassive black hole consuming material 40 times faster than scientists believed was possible. This feeding frenzy might help explain why supermassive black holes could grow so big early in the age of the universe.

The scientists published their peer-reviewed paper in the journal Nature Astronomy on November 4, 2024.

View larger. | Artist’s concept of a supermassive black hole consuming huge amounts of matter and emitting a powerful outflow of gas. A new study found a supermassive black hole in the early universe experienced a feeding frenzy, consuming material 40 times faster than scientists thought was possible. This discovery could help astronomers understand how supermassive black holes grew so quickly in the early universe. Image via NOIRLab/ NSF/ AURA/ J. da Silva/ M. Zamani.

Meet the hungry black hole

LID-568 is the name of the supermassive black hole that lies at the center of a dwarf galaxy existing just 1.5 billion years after the Big Bang. Lead author Hyewon Suh of NOIRLab and team used the Webb space telescope to peer closely at this supermassive black hole. It showed up intensely in X-rays during a Chandra survey.

Webb’s NIRSpec camera can produce an entire spectrum from each individual pixel. This was crucial in getting data from the early universe. Co-author Emanuele Farina at Gemini International Observatory and NOIRLab said:

Owing to its faint nature, the detection of LID-568 would be impossible without JWST. Using the integral field spectrograph was innovative and necessary for getting our observation.

Thus, these observations allowed the team to discover strong gas outflows at the central black hole. These were likely due to a single episode of rapid accretion. Suh said:

This serendipitous result added a new dimension to our understanding of the system and opened up exciting avenues for investigation.

View larger. | In this artist’s concept we see a dwarf galaxy in the early universe. The inset shows the supermassive black hole at its center that is undergoing a feeding frenzy, gorging on gas and emitting a powerful jet. This supermassive black hole and its dwarf galaxy existed just 1.5 billion years after the Big Bang. Image via NOIRLab/ NSF/ AURA/ J. da Silva/ M. Zamani.

The Eddington limit is not the limit

Previously, astronomers used the Eddington limit to explain the balance between the inward pull of gravity and the outward push of radiation. A black hole can push enough material away that it will cut off its own supply and therefore stop its growth. But LID-568 seems to be consuming matter at 40 times its Eddington limit.

Co-author Julia Scharwächter of NOIRLab said:

This black hole is having a feast. This extreme case shows that a fast-feeding mechanism above the Eddington limit is one of the possible explanations for why we see these very heavy black holes so early in the universe.

So the Eddington limit is not always the limit. LID-568 has shown that black holes can go on feeding frenzies. Suh said:

The discovery of a super-Eddington accreting black hole suggests that a significant portion of mass growth can occur during a single episode of rapid feeding.

So now astronomers will look for more supermassive black holes undergoing feeding frenzies in the early universe. They will appear as nothing more than a few pixels on the best images of the sky available.

Bottom line: A supermassive black hole in the early universe went on a feeding frenzy. It consumied 40 times more material than astronomers thought was possible. This discovery could help answer the puzzle as to why supermassive holes could grow so big so early on in the history of our universe.

Source: A super-Eddington-accreting black hole ~1.5?Gyr after the Big Bang observed with JWST

Via NOIRLab

The post Black hole went on a feeding frenzy in the early universe first appeared on EarthSky.

from EarthSky https://ift.tt/XP3IE9q

In this 1-minute video, EarthSky’s Will Triggs tells you about a newly discovered black hole that’s consuming matter 40 times faster than scientists thought was possible.

The 2025 EarthSky Lunar Calendar presale is here! The first 100 purchases are signed by the legendary Deborah Byrd as a thank you. Get yours today!

Supermassive black hole on a feeding frenzy

Supermassive black holes can be some billions of times the mass of our sun. They lie at the center of most galaxies and grow by feeding on nearby stars. But there’s a puzzle. How did supermassive black holes in the early universe get to be so big so fast? On November 4, 2024, astronomers at NOIRLab said they found a distant supermassive black hole consuming material 40 times faster than scientists believed was possible. This feeding frenzy might help explain why supermassive black holes could grow so big early in the age of the universe.

