The last leap year was 2024. So 2028 will be our next leap year, a 366-day-long year, with an extra day added to our calendar (February 29). We’ll call that extra day a leap day. It’ll help synchronize our human-created calendars with Earth’s orbit around the sun and with the passing of the seasons. Why do we need the extra day? Blame Earth’s orbit. Our planet takes approximately 365.25 days to orbit the sun once. It’s that .25 that creates the need for a leap year every four years.
During non-leap years, aka common years – like 2026 – the calendar doesn’t take into account the extra quarter of a day required by Earth to complete a single orbit. In essence, the calendar year, which is a human artifact, is faster than the solar year, the 365 days 5 hours 48 minutes 46 seconds that our planet requires to orbit the sun once.
Over time and without correction, the calendar year would drift away from the solar year. And the drift would add up quickly. For example, without correction the calendar year would be off by about one day after four years. It’d be off by about 25 days after 100 years. You can see that, if even more time were to pass without the leap year as a calendar correction, eventually February would be a summer month in the Northern Hemisphere.
Christopher Clavius (1538-1612). This German mathematician and astronomer figured out how and where to place leap years in the Gregorian calendar. Image via Wikipedia.
Leap years and the Gregorian calendar
Leap days were first added to the Julian Calendar in 46 BCE by Julius Caesar at the advice of Sosigenes, an Alexandrian astronomer.
In 1582, Pope Gregory XIII revised the Julian calendar by creating the Gregorian calendar with the assistance of Christopher Clavius, a German mathematician and astronomer. The Gregorian calendar stated that leap days should not be added in years ending in “00” unless that year is also divisible by 400. This additional correction was added to stabilize the calendar over a period of thousands of years and was necessary because solar years are actually slightly less than 365.25 days. In fact, a solar year occurs over a period of 365.2422 days.
When are leap years?
So, according to the rules set forth in the Gregorian calendar, leap years have occurred or will occur during the following years:
Notice that 2000 was a leap year because it is divisible by 400, but that 1900 was not a leap year.
Since 1582, the Gregorian calendar has been gradually adopted as a “civil” international standard for many countries around the world.
Leap year lore
In medieval Ireland and Scotland, women were allowed to propose marriage to men on February 29 of any leap year. A man who rejected the proposal owed a fine to the woman.
Children born on Leap Day have a true birthday every four years. They generally will celebrate their birth on February 28 or March 1.
Some cultures consider a leap year unlucky – for people or animals – all year long.
A view of the sun above the limb of the Earth, from Earth orbit. Image via NASA.
Bottom line: 2026 isn’t a leap year. But 2028 will be. Why do we have leap years?
The last leap year was 2024. So 2028 will be our next leap year, a 366-day-long year, with an extra day added to our calendar (February 29). We’ll call that extra day a leap day. It’ll help synchronize our human-created calendars with Earth’s orbit around the sun and with the passing of the seasons. Why do we need the extra day? Blame Earth’s orbit. Our planet takes approximately 365.25 days to orbit the sun once. It’s that .25 that creates the need for a leap year every four years.
During non-leap years, aka common years – like 2026 – the calendar doesn’t take into account the extra quarter of a day required by Earth to complete a single orbit. In essence, the calendar year, which is a human artifact, is faster than the solar year, the 365 days 5 hours 48 minutes 46 seconds that our planet requires to orbit the sun once.
Over time and without correction, the calendar year would drift away from the solar year. And the drift would add up quickly. For example, without correction the calendar year would be off by about one day after four years. It’d be off by about 25 days after 100 years. You can see that, if even more time were to pass without the leap year as a calendar correction, eventually February would be a summer month in the Northern Hemisphere.
Christopher Clavius (1538-1612). This German mathematician and astronomer figured out how and where to place leap years in the Gregorian calendar. Image via Wikipedia.
Leap years and the Gregorian calendar
Leap days were first added to the Julian Calendar in 46 BCE by Julius Caesar at the advice of Sosigenes, an Alexandrian astronomer.
In 1582, Pope Gregory XIII revised the Julian calendar by creating the Gregorian calendar with the assistance of Christopher Clavius, a German mathematician and astronomer. The Gregorian calendar stated that leap days should not be added in years ending in “00” unless that year is also divisible by 400. This additional correction was added to stabilize the calendar over a period of thousands of years and was necessary because solar years are actually slightly less than 365.25 days. In fact, a solar year occurs over a period of 365.2422 days.
When are leap years?
So, according to the rules set forth in the Gregorian calendar, leap years have occurred or will occur during the following years:
Notice that 2000 was a leap year because it is divisible by 400, but that 1900 was not a leap year.
Since 1582, the Gregorian calendar has been gradually adopted as a “civil” international standard for many countries around the world.
Leap year lore
In medieval Ireland and Scotland, women were allowed to propose marriage to men on February 29 of any leap year. A man who rejected the proposal owed a fine to the woman.
Children born on Leap Day have a true birthday every four years. They generally will celebrate their birth on February 28 or March 1.
Some cultures consider a leap year unlucky – for people or animals – all year long.
A view of the sun above the limb of the Earth, from Earth orbit. Image via NASA.
Bottom line: 2026 isn’t a leap year. But 2028 will be. Why do we have leap years?
View larger. | NASA’s Curiosity rover captured this closeup view of some of the red planet’s boxwork – or “spiderweb” – formations on September 26, 2025. These “spiderwebs” on Mars are evidence for ancient groundwater in Gale Crater. Surprisingly, that groundwater table was higher in elevation and lasted longer than scientists thought. Image via NASA/ JPL-Caltech/ MSSS.
Mars has giant “spiderwebs” on Mount Sharp in Gale Crater. They are a network of geologic ridges and hollows that extend for miles.
NASA’s Curiosity rover has been exploring these ridges – also called boxwork – for the past six months.
Ancient groundwater seeping through large cracks formed the intriguing formations, according to scientists.
NASA’s Curiosity rover has been taking a close look at some spiderwebs on Mars. Not webs made by actual Martian spiders, of course, but sprawling geologic formations that resemble spiderwebs when seen from above. The grid-like formations – called boxwork – consist of ridges about 3 to 6 feet (1 to 2 meters) tall with sandy hollows in between them. They extend for miles in the region of Mount Sharp in Gale Crater. NASA scientists said on February 23, 2026, that ancient groundwater likely formed the intriguing features. Their location on the mountain also suggests that the ancient groundwater table was higher in elevation and longer-lived than previously thought.
The groundwater would have flowed through fractures in the bedrock. In doing so, the water left behind mineral deposits. Later, the areas with the minerals hardened into ridges, while the wind gradually eroded away softer rock, leaving behind the standing ridges. Now we still see the vast network of ridges and hollows, even though the water has long disappeared.
Curiosity has been exploring the spiderweb region for about the past six months.
View larger. | NASA’s Mars Reconnaissance Orbiter captured this image of a network of spiderweb-like ridges – called boxwork by scientists – on Mount Sharp in Gale Crater on Mars on December 10, 2006. Image via NASA/ JPL-Caltech/ University of Arizona.
Maneuvering through the ridges
For the rover, maneuvering through the boxwork ridges can be a bit tricky. The rover can roll across the tops of the ridges, but they are not much wider than the rover itself. Also, Curiosity can move down into the sandy areas between the ridges, but it has to be careful not to get stuck. Operations systems engineer Ashley Stroupe at NASA’s Jet Propulsion Laboratory in Southern California is the Curiosity Rover Planner (Drive) team lead. She said:
It almost feels like a highway we can drive on. But then we have to go down into the hollows, where you need to be mindful of Curiosity’s wheels slipping or having trouble turning in the sand. There’s always a solution. It just takes trying different paths.
Operations systems engineer Ashley Stroupe at NASA’s Jet Propulsion Laboratory is the Curiosity Rover Planner (Drive) team lead. Image via NASA.
How did the boxwork ridges form?
The boxwork ridges are located on the slopes of Mount Sharp, which sits in the middle of Gale Crater and is about 3 miles (5 kilometers) tall. So, how did they form there? Similar formations exist on Earth, in fact, but they are usually only a few centimeters tall at most and found in caves or dry, sandy environments.
The higher elevations of Mount Sharp record a drier period in the history of Gale Crater, which was once a lake billions of years ago. The boxwork formations are surprisingly high up the mountain, however. Mission scientist Tina Seeger at Rice University in Houston, Texas, explained:
Seeing boxwork this far up the mountain suggests the groundwater table had to be pretty high. And that means the water needed for sustaining life could have lasted much longer than we thought looking from orbit.
In addition, orbiting spacecraft have also imaged the boxwork from high above. Intriguingly, the images showed dark lines going across the spiderwebs. Scientists said they were likely central fractures. That’s where the groundwater would have seeped up to the surface. Now, seeing them up close, Curiosity has confirmed they are indeed fractures.
Nodules in the spiderwebs
Additionally, Curiosity has also found other evidence for past groundwater in this region. For example, some of the rocks have bumpy textures comprised of small nodules. But there is another mystery to be solved, too. The nodules aren’t where scientists expected them to be, near the fractures. Instead, they’re along the walls of the ridges and on rocks in the sandy hollows. Seeger said:
We can’t quite explain yet why the nodules appear where they do. Maybe the ridges were cemented by minerals first, and later episodes of groundwater left nodules around them.
While the spiderwebs themselves have nothing to do with Martian life, they do provide new clues about water and habitable conditions in Mars’ past. What other discoveries might be hiding in the webs, waiting to be found?
View larger. | Closeup view of pea-sized nodules in the boxwork (spiderweb) formations. Groundwater formed them billions of years ago. Image via NASA/ JPL-Caltech/ MSSS.
Bottom line: NASA’s Curiosity rover has been investigating “spiderwebs” on Mars. Groundwater formed these grid-like formations of ridges billions of years ago.
View larger. | NASA’s Curiosity rover captured this closeup view of some of the red planet’s boxwork – or “spiderweb” – formations on September 26, 2025. These “spiderwebs” on Mars are evidence for ancient groundwater in Gale Crater. Surprisingly, that groundwater table was higher in elevation and lasted longer than scientists thought. Image via NASA/ JPL-Caltech/ MSSS.
Mars has giant “spiderwebs” on Mount Sharp in Gale Crater. They are a network of geologic ridges and hollows that extend for miles.
NASA’s Curiosity rover has been exploring these ridges – also called boxwork – for the past six months.
Ancient groundwater seeping through large cracks formed the intriguing formations, according to scientists.
NASA’s Curiosity rover has been taking a close look at some spiderwebs on Mars. Not webs made by actual Martian spiders, of course, but sprawling geologic formations that resemble spiderwebs when seen from above. The grid-like formations – called boxwork – consist of ridges about 3 to 6 feet (1 to 2 meters) tall with sandy hollows in between them. They extend for miles in the region of Mount Sharp in Gale Crater. NASA scientists said on February 23, 2026, that ancient groundwater likely formed the intriguing features. Their location on the mountain also suggests that the ancient groundwater table was higher in elevation and longer-lived than previously thought.
The groundwater would have flowed through fractures in the bedrock. In doing so, the water left behind mineral deposits. Later, the areas with the minerals hardened into ridges, while the wind gradually eroded away softer rock, leaving behind the standing ridges. Now we still see the vast network of ridges and hollows, even though the water has long disappeared.
Curiosity has been exploring the spiderweb region for about the past six months.
View larger. | NASA’s Mars Reconnaissance Orbiter captured this image of a network of spiderweb-like ridges – called boxwork by scientists – on Mount Sharp in Gale Crater on Mars on December 10, 2006. Image via NASA/ JPL-Caltech/ University of Arizona.
Maneuvering through the ridges
For the rover, maneuvering through the boxwork ridges can be a bit tricky. The rover can roll across the tops of the ridges, but they are not much wider than the rover itself. Also, Curiosity can move down into the sandy areas between the ridges, but it has to be careful not to get stuck. Operations systems engineer Ashley Stroupe at NASA’s Jet Propulsion Laboratory in Southern California is the Curiosity Rover Planner (Drive) team lead. She said:
It almost feels like a highway we can drive on. But then we have to go down into the hollows, where you need to be mindful of Curiosity’s wheels slipping or having trouble turning in the sand. There’s always a solution. It just takes trying different paths.
Operations systems engineer Ashley Stroupe at NASA’s Jet Propulsion Laboratory is the Curiosity Rover Planner (Drive) team lead. Image via NASA.
How did the boxwork ridges form?
The boxwork ridges are located on the slopes of Mount Sharp, which sits in the middle of Gale Crater and is about 3 miles (5 kilometers) tall. So, how did they form there? Similar formations exist on Earth, in fact, but they are usually only a few centimeters tall at most and found in caves or dry, sandy environments.
The higher elevations of Mount Sharp record a drier period in the history of Gale Crater, which was once a lake billions of years ago. The boxwork formations are surprisingly high up the mountain, however. Mission scientist Tina Seeger at Rice University in Houston, Texas, explained:
Seeing boxwork this far up the mountain suggests the groundwater table had to be pretty high. And that means the water needed for sustaining life could have lasted much longer than we thought looking from orbit.
In addition, orbiting spacecraft have also imaged the boxwork from high above. Intriguingly, the images showed dark lines going across the spiderwebs. Scientists said they were likely central fractures. That’s where the groundwater would have seeped up to the surface. Now, seeing them up close, Curiosity has confirmed they are indeed fractures.