The scientists published their peer-reviewed paper in the journal Nature Astronomy on November 4, 2024.

View larger. | Artist’s concept of a supermassive black hole consuming huge amounts of matter and emitting a powerful outflow of gas. A new study found a supermassive black hole in the early universe experienced a feeding frenzy, consuming material 40 times faster than scientists thought was possible. This discovery could help astronomers understand how supermassive black holes grew so quickly in the early universe. Image via NOIRLab/ NSF/ AURA/ J. da Silva/ M. Zamani.

Meet the hungry black hole

LID-568 is the name of the supermassive black hole that lies at the center of a dwarf galaxy existing just 1.5 billion years after the Big Bang. Lead author Hyewon Suh of NOIRLab and team used the Webb space telescope to peer closely at this supermassive black hole. It showed up intensely in X-rays during a Chandra survey.

Webb’s NIRSpec camera can produce an entire spectrum from each individual pixel. This was crucial in getting data from the early universe. Co-author Emanuele Farina at Gemini International Observatory and NOIRLab said:

Owing to its faint nature, the detection of LID-568 would be impossible without JWST. Using the integral field spectrograph was innovative and necessary for getting our observation.

Thus, these observations allowed the team to discover strong gas outflows at the central black hole. These were likely due to a single episode of rapid accretion. Suh said:

This serendipitous result added a new dimension to our understanding of the system and opened up exciting avenues for investigation.

View larger. | In this artist’s concept we see a dwarf galaxy in the early universe. The inset shows the supermassive black hole at its center that is undergoing a feeding frenzy, gorging on gas and emitting a powerful jet. This supermassive black hole and its dwarf galaxy existed just 1.5 billion years after the Big Bang. Image via NOIRLab/ NSF/ AURA/ J. da Silva/ M. Zamani.

The Eddington limit is not the limit

Previously, astronomers used the Eddington limit to explain the balance between the inward pull of gravity and the outward push of radiation. A black hole can push enough material away that it will cut off its own supply and therefore stop its growth. But LID-568 seems to be consuming matter at 40 times its Eddington limit.

Co-author Julia Scharwächter of NOIRLab said:

This black hole is having a feast. This extreme case shows that a fast-feeding mechanism above the Eddington limit is one of the possible explanations for why we see these very heavy black holes so early in the universe.

So the Eddington limit is not always the limit. LID-568 has shown that black holes can go on feeding frenzies. Suh said:

The discovery of a super-Eddington accreting black hole suggests that a significant portion of mass growth can occur during a single episode of rapid feeding.

So now astronomers will look for more supermassive black holes undergoing feeding frenzies in the early universe. They will appear as nothing more than a few pixels on the best images of the sky available.

Bottom line: A supermassive black hole in the early universe went on a feeding frenzy. It consumied 40 times more material than astronomers thought was possible. This discovery could help answer the puzzle as to why supermassive holes could grow so big so early on in the history of our universe.

Source: A super-Eddington-accreting black hole ~1.5?Gyr after the Big Bang observed with JWST

Via NOIRLab

The post Black hole went on a feeding frenzy in the early universe first appeared on EarthSky.

from EarthSky https://ift.tt/XP3IE9q

See the Summer Triangle in the northern autumn sky

The Summer Triangle is a famous asterism, consisting of 3 bright stars overhead in northern summer. But you can also easily see it through the northern autumn, and even into winter. Chart via EarthSky.

The 2025 EarthSky Lunar Calendar presale is here! The first 100 purchases are signed by the legendary Deborah Byrd as a thank you. Get yours today!

The Summer Triangle and its 3 stars

The Summer Triangle is the signature star formation in the Northern Hemisphere’s summer sky. However, as the September equinox comes and goes – and as the weeks of autumn begin to slide by – you’ll still notice this famous trio of stars. So, look for the Summer Triangle after dark in early November. It will actually continue to shine after dark in November and December, and is even visible still in January. Look for it tonight in the early evening, high in your western sky.