Nodules in the spiderwebs
Additionally, Curiosity has also found other evidence for past groundwater in this region. For example, some of the rocks have bumpy textures comprised of small nodules. But there is another mystery to be solved, too. The nodules aren’t where scientists expected them to be, near the fractures. Instead, they’re along the walls of the ridges and on rocks in the sandy hollows. Seeger said:
We can’t quite explain yet why the nodules appear where they do. Maybe the ridges were cemented by minerals first, and later episodes of groundwater left nodules around them.
While the spiderwebs themselves have nothing to do with Martian life, they do provide new clues about water and habitable conditions in Mars’ past. What other discoveries might be hiding in the webs, waiting to be found?
View larger. | Closeup view of pea-sized nodules in the boxwork (spiderweb) formations. Groundwater formed them billions of years ago. Image via NASA/ JPL-Caltech/ MSSS.
Bottom line: NASA’s Curiosity rover has been investigating “spiderwebs” on Mars. Groundwater formed these grid-like formations of ridges billions of years ago.
Artist’s depiction of a fearsome-looking Spinosaurus mirabilis standing at the river’s edge. This newly discovered species, one of the last spinosaurid species before they went extinct, lived 95 million years ago in present-day Niger, Africa. Image via Dani Navarro/ University of Chicago. Used with permission.
Scientists discovered a new dinosaur species, Spinosaurus mirabilis, in the Sahara Desert of Niger.
The new species had a tall, scimitar-shaped head crest and lived about 95 million years ago, hunting fish in rivers.
This discovery suggests spinosaurs might have lived inland in forested river habitats, not just near the coast.
Newly discovered dinosaur had an eye-catching head crest
Spinosaurs were large dinosaurs that lived about 100 to 94 million years ago. They were notable for distinctive projections on their backs that looked like sails. Scientists first discovered this dinosaur genus in 1915, and for a long time, there was just one recognized species. But on February 19, 2026, a research team led by Paul Sereno, a paleontologist at the University of Chicago, said they’ve discovered a new spinosaur species in the Central Sahara Desert. They named it Spinosaurus mirabilis – mirabilis means “astonishing” in Latin – because it had an unusual, tall crest on its head.
This find was so sudden and amazing, it was really emotional for our team. I’ll forever cherish the moment in camp when we crowded around a laptop to look at the new species for the first time, after one member of our team generated 3D digital models of the bones we found to assemble the skull, on solar power in the middle of the Sahara. That’s when the significance of the discovery really registered.
Sereno and his colleagues published their findings in the peer-reviewed journal Nature on February 19, 2026.
University of Chicago paleontologist Paul Sereno led the team that excavated and identified the new spinosaur, Spinosaurus mirabilis. He poses here with the skull cast. Image via Keith Ladzinski/ University of Chicago. Used with permission.
This Spinosaurus was a dramatic-looking creature!
Spinosaurs lived 100 to 94 million years ago in present-day Africa. Until now, researchers only recognized one species, Spinosaurus aegyptiacus. Scientists found those fossils at sites that were once coastal habitats when the animals were alive. Therefore, they thought these dinosaurs could be aquatic or semi-aquatic, capable of hunting for fish in the sea. But the degree to which they took to the water was not clear.
These dinosaurs had upward-projecting bones from their backs, creating stunning sail-like features. The animals likely used the sail for display, and it may have even regulated body temperature. In addition, S. aegyptiacus had a long skull similar to crocodiles, optimized for catching fish.
These unusual dinosaurs became extinct about 94 million years ago, due to a rapid rise in sea level and climate change.
A video of Paul Sereno and his team in the field, in Niger, in 2022. Provided by the University of Chicago.
Finding a new Spinosaurus in Niger
In 2019, a local man in the Republic of Niger led Sereno and his team to a site called Jenguebi that had large fossil bones. Due to the long journey back to camp, the team only had time to grab a few fossils, including teeth and jawbones. But they did not yet know it was a new dinosaur species.
In 2022, Sereno returned to Jenguebi with a larger team. During that expedition, they found more fossils there, as well as many more at a site called Iguidi. In all, they were able to collect incomplete skeletons from several individuals, all of them immature spinosaurs that had not reached adulthood.
He said:
The local people we work with are my lifelong friends, now including the man who led us to Jenguebi and the astonishing spinosaur. They understand the importance of what we’re doing together, for science and for their country.
Dan Vidal, a member of Sereno’s team, with Abdoul Nasser, a guide who led them to the Jenguebi fossil site in 2019. There, they found the first Spinosaurus mirabilis fossils. Image via Alhadji Akamaya/ University of Chicago. Used with permission.
Spinosaurus mirabilis
During the 2022 expedition, as they examined their finds, the team realized they had discovered a species new to science. This spinosaur had an unusually tall head crest. Also, the teeth arrangement in its jaw was a bit different from that of S. aegyptiacus.
The new spinosaur had a crest at the top of the skull that the researchers described as scimitar-shaped. That’s a short sword with a curved blade that becomes broader at its tip. In addition, internal vascular canals and the surface texture of the crest suggested it was once coated in keratin. That’s a fibrous protein found in hair, nails and horns. Moreover, they speculated this crest might have been brightly colored.
Ana Lázaro, a member of Sereno’s 2022 expedition to Niger, holds the most complete head crest found for Spinosaurus mirabilis. Image via Alvaro Simarro/ University of Chicago. Used with permission.
S. mirabilis’ jaws were quite formidable, similar to those of S. aegyptiacus. It had interdigitating upper and lower tooth rows. In other words, the teeth in the lower jaw extended outward. Meanwhile, the lower jaw teeth interlocked with those in the upper jaw. This is a feature that exists in many fish-eating animals in the fossil record, such as ichthyosaurs, pterosaurs and some crocodiles.
These are 2 skull casts of spinosaurs. At the top is the newly discovered Spinosaurus mirabilis, and below it is the previously known Spinosaurus aegyptiacus from North Africa. Image via Keith Ladzinski/ University of Chicago. Used with permission.
The bones they collected all came from subadult animals. Therefore, it’s hard to determine the size of an adult S. mirabilis. However, they were able to establish that the individual initially used to describe the species – the holotype – was about 26 feet (8 meters) long.
New clues to how spinosaurs lived
The previously known S. aegyptiacus was found in North Africa, at locations that were once coastal habitat when the animals were alive. Scientists wondered if spinosaurs were fully aquatic and able to dive for prey. But there was considerable debate about it.
However, this new discovery paints a different picture of how spinosaurs may have lived. About 95 million years ago, Jenguebi was 310 miles (500 km) from the coastline. Iguidi was even further away, about 620 miles (1,000 km). That’s pretty far inland from the ocean.