By the way, the Summer Triangle isn’t a constellation. It’s an asterism, or an obvious pattern or group of stars with a popular name. In fact, the Summer Triangle consists of three bright stars in three separate constellations. The bright star Vega is in Lyra the Harp. Deneb is in Cygnus the Swan. And Altair is in Aquila the Eagle.

In the month of June – around the June solstice – the Summer Triangle pops out in the east as darkness falls and shines all night long. But now – after sunset in November – the Summer Triangle appears high in the western evening sky. As evening deepens, the Summer Triangle descends westward, with all three of its stars staying above the horizon until mid-to-late evening.

Altair – the Summer Triangle’s southernmost star – will set around 10 to 11 p.m. tonight at mid-northern latitudes. Notice where you see the Summer Triangle at a given time this evening. The Summer Triangle will return to this same place in the sky some four minutes earlier with each passing day, or two hours earlier with each passing month.

Look for Orion, too

Then as the Summer Triangle sinks close to the western horizon around mid-evening, turn around to see Orion the Hunter – the signpost constellation of winter – rising in the east.

Bottom line: Look westward this evening for the three brilliant stars of the humongous Summer Triangle: Vega, Deneb and Altair. In fact, you can still see the Summer Triangle through January.

EarthSky astronomy kits are perfect for beginners. Order yours from the EarthSky store.

The post See the Summer Triangle in the northern autumn sky first appeared on EarthSky.

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The Summer Triangle is a famous asterism, consisting of 3 bright stars overhead in northern summer. But you can also easily see it through the northern autumn, and even into winter. Chart via EarthSky.

The 2025 EarthSky Lunar Calendar presale is here! The first 100 purchases are signed by the legendary Deborah Byrd as a thank you. Get yours today!

The Summer Triangle and its 3 stars

The Summer Triangle is the signature star formation in the Northern Hemisphere’s summer sky. However, as the September equinox comes and goes – and as the weeks of autumn begin to slide by – you’ll still notice this famous trio of stars. So, look for the Summer Triangle after dark in early November. It will actually continue to shine after dark in November and December, and is even visible still in January. Look for it tonight in the early evening, high in your western sky.

By the way, the Summer Triangle isn’t a constellation. It’s an asterism, or an obvious pattern or group of stars with a popular name. In fact, the Summer Triangle consists of three bright stars in three separate constellations. The bright star Vega is in Lyra the Harp. Deneb is in Cygnus the Swan. And Altair is in Aquila the Eagle.

In the month of June – around the June solstice – the Summer Triangle pops out in the east as darkness falls and shines all night long. But now – after sunset in November – the Summer Triangle appears high in the western evening sky. As evening deepens, the Summer Triangle descends westward, with all three of its stars staying above the horizon until mid-to-late evening.

Altair – the Summer Triangle’s southernmost star – will set around 10 to 11 p.m. tonight at mid-northern latitudes. Notice where you see the Summer Triangle at a given time this evening. The Summer Triangle will return to this same place in the sky some four minutes earlier with each passing day, or two hours earlier with each passing month.

Look for Orion, too

Then as the Summer Triangle sinks close to the western horizon around mid-evening, turn around to see Orion the Hunter – the signpost constellation of winter – rising in the east.

Bottom line: Look westward this evening for the three brilliant stars of the humongous Summer Triangle: Vega, Deneb and Altair. In fact, you can still see the Summer Triangle through January.

EarthSky astronomy kits are perfect for beginners. Order yours from the EarthSky store.

The post See the Summer Triangle in the northern autumn sky first appeared on EarthSky.

from EarthSky https://ift.tt/UAenhbm

Jupiter’s moons: How to see and enjoy them

The shadow of Io, one of Jupiter’s moons, is cast on the giant planet’s cloud tops. This image was captured by the JunoCam camera aboard NASA’s Juno spacecraft, currently orbiting Jupiter. The image was acquired on September 19, 2019. Image via NASA/ JPL-Caltech/ SwRI/ MSSS/ Kevin M. Gill (public domain).