Moreover, the scientists also found fossils from two long-necked dinosaurs (sauropods) near the S. mirabilis fossils. In fact, all those bones had been buried in river sediment. This indicated that S. mirabilis and the other dinosaurs lived in close proximity, in an inland forested habitat that had a network of rivers. Therefore, the researchers think S. mirabilis hunted for fish in shallow water.
Sereno commented:
I envision this dinosaur as a kind of ‘hell heron’ that had no problem wading on its sturdy legs into two meters of water but probably spent most of its time stalking shallower traps for the many large fish of the day.
Artist’s illustration of a pair of Spinosaurus mirabilis fighting over the carcass of an ancient fish on the bank of a river in an inland forest, about 95 million years ago. Image via Dani Navarro/ University of Chicago. Used with permission.
Bottom line: Scientists discovered a previously unknown 95-million-year-old spinosaur species, Spinosaurus mirabilis, in Niger, Africa, which had a tall crest on its head.
Artist’s depiction of a fearsome-looking Spinosaurus mirabilis standing at the river’s edge. This newly discovered species, one of the last spinosaurid species before they went extinct, lived 95 million years ago in present-day Niger, Africa. Image via Dani Navarro/ University of Chicago. Used with permission.
Scientists discovered a new dinosaur species, Spinosaurus mirabilis, in the Sahara Desert of Niger.
The new species had a tall, scimitar-shaped head crest and lived about 95 million years ago, hunting fish in rivers.
This discovery suggests spinosaurs might have lived inland in forested river habitats, not just near the coast.
Newly discovered dinosaur had an eye-catching head crest
Spinosaurs were large dinosaurs that lived about 100 to 94 million years ago. They were notable for distinctive projections on their backs that looked like sails. Scientists first discovered this dinosaur genus in 1915, and for a long time, there was just one recognized species. But on February 19, 2026, a research team led by Paul Sereno, a paleontologist at the University of Chicago, said they’ve discovered a new spinosaur species in the Central Sahara Desert. They named it Spinosaurus mirabilis – mirabilis means “astonishing” in Latin – because it had an unusual, tall crest on its head.
This find was so sudden and amazing, it was really emotional for our team. I’ll forever cherish the moment in camp when we crowded around a laptop to look at the new species for the first time, after one member of our team generated 3D digital models of the bones we found to assemble the skull, on solar power in the middle of the Sahara. That’s when the significance of the discovery really registered.
Sereno and his colleagues published their findings in the peer-reviewed journal Nature on February 19, 2026.
University of Chicago paleontologist Paul Sereno led the team that excavated and identified the new spinosaur, Spinosaurus mirabilis. He poses here with the skull cast. Image via Keith Ladzinski/ University of Chicago. Used with permission.
This Spinosaurus was a dramatic-looking creature!
Spinosaurs lived 100 to 94 million years ago in present-day Africa. Until now, researchers only recognized one species, Spinosaurus aegyptiacus. Scientists found those fossils at sites that were once coastal habitats when the animals were alive. Therefore, they thought these dinosaurs could be aquatic or semi-aquatic, capable of hunting for fish in the sea. But the degree to which they took to the water was not clear.
These dinosaurs had upward-projecting bones from their backs, creating stunning sail-like features. The animals likely used the sail for display, and it may have even regulated body temperature. In addition, S. aegyptiacus had a long skull similar to crocodiles, optimized for catching fish.
These unusual dinosaurs became extinct about 94 million years ago, due to a rapid rise in sea level and climate change.
A video of Paul Sereno and his team in the field, in Niger, in 2022. Provided by the University of Chicago.
Finding a new Spinosaurus in Niger
In 2019, a local man in the Republic of Niger led Sereno and his team to a site called Jenguebi that had large fossil bones. Due to the long journey back to camp, the team only had time to grab a few fossils, including teeth and jawbones. But they did not yet know it was a new dinosaur species.
In 2022, Sereno returned to Jenguebi with a larger team. During that expedition, they found more fossils there, as well as many more at a site called Iguidi. In all, they were able to collect incomplete skeletons from several individuals, all of them immature spinosaurs that had not reached adulthood.
He said:
The local people we work with are my lifelong friends, now including the man who led us to Jenguebi and the astonishing spinosaur. They understand the importance of what we’re doing together, for science and for their country.
Dan Vidal, a member of Sereno’s team, with Abdoul Nasser, a guide who led them to the Jenguebi fossil site in 2019. There, they found the first Spinosaurus mirabilis fossils. Image via Alhadji Akamaya/ University of Chicago. Used with permission.
Spinosaurus mirabilis
During the 2022 expedition, as they examined their finds, the team realized they had discovered a species new to science. This spinosaur had an unusually tall head crest. Also, the teeth arrangement in its jaw was a bit different from that of S. aegyptiacus.
The new spinosaur had a crest at the top of the skull that the researchers described as scimitar-shaped. That’s a short sword with a curved blade that becomes broader at its tip. In addition, internal vascular canals and the surface texture of the crest suggested it was once coated in keratin. That’s a fibrous protein found in hair, nails and horns. Moreover, they speculated this crest might have been brightly colored.
Ana Lázaro, a member of Sereno’s 2022 expedition to Niger, holds the most complete head crest found for Spinosaurus mirabilis. Image via Alvaro Simarro/ University of Chicago. Used with permission.
S. mirabilis’ jaws were quite formidable, similar to those of S. aegyptiacus. It had interdigitating upper and lower tooth rows. In other words, the teeth in the lower jaw extended outward. Meanwhile, the lower jaw teeth interlocked with those in the upper jaw. This is a feature that exists in many fish-eating animals in the fossil record, such as ichthyosaurs, pterosaurs and some crocodiles.
These are 2 skull casts of spinosaurs. At the top is the newly discovered Spinosaurus mirabilis, and below it is the previously known Spinosaurus aegyptiacus from North Africa. Image via Keith Ladzinski/ University of Chicago. Used with permission.
The bones they collected all came from subadult animals. Therefore, it’s hard to determine the size of an adult S. mirabilis. However, they were able to establish that the individual initially used to describe the species – the holotype – was about 26 feet (8 meters) long.
New clues to how spinosaurs lived
The previously known S. aegyptiacus was found in North Africa, at locations that were once coastal habitat when the animals were alive. Scientists wondered if spinosaurs were fully aquatic and able to dive for prey. But there was considerable debate about it.
However, this new discovery paints a different picture of how spinosaurs may have lived. About 95 million years ago, Jenguebi was 310 miles (500 km) from the coastline. Iguidi was even further away, about 620 miles (1,000 km). That’s pretty far inland from the ocean.
Moreover, the scientists also found fossils from two long-necked dinosaurs (sauropods) near the S. mirabilis fossils. In fact, all those bones had been buried in river sediment. This indicated that S. mirabilis and the other dinosaurs lived in close proximity, in an inland forested habitat that had a network of rivers. Therefore, the researchers think S. mirabilis hunted for fish in shallow water.