Jupiter will be brightest in early December, so now is a good time to look for its 4 largest moons. For more events, visit EarthSky’s night sky guide.

Exciting news, EarthSky family! The 2025 Lunar Calendar Presale is live!

How to see Jupiter’s moons

All you need is a good pair of binoculars (or a telescope) to see the four largest moons of the biggest planet in our solar system, Jupiter.

Three of the four moons are bigger than Earth’s moon. And one – Ganymede – is the largest moon in the solar system. These four satellites are collectively called the Galilean moons to honor the Italian astronomer Galileo, who discovered them in 1610. November 2024 is a great month to look for Jupiter’s four large moons. That’s because the king of planets is nearing opposition – when Earth will sweep between it and the sun – in early December. So the distance between Earth and Jupiter is now less than usual. And Jupiter is bright!

From Earth, through a small telescope or strong binoculars, the moons of Jupiter look like tiny starlike pinpricks of light. But you’ll know they’re not stars because you’ll see them stretched out in a line that bisects the giant planet.

Depending on what sort of optical aid you use, you might glimpse just one moon or see all four. If you see fewer than four moons, that might be because a moon is behind – or in front of – Jupiter. If a moon is in front of the planet, you probably can’t see it. The moon is too tiny and gets lost from our view. But observers do sometimes see a moon shadow crossing Jupiter’s cloud-tops. That event is called a transit.

Going from the moon closest to Jupiter to the outermost, their order going outward from Jupiter is Io, Europa, Ganymede and Callisto.

What you’ll see

Writing at SkyandTelescope.com, Bob King has said:

Etched in my brain cells is an image of a sharp, gleaming disk striped with two dark belts and accompanied by four starlike moons through my 2.4-inch [6 cm] refractor in the winter of 1966. A 6-inch [15 cm] reflector will make you privy to nearly all of the planet’s secrets …

When magnified at 150x or higher [Jupiter’s 4 largest moons] lose their starlike appearance and show disks that range in size from 1.0″ to 1.7″ (arcseconds). Europa is the smallest and Ganymede the largest.

Ganymede also casts the largest shadow on the planet’s cloud tops when it transits in front of Jupiter. Shadow transits are visible at least once a week with ‘double transits’ – two moons casting shadows simultaneously – occurring once or twice a month. Ganymede’s shadow looks like a bullet hole, while little Europa’s more resembles a pinprick. Moons also fade away and then reappear over several minutes when they enter and exit Jupiter’s shadow during eclipse. Or a moon may be occulted by the Jovian disk and hover at the planet’s edge like a pearl before fading from sight.

Images of Jupiter’s moons from the EarthSky community

View at EarthSky Community Photos. | Nanci McCraine at Finger Lakes, New York, took this photo on September 30, 2023, and wrote: “I noticed craggy edges around Jupiter. Zooming in, I spotted this line of 4 straight lights across the planet that I assume are satellites.” That is correct! Binoculars or a small telescope will show Jupiter’s moons.

View at EarthSky Community Photos. | Cathy Adams in St. Stephen, New Brunswick, Canada, captured 2 of Jupiter’s moons and giant Jupiter itself on September 3, 2022. Cathy wrote: “After so many cloudy nights I was fortunate to get a beautiful clear one! And it was absolutely wonderful to enjoy a night out observing, and imaging our neighboring planets!!” Thank you, Cathy!

View at EarthSky Community Photos. | Around the time of its yearly opposition, Jupiter is brightest in our sky, best through a telescope, and visible all night. Michael Terhune in Lunenburg, Massachusetts, captured Jupiter in August 2021. He wrote: “My sharpest image of Jupiter! Showing 2 of its Galilean satellites, Io and Europa. The Great Red Spot is also visible.” Thank you, Michael.

More images

View at EarthSky Community Photos. | Meiying Lee in Taipei, Taiwan, took these images of Jupiter’s 4 largest moons over the course of a single night. She wrote: “I always thought that to see obvious changes in the 4 major satellites of Jupiter would take several nights of continuous observation. Later, I discovered that the Galilean satellites move very fast around Jupiter.” See the volcanic moon Io move behind Jupiter and emerge on the other side just a few hours later? Amazing! Thanks, Meiying.

Meiying Lee in Taipei, Taiwan, shared this chart with us on October 6, 2023, and wrote: “From the evening of August 15 to the early morning of August 16, 2021, the Galilean satellites experienced very exciting changes. Callisto, Ganymede, and Europa passed through the surface of Jupiter one after another, while Io was occulted by Jupiter. This resulted in the rare phenomenon that there were no Galilean satellites around Jupiter for 20 minutes late at night on August 16th. Finally, before dawn, the 4 satellites appeared around Jupiter one after another. I watched the Galilean satellites show all night, it was really exciting!” Thank you, Meiying.

View at EarthSky Community Photos. | Sona Shahani Shukla in New Delhi, India, caught a transit of the innermost Galilean moon, Io, across the face of Jupiter on July 7, 2021, and wrote: “Io appears to be skimming Jupiter’s cloud tops, but it’s actually 310,000 miles (500,000 km) from Jupiter. Io zips around Jupiter in 1.8 days, whereas our moon circles Earth every 28 days. The conspicuous black spot on Jupiter is Io’s shadow and is about the size of the moon itself (2,262 miles or 3,640 km across). This shadow sails across the face of Jupiter at 38,000 mph (17 km per second).” Thank you, Sona!

Special viewings of Jupiter’s moons

As with most moons and planets, the Galilean moons orbit Jupiter around its equator. We do see their orbits almost exactly edge-on, but, as with so much in astronomy, there’s a cycle for viewing the edge-on-ness of Jupiter’s moons. This particular cycle is six years long. So every six years we view Jupiter’s equator – and the moons orbiting above its equator – at the most edge-on. During these special times, we can see the moons eclipse and cast shadows on not just giant Jupiter but on each other.

In 2021 we were able to view a number of mutual events (eclipses and shadow transits) involving Jupiter’s moons. The next cycle of mutual events will be in 2027.

Another special event, a rare triple transit, occurs on October 18, 2025, when three of Jupiter’s moons will pass in front of the giant planet at once. The last time Earth could witness a triple transit was in 2021. Triple transits are not visible from all parts of the globe, however.

You can find information here for dates and times to observe the Galilean moons

Composite image of Jupiter and its 4 Galilean moons. From left to right the moons are Io, Europa, Ganymede and Callisto. The Galileo spacecraft obtained the images to make this composite in 1996. Image via NASA Photojournal.

Jupiter at opposition in December 2024

On December 7, 2024, Jupiter is at opposition, when the planet is opposite the sun in the sky as seen from Earth. When Earth passes directly between Jupiter and the sun, we’ll see Jupiter rise at sunset and set at sunrise. Opposition is the middle of the best time of the year to see a planet, since that’s when the planet is up and viewable all night and is generally closest for the year. But any time Jupiter is visible in your sky, you can view Jupiter’s four major moons.

So if you get a chance, grab some binoculars or a small telescope and go see Jupiter’s Galilean moons with your own eyes!

Click here for recommended sky almanacs; they can tell you Jupiter’s rising time in your sky.

Opposition – when Earth is directly between Jupiter and the sun – is the best time to observe the largest planet and its 4 Galilean moons. In 2024, Jupiter’s opposition is December 7. Image via EarthSky.

Bottom line: November and December 2024 are great months for seeing Jupiter’s moons Io, Europa, Ganymede and Callisto with binoculars or a small telescope.

Check here for dates and times to observe the Great Red Spot

The post Jupiter’s moons: How to see and enjoy them first appeared on EarthSky.

from EarthSky https://ift.tt/ZEqRD8v

The shadow of Io, one of Jupiter’s moons, is cast on the giant planet’s cloud tops. This image was captured by the JunoCam camera aboard NASA’s Juno spacecraft, currently orbiting Jupiter. The image was acquired on September 19, 2019. Image via NASA/ JPL-Caltech/ SwRI/ MSSS/ Kevin M. Gill (public domain).