Sereno commented:
I envision this dinosaur as a kind of ‘hell heron’ that had no problem wading on its sturdy legs into two meters of water but probably spent most of its time stalking shallower traps for the many large fish of the day.
Artist’s illustration of a pair of Spinosaurus mirabilis fighting over the carcass of an ancient fish on the bank of a river in an inland forest, about 95 million years ago. Image via Dani Navarro/ University of Chicago. Used with permission.
Bottom line: Scientists discovered a previously unknown 95-million-year-old spinosaur species, Spinosaurus mirabilis, in Niger, Africa, which had a tall crest on its head.
From a Northern Hemisphere location, face generally northward to find the Big Dipper asterism in the constellation Ursa Major. Look mid-evening or later in February, earlier in March. Draw an imaginary line diagonally through the bowl of the Big Dipper, from the star Megrez through the star Merak. You are going in the direction opposite of the Big Dipper’s handle. You’ll see 2 stars noticeable for being bright and close together: Castor and Pollux.
Castor, in the constellation Gemini the Twins, shines with a bright white light. That’s in contrast to the golden glow of its brother star in Gemini, Pollux. Despite being labeled as twins, Castor and Pollux are not gravitationally bound. Yet Castor is gravitationally bound into a multiple system of its own. In fact, it’s six stars in one!
Castor’s other designation is Alpha Geminorum. And usually an alpha star is the brightest in its constellation. But Castor is 2nd-brightest in Gemini, however, after Pollux (or Beta Geminorum).
Castor is about 51 light-years away. Meanwhile, Pollux is only 34 light-years away. So Pollux is closer to us. And their distances also show Pollux and Castor aren’t gravitationally bound, but only near each other along our line of sight.
And in 2026 Jupiter is nearby
The constellation Gemini the Twins is high in the February evening sky. And in February 2026 – and for the next few months – the bright planet Jupiter is near the 2 brightest stars of Gemini. These stars are golden Pollux and white Castor. Pollux is the slightly brighter one. But Jupiter outshines them both! Chart via EarthSky.
Castor is a complex star system
Castor is three pairs of binary stars – six stars in all – in a complex dance around a common center of mass.
Even a fairly small telescope will show Castor as two stars. In addition, you might glimpse a much-fainter star nearby, too; it’s also part of the Castor system. Each of these three stars – called Castor A, B and C – is also double. Telescopes don’t show them as double directly. But a spectroscope – which splits starlight into its component colors – reveals each of the three stars as double.
The two larger visible components in the Castor system are hot A-type stars. On the other hand, the smaller components are cool, M-type red dwarf stars.
Altogether, the mass of all six stars is, very roughly, about six times that of our sun.
The star Castor is a system of six gravitationally bound stars. There are 3 pairs of stars, each pair orbiting their common center of mass. The Castor A pair and the Castor B pair mutually orbit their common center of mass. These 4 stars and the Castor C pair orbit their common center of mass. Image via NASA/ JPL-Caltech/ Nicholas Beeson/ Wikimedia Commons.
Visualizing the separation of the stars
This figure shows the orbit hierarchy of Castor’s star system, along with each of their orbital periods and separation from each other. Castor Aa and Ba orbit each other, and each have their own stellar companion, Ab and Bb, respectively. Castor C, composed of the binary pair Ca and Cb, is farther away and orbits around Castor Aa/Ab and Ba/Bb. Image via Wikipedia.
Another way to find the Twins
Northern Hemisphere skywatchers can find Castor and Pollux using the Big Dipper as a guide, as shown on the chart at the top of this post. And, from anywhere on the globe, you can use the constellation Orion the Hunter (see chart below) to find the the twins.
Star-hop from Orion to the “twin” stars Castor and Pollux by drawing an imaginary line from Orion’s bright star Rigel through its bright star Betelgeuse. Then, extend this line about three times the distance between these two stars.
A line from Rigel to Betelgeuse in the easy-to-see constellation Orion points to Castor and Pollux.
Greek mythology of Castor and Pollux
The reason for the name Castor is unclear. There appears to be no specific connection with a beaver, which is what the word means in Latin.
However, there is much mythology associated with these two stars, typically in conjunction with each other. Generally in mythology they are twins. In Greek mythology, Pollux is immortal, the son of Zeus, and Castor is mortal, the son of King Tyndareus of Sparta.
So, they were really half-brothers rather than true twins, with a common mother in Queen Leda. Their conception and birth was a complicated and unlikely affair, though, with their mother succumbing to both Zeus (disguised as a swan) and King Tyndareus on the same night. The resulting birth gave us not only Castor and Pollux but also their sister, Helen of Troy.
According to legend, Castor and Pollux sailed among the Argonauts with Jason in search of the Golden Fleece. By most accounts, Castor was killed in battle and Pollux could not bear to live without him. Zeus allowed Pollux to spend every other day in Olympus with the gods, and the rest of the time in the underworld with his brother.
To honor the brothers’ devotion, Zeus placed their constellation in the sky as a remembrance.
Castor and Pollux, the Gemini twins, as depicted in Urania’s Mirror, a set of constellation cards from around 1825. Image via Adam Cuerdon/ Wikipedia.
Other stories surrounding the stars
While in many cultures they were the Twins, in India they were the Horsemen, and in Phoenicia they were the two gazelles or two kid-goats. Likewise, early Christians sometimes called them David and Jonathan, while the early Arabian stargazers knew them as two peacocks.
Perhaps the most unexpected interpretation for the Twins (along with the rest of Gemini) was as a “pile of bricks” as reported by Richard Hinckley Allen. Apparently the pile of bricks stood for the foundation of Rome, and in that context Castor and Pollux were associated with Romulus and Remus, the city’s legendary twin founders.
Additionally, the twin stars represent Yin and Yang, the contrasts and complements of life, in Chinese culture. In all of these cases, they represent two of something.
Indeed, you’ll see why if you find these two stars in the night sky.
Castor’s position is RA: 07h 34m 36s, Dec: +31° 53′ 19″
Bottom line: The star Castor, which appears as one of two bright stars in the constellation Gemini the Twins, is actually a six-star system.
From a Northern Hemisphere location, face generally northward to find the Big Dipper asterism in the constellation Ursa Major. Look mid-evening or later in February, earlier in March. Draw an imaginary line diagonally through the bowl of the Big Dipper, from the star Megrez through the star Merak. You are going in the direction opposite of the Big Dipper’s handle. You’ll see 2 stars noticeable for being bright and close together: Castor and Pollux.
Castor, in the constellation Gemini the Twins, shines with a bright white light. That’s in contrast to the golden glow of its brother star in Gemini, Pollux. Despite being labeled as twins, Castor and Pollux are not gravitationally bound. Yet Castor is gravitationally bound into a multiple system of its own. In fact, it’s six stars in one!
Castor’s other designation is Alpha Geminorum. And usually an alpha star is the brightest in its constellation. But Castor is 2nd-brightest in Gemini, however, after Pollux (or Beta Geminorum).
Castor is about 51 light-years away. Meanwhile, Pollux is only 34 light-years away. So Pollux is closer to us. And their distances also show Pollux and Castor aren’t gravitationally bound, but only near each other along our line of sight.
And in 2026 Jupiter is nearby
The constellation Gemini the Twins is high in the February evening sky. And in February 2026 – and for the next few months – the bright planet Jupiter is near the 2 brightest stars of Gemini. These stars are golden Pollux and white Castor. Pollux is the slightly brighter one. But Jupiter outshines them both! Chart via EarthSky.
Castor is a complex star system
Castor is three pairs of binary stars – six stars in all – in a complex dance around a common center of mass.
Even a fairly small telescope will show Castor as two stars. In addition, you might glimpse a much-fainter star nearby, too; it’s also part of the Castor system. Each of these three stars – called Castor A, B and C – is also double. Telescopes don’t show them as double directly. But a spectroscope – which splits starlight into its component colors – reveals each of the three stars as double.
The two larger visible components in the Castor system are hot A-type stars. On the other hand, the smaller components are cool, M-type red dwarf stars.
Altogether, the mass of all six stars is, very roughly, about six times that of our sun.
The star Castor is a system of six gravitationally bound stars. There are 3 pairs of stars, each pair orbiting their common center of mass. The Castor A pair and the Castor B pair mutually orbit their common center of mass. These 4 stars and the Castor C pair orbit their common center of mass. Image via NASA/ JPL-Caltech/ Nicholas Beeson/ Wikimedia Commons.
Visualizing the separation of the stars
This figure shows the orbit hierarchy of Castor’s star system, along with each of their orbital periods and separation from each other. Castor Aa and Ba orbit each other, and each have their own stellar companion, Ab and Bb, respectively. Castor C, composed of the binary pair Ca and Cb, is farther away and orbits around Castor Aa/Ab and Ba/Bb. Image via Wikipedia.
Another way to find the Twins
Northern Hemisphere skywatchers can find Castor and Pollux using the Big Dipper as a guide, as shown on the chart at the top of this post. And, from anywhere on the globe, you can use the constellation Orion the Hunter (see chart below) to find the the twins.
Star-hop from Orion to the “twin” stars Castor and Pollux by drawing an imaginary line from Orion’s bright star Rigel through its bright star Betelgeuse. Then, extend this line about three times the distance between these two stars.
A line from Rigel to Betelgeuse in the easy-to-see constellation Orion points to Castor and Pollux.
Greek mythology of Castor and Pollux
The reason for the name Castor is unclear. There appears to be no specific connection with a beaver, which is what the word means in Latin.
However, there is much mythology associated with these two stars, typically in conjunction with each other. Generally in mythology they are twins. In Greek mythology, Pollux is immortal, the son of Zeus, and Castor is mortal, the son of King Tyndareus of Sparta.
So, they were really half-brothers rather than true twins, with a common mother in Queen Leda. Their conception and birth was a complicated and unlikely affair, though, with their mother succumbing to both Zeus (disguised as a swan) and King Tyndareus on the same night. The resulting birth gave us not only Castor and Pollux but also their sister, Helen of Troy.
According to legend, Castor and Pollux sailed among the Argonauts with Jason in search of the Golden Fleece. By most accounts, Castor was killed in battle and Pollux could not bear to live without him. Zeus allowed Pollux to spend every other day in Olympus with the gods, and the rest of the time in the underworld with his brother.
To honor the brothers’ devotion, Zeus placed their constellation in the sky as a remembrance.
Castor and Pollux, the Gemini twins, as depicted in Urania’s Mirror, a set of constellation cards from around 1825. Image via Adam Cuerdon/ Wikipedia.
Other stories surrounding the stars
While in many cultures they were the Twins, in India they were the Horsemen, and in Phoenicia they were the two gazelles or two kid-goats. Likewise, early Christians sometimes called them David and Jonathan, while the early Arabian stargazers knew them as two peacocks.
Perhaps the most unexpected interpretation for the Twins (along with the rest of Gemini) was as a “pile of bricks” as reported by Richard Hinckley Allen. Apparently the pile of bricks stood for the foundation of Rome, and in that context Castor and Pollux were associated with Romulus and Remus, the city’s legendary twin founders.
Additionally, the twin stars represent Yin and Yang, the contrasts and complements of life, in Chinese culture. In all of these cases, they represent two of something.
Indeed, you’ll see why if you find these two stars in the night sky.
Castor’s position is RA: 07h 34m 36s, Dec: +31° 53′ 19″
Bottom line: The star Castor, which appears as one of two bright stars in the constellation Gemini the Twins, is actually a six-star system.
Draw an imaginary line from 2 bright stars in the easy-to-see constellation Orion the Hunter to star-hop to the “twin” stars Castor and Pollux. The line goes from Orion’s bright star Rigel through its bright star Betelgeuse and extends about 3 times the distance between them. Castor and Pollux are noticeable for being bright and close together on the sky’s dome. Pollux is brighter than Castor. Chart via EarthSky.
Like a pair of twins, two stars shine prominently in the evening skies in February each year. They are Pollux and Castor in the constellation Gemini the Twins. Pollux, also known as Beta Geminorum, is slightly brighter than Castor. It shines with a golden glow while Castor appears whiter. Pollux is the 17th brightest star in Earth’s night sky.
Pollux and Castor are noticeable for being bright and close together. That’s likely how the early stargazers came to identify them as twins. And it’ll be helpful to you, too, when you’re trying to spot these two stars in our night sky.
Pollux is relatively close to us at 34 light-years away.
You can use the easy-to-see constellation Orion to find Castor and Pollux, as shown on the chart above.
And in 2026, bright Jupiter is nearby
The constellation Gemini the Twins is high in the February evening sky. And in February 2026 – and for the next few months – the bright planet Jupiter is near the 2 brightest stars of Gemini. These stars are golden Pollux and white Castor. Pollux is the slightly brighter one. But Jupiter outshines them both! Chart via EarthSky.
Another way to find them
There are two good ways to find Pollux and Castor. From a Northern Hemisphere location face generally northward to find the Big Dipper asterism in the constellation Ursa Major. Draw an imaginary line diagonally through the bowl of the Big Dipper, from the star Megrez through the star Merak. You are going in the direction opposite to the Big Dipper’s handle.
Draw an imaginary line diagonally through the Big Dipper” rel=”noopener” target=”_blank”>Big Dipper’s bowl to locate Castor and Pollux.
Science of Pollux
Pollux is classified as a K0 IIIb star. The K0 means that it is somewhat cooler than the sun, with a surface color that is a light yellowish orange. Keep in mind that when you look at a star, its color depends significantly on the sensitivity of your eyes, and that color is difficult to discern for most point sources.
Pollux is just under two times the mass of our sun. It’s almost nine times the diameter of our sun. And it’s about 30 times the sun’s brightness in visible light.
Pollux also pumps out a good bit of energy in non-visible infrared radiation. With all forms of radiation counted, Pollux is about 43 times more energetic than our sun.
A large planet, at least two times the mass of Jupiter, was confirmed for Pollux in 2006. The International Astronomical Union announced a proper name for this planet in 2015: Thestias. At 34 light-years away, Thestias is one of the nearest of the more than 6,000 known exoplanets discovered so far.
Thestias moves around Pollux with a period of about 590 Earth days, which is reminiscent of Mars’ orbital period of 687 days. Thestias moves in a nearly circular orbit around its star.
Artist’s concept of the size difference between Pollux and the sun. Image via Omnidoom 999/ Wikimedia Commons.
Why Pollux is Beta
As mentioned above, Pollux is also known as Beta Geminorum. The Greek letter Beta is normally reserved for the 2nd-brightest star in a constellation. But Pollux is brighter than its brother star Castor, which is Gemini’s Alpha star. Being so close together in the sky, Castor and Pollux are easy to compare. If you look, you’ll agree. Pollux is brighter.
It’s possible that one or both stars have altered in brightness since German astronomer Johann Bayer assigned the designation about 300 years ago. Or maybe Bayer sometimes labeled stars in their order of rising times? Castor rises earlier than Pollux as seen from Bayer’s location in Germany. But there’s a geographical dependency here. From some locations south of the equator, Pollux rises first.
Mythology of Pollux and Castor
There is much mythology associated with these two stars, typically only in conjunction with each other. Generally in mythology they are twins. In Greek mythology, Pollux is immortal, the son of Zeus, and Castor is mortal, the son of King Tyndareus of Sparta.
So they were really half-brothers rather than true twins, with a common mother in Queen Leda. Their conception and birth was a complicated and unlikely affair, though, with their mother succumbing to both Zeus (disguised as a swan) and King Tyndareus on the same night. The resulting birth gave us not only Castor and Pollux, but also their sister, Helen of Troy.
Castor and Pollux are later said to have sailed among the Argonauts with Jason in search of the Golden Fleece. By most accounts, Castor was killed in battle and Pollux could not bear to live without him. Pollux begged Zeus to let him die too. Zeus could not grant the gift quite as asked, since Pollux was a god’s son and therefore immortal. But Zeus decreed that Pollux would spend every other day in Olympus with the gods, and the rest of the time in the underworld with his brother.
To honor the brothers’ devotion, Zeus placed their constellation in the sky as a remembrance.
The twin stars in other cultures
While in many cultures they were the Twins, in India they were the Horsemen, and in Phoenicia they were the two gazelles or two kid-goats. Early Christians sometimes called them David and Jonathan, while the early Arabian stargazers knew them as two peacocks.
Perhaps the most unexpected interpretation for the twins (along with the rest of Gemini) was as a “pile of bricks” as reported by Richard Hinckley Allen. Apparently the pile of bricks stood for the foundation of Rome, and in that context Castor and Pollux were associated with Romulus and Remus, the city’s legendary twin founders.
It’s said that in China they were associated with Yin and Yang, the contrasts and complements of life. In all of these cases, they represent two of something.
You’ll see why if you find these two stars in the night sky.
Pollux’s position is RA: 7h 45m 20s, dec: +28° 01′ 35″.
Castor and Pollux, the Gemini twins, as depicted in Urania’s Mirror, a set of constellation cards from around 1825. Image via Adam Cuerdon/ Wikipedia.
Bottom line: Pollux, aka Beta Geminorum, is the slightly brighter “twin” of Castor in the constellation Gemini the Twins.
Draw an imaginary line from 2 bright stars in the easy-to-see constellation Orion the Hunter to star-hop to the “twin” stars Castor and Pollux. The line goes from Orion’s bright star Rigel through its bright star Betelgeuse and extends about 3 times the distance between them. Castor and Pollux are noticeable for being bright and close together on the sky’s dome. Pollux is brighter than Castor. Chart via EarthSky.
Like a pair of twins, two stars shine prominently in the evening skies in February each year. They are Pollux and Castor in the constellation Gemini the Twins. Pollux, also known as Beta Geminorum, is slightly brighter than Castor. It shines with a golden glow while Castor appears whiter. Pollux is the 17th brightest star in Earth’s night sky.
Pollux and Castor are noticeable for being bright and close together. That’s likely how the early stargazers came to identify them as twins. And it’ll be helpful to you, too, when you’re trying to spot these two stars in our night sky.
Pollux is relatively close to us at 34 light-years away.
You can use the easy-to-see constellation Orion to find Castor and Pollux, as shown on the chart above.
And in 2026, bright Jupiter is nearby
The constellation Gemini the Twins is high in the February evening sky. And in February 2026 – and for the next few months – the bright planet Jupiter is near the 2 brightest stars of Gemini. These stars are golden Pollux and white Castor. Pollux is the slightly brighter one. But Jupiter outshines them both! Chart via EarthSky.
Another way to find them
There are two good ways to find Pollux and Castor. From a Northern Hemisphere location face generally northward to find the Big Dipper asterism in the constellation Ursa Major. Draw an imaginary line diagonally through the bowl of the Big Dipper, from the star Megrez through the star Merak. You are going in the direction opposite to the Big Dipper’s handle.
Draw an imaginary line diagonally through the Big Dipper” rel=”noopener” target=”_blank”>Big Dipper’s bowl to locate Castor and Pollux.
Science of Pollux
Pollux is classified as a K0 IIIb star. The K0 means that it is somewhat cooler than the sun, with a surface color that is a light yellowish orange. Keep in mind that when you look at a star, its color depends significantly on the sensitivity of your eyes, and that color is difficult to discern for most point sources.
Pollux is just under two times the mass of our sun. It’s almost nine times the diameter of our sun. And it’s about 30 times the sun’s brightness in visible light.
Pollux also pumps out a good bit of energy in non-visible infrared radiation. With all forms of radiation counted, Pollux is about 43 times more energetic than our sun.
A large planet, at least two times the mass of Jupiter, was confirmed for Pollux in 2006. The International Astronomical Union announced a proper name for this planet in 2015: Thestias. At 34 light-years away, Thestias is one of the nearest of the more than 6,000 known exoplanets discovered so far.
Thestias moves around Pollux with a period of about 590 Earth days, which is reminiscent of Mars’ orbital period of 687 days. Thestias moves in a nearly circular orbit around its star.
Artist’s concept of the size difference between Pollux and the sun. Image via Omnidoom 999/ Wikimedia Commons.
Why Pollux is Beta
As mentioned above, Pollux is also known as Beta Geminorum. The Greek letter Beta is normally reserved for the 2nd-brightest star in a constellation. But Pollux is brighter than its brother star Castor, which is Gemini’s Alpha star. Being so close together in the sky, Castor and Pollux are easy to compare. If you look, you’ll agree. Pollux is brighter.
It’s possible that one or both stars have altered in brightness since German astronomer Johann Bayer assigned the designation about 300 years ago. Or maybe Bayer sometimes labeled stars in their order of rising times? Castor rises earlier than Pollux as seen from Bayer’s location in Germany. But there’s a geographical dependency here. From some locations south of the equator, Pollux rises first.
Mythology of Pollux and Castor
There is much mythology associated with these two stars, typically only in conjunction with each other. Generally in mythology they are twins. In Greek mythology, Pollux is immortal, the son of Zeus, and Castor is mortal, the son of King Tyndareus of Sparta.
So they were really half-brothers rather than true twins, with a common mother in Queen Leda. Their conception and birth was a complicated and unlikely affair, though, with their mother succumbing to both Zeus (disguised as a swan) and King Tyndareus on the same night. The resulting birth gave us not only Castor and Pollux, but also their sister, Helen of Troy.
Castor and Pollux are later said to have sailed among the Argonauts with Jason in search of the Golden Fleece. By most accounts, Castor was killed in battle and Pollux could not bear to live without him. Pollux begged Zeus to let him die too. Zeus could not grant the gift quite as asked, since Pollux was a god’s son and therefore immortal. But Zeus decreed that Pollux would spend every other day in Olympus with the gods, and the rest of the time in the underworld with his brother.
To honor the brothers’ devotion, Zeus placed their constellation in the sky as a remembrance.
The twin stars in other cultures
While in many cultures they were the Twins, in India they were the Horsemen, and in Phoenicia they were the two gazelles or two kid-goats. Early Christians sometimes called them David and Jonathan, while the early Arabian stargazers knew them as two peacocks.
Perhaps the most unexpected interpretation for the twins (along with the rest of Gemini) was as a “pile of bricks” as reported by Richard Hinckley Allen. Apparently the pile of bricks stood for the foundation of Rome, and in that context Castor and Pollux were associated with Romulus and Remus, the city’s legendary twin founders.
It’s said that in China they were associated with Yin and Yang, the contrasts and complements of life. In all of these cases, they represent two of something.
You’ll see why if you find these two stars in the night sky.
Pollux’s position is RA: 7h 45m 20s, dec: +28° 01′ 35″.
Castor and Pollux, the Gemini twins, as depicted in Urania’s Mirror, a set of constellation cards from around 1825. Image via Adam Cuerdon/ Wikipedia.
Bottom line: Pollux, aka Beta Geminorum, is the slightly brighter “twin” of Castor in the constellation Gemini the Twins.
Watch EarthSky’s Deborah Byrd and Marcy Curran discuss the February 28 planet parade and what you can see in the night sky.
February 28 planet parade: Here’s what you can really see
The internet has been full of memes and claims that there will be a spectacular lineup of six visible planets on February 28. But, as is often the case with online chatter, some of it is not accurate. So here’s what you can really see in the sky on the evening of February 28.
As soon as the sun sets, the first thing you’ll probably notice in the sky is the moon. It will already have risen in the east and it will be big and bright, at almost 93% full. It’s just a few days away from full moon, on March 3, when there will be a total lunar eclipse. But on the evening of February 28, it’s not yet full, and there’s a bright “star” shining higher in the sky above the moon. That star is really the planet Jupiter.
While Jupiter and the moon make a pretty scene, you’ll have to tear your eyes away and look toward the western horizon where the sun has recently set. There you’ll find a cluster of planets that will also soon be setting. Venus is the brightest, but it’s also currently close to the horizon. So it will be competing with the evening glow of twilight.
Mercury is dimmer and a bit north of Venus. Next is Saturn, a bit higher above the horizon. So it will be visible as the sky gets darker. But to see any of these three, you must have a flat horizon with no buildings, trees or other obstructions blocking your view.
So that’s only four planets, and really just one of them is easy to see. There are two other planets in the sky that night as well. Uranus is close to the pretty star cluster known as the Pleiades, while Neptune is not far from Saturn. But both of these planets require optical aid to see.
Star charts for the planetary parade
Why do posts on social media point to February 28? It’s a bit of a mystery, because the planets have been in these same general positions for weeks. Planets don’t move that quickly. Perhaps this date is popular because the moon is at one end of the line of planets, near bright Jupiter.
Check out the charts below to find where the planets are, in case you want to hunt them down yourself. And keep up with where the moon and planets are every night with EarthSky’s visible planets and night sky guide.
As seen from across Earth toward the end of February – about 40 minutes after sunset – the bright planet Jupiter will be in the east. Very low in the west, just above the horizon, is Venus, Mercury and Saturn. Note that these planets lie along the path the sun travels in the daytime (the green line on our chart, or the ecliptic). Chart via EarthSky.It’s true that there are 6 planets in the sky after sunset in mid-to-late February. But 3 (Venus, Mercury and Saturn) are hiding near the sunset’s glow, and 2 (Uranus and Neptune) require optical aid to see. Yet you can see them if you have patience, persistence, optical aid, a detailed star chart and a location with a clear view to the western horizon. And anyone can spot bright Jupiter, not far from the famous constellation Orion. Chart via EarthSky.
Bottom line: Rumors of a February 28 planet parade are sweeping the internet. Will you be able to see six planets in a line? Get the details here.
Watch EarthSky’s Deborah Byrd and Marcy Curran discuss the February 28 planet parade and what you can see in the night sky.
February 28 planet parade: Here’s what you can really see
The internet has been full of memes and claims that there will be a spectacular lineup of six visible planets on February 28. But, as is often the case with online chatter, some of it is not accurate. So here’s what you can really see in the sky on the evening of February 28.
As soon as the sun sets, the first thing you’ll probably notice in the sky is the moon. It will already have risen in the east and it will be big and bright, at almost 93% full. It’s just a few days away from full moon, on March 3, when there will be a total lunar eclipse. But on the evening of February 28, it’s not yet full, and there’s a bright “star” shining higher in the sky above the moon. That star is really the planet Jupiter.
While Jupiter and the moon make a pretty scene, you’ll have to tear your eyes away and look toward the western horizon where the sun has recently set. There you’ll find a cluster of planets that will also soon be setting. Venus is the brightest