Jupiter will be brightest in early December, so now is a good time to look for its 4 largest moons. For more events, visit EarthSky’s night sky guide.

Exciting news, EarthSky family! The 2025 Lunar Calendar Presale is live!

How to see Jupiter’s moons

All you need is a good pair of binoculars (or a telescope) to see the four largest moons of the biggest planet in our solar system, Jupiter.

Three of the four moons are bigger than Earth’s moon. And one – Ganymede – is the largest moon in the solar system. These four satellites are collectively called the Galilean moons to honor the Italian astronomer Galileo, who discovered them in 1610. November 2024 is a great month to look for Jupiter’s four large moons. That’s because the king of planets is nearing opposition – when Earth will sweep between it and the sun – in early December. So the distance between Earth and Jupiter is now less than usual. And Jupiter is bright!

From Earth, through a small telescope or strong binoculars, the moons of Jupiter look like tiny starlike pinpricks of light. But you’ll know they’re not stars because you’ll see them stretched out in a line that bisects the giant planet.

Depending on what sort of optical aid you use, you might glimpse just one moon or see all four. If you see fewer than four moons, that might be because a moon is behind – or in front of – Jupiter. If a moon is in front of the planet, you probably can’t see it. The moon is too tiny and gets lost from our view. But observers do sometimes see a moon shadow crossing Jupiter’s cloud-tops. That event is called a transit.

Going from the moon closest to Jupiter to the outermost, their order going outward from Jupiter is Io, Europa, Ganymede and Callisto.

What you’ll see

Writing at SkyandTelescope.com, Bob King has said:

Etched in my brain cells is an image of a sharp, gleaming disk striped with two dark belts and accompanied by four starlike moons through my 2.4-inch [6 cm] refractor in the winter of 1966. A 6-inch [15 cm] reflector will make you privy to nearly all of the planet’s secrets …

When magnified at 150x or higher [Jupiter’s 4 largest moons] lose their starlike appearance and show disks that range in size from 1.0″ to 1.7″ (arcseconds). Europa is the smallest and Ganymede the largest.

Ganymede also casts the largest shadow on the planet’s cloud tops when it transits in front of Jupiter. Shadow transits are visible at least once a week with ‘double transits’ – two moons casting shadows simultaneously – occurring once or twice a month. Ganymede’s shadow looks like a bullet hole, while little Europa’s more resembles a pinprick. Moons also fade away and then reappear over several minutes when they enter and exit Jupiter’s shadow during eclipse. Or a moon may be occulted by the Jovian disk and hover at the planet’s edge like a pearl before fading from sight.

Images of Jupiter’s moons from the EarthSky community

View at EarthSky Community Photos. | Nanci McCraine at Finger Lakes, New York, took this photo on September 30, 2023, and wrote: “I noticed craggy edges around Jupiter. Zooming in, I spotted this line of 4 straight lights across the planet that I assume are satellites.” That is correct! Binoculars or a small telescope will show Jupiter’s moons.

View at EarthSky Community Photos. | Cathy Adams in St. Stephen, New Brunswick, Canada, captured 2 of Jupiter’s moons and giant Jupiter itself on September 3, 2022. Cathy wrote: “After so many cloudy nights I was fortunate to get a beautiful clear one! And it was absolutely wonderful to enjoy a night out observing, and imaging our neighboring planets!!” Thank you, Cathy!

View at EarthSky Community Photos. | Around the time of its yearly opposition, Jupiter is brightest in our sky, best through a telescope, and visible all night. Michael Terhune in Lunenburg, Massachusetts, captured Jupiter in August 2021. He wrote: “My sharpest image of Jupiter! Showing 2 of its Galilean satellites, Io and Europa. The Great Red Spot is also visible.” Thank you, Michael.

More images

View at EarthSky Community Photos. | Meiying Lee in Taipei, Taiwan, took these images of Jupiter’s 4 largest moons over the course of a single night. She wrote: “I always thought that to see obvious changes in the 4 major satellites of Jupiter would take several nights of continuous observation. Later, I discovered that the Galilean satellites move very fast around Jupiter.” See the volcanic moon Io move behind Jupiter and emerge on the other side just a few hours later? Amazing! Thanks, Meiying.

Meiying Lee in Taipei, Taiwan, shared this chart with us on October 6, 2023, and wrote: “From the evening of August 15 to the early morning of August 16, 2021, the Galilean satellites experienced very exciting changes. Callisto, Ganymede, and Europa passed through the surface of Jupiter one after another, while Io was occulted by Jupiter. This resulted in the rare phenomenon that there were no Galilean satellites around Jupiter for 20 minutes late at night on August 16th. Finally, before dawn, the 4 satellites appeared around Jupiter one after another. I watched the Galilean satellites show all night, it was really exciting!” Thank you, Meiying.

View at EarthSky Community Photos. | Sona Shahani Shukla in New Delhi, India, caught a transit of the innermost Galilean moon, Io, across the face of Jupiter on July 7, 2021, and wrote: “Io appears to be skimming Jupiter’s cloud tops, but it’s actually 310,000 miles (500,000 km) from Jupiter. Io zips around Jupiter in 1.8 days, whereas our moon circles Earth every 28 days. The conspicuous black spot on Jupiter is Io’s shadow and is about the size of the moon itself (2,262 miles or 3,640 km across). This shadow sails across the face of Jupiter at 38,000 mph (17 km per second).” Thank you, Sona!

Special viewings of Jupiter’s moons

As with most moons and planets, the Galilean moons orbit Jupiter around its equator. We do see their orbits almost exactly edge-on, but, as with so much in astronomy, there’s a cycle for viewing the edge-on-ness of Jupiter’s moons. This particular cycle is six years long. So every six years we view Jupiter’s equator – and the moons orbiting above its equator – at the most edge-on. During these special times, we can see the moons eclipse and cast shadows on not just giant Jupiter but on each other.

In 2021 we were able to view a number of mutual events (eclipses and shadow transits) involving Jupiter’s moons. The next cycle of mutual events will be in 2027.

Another special event, a rare triple transit, occurs on October 18, 2025, when three of Jupiter’s moons will pass in front of the giant planet at once. The last time Earth could witness a triple transit was in 2021. Triple transits are not visible from all parts of the globe, however.

You can find information here for dates and times to observe the Galilean moons

Composite image of Jupiter and its 4 Galilean moons. From left to right the moons are Io, Europa, Ganymede and Callisto. The Galileo spacecraft obtained the images to make this composite in 1996. Image via NASA Photojournal.

Jupiter at opposition in December 2024

On December 7, 2024, Jupiter is at opposition, when the planet is opposite the sun in the sky as seen from Earth. When Earth passes directly between Jupiter and the sun, we’ll see Jupiter rise at sunset and set at sunrise. Opposition is the middle of the best time of the year to see a planet, since that’s when the planet is up and viewable all night and is generally closest for the year. But any time Jupiter is visible in your sky, you can view Jupiter’s four major moons.

So if you get a chance, grab some binoculars or a small telescope and go see Jupiter’s Galilean moons with your own eyes!

Click here for recommended sky almanacs; they can tell you Jupiter’s rising time in your sky.

Opposition – when Earth is directly between Jupiter and the sun – is the best time to observe the largest planet and its 4 Galilean moons. In 2024, Jupiter’s opposition is December 7. Image via EarthSky.

Bottom line: November and December 2024 are great months for seeing Jupiter’s moons Io, Europa, Ganymede and Callisto with binoculars or a small telescope.

Check here for dates and times to observe the Great Red Spot

The post Jupiter’s moons: How to see and enjoy them first appeared on EarthSky.

from EarthSky https://ift.tt/ZEqRD8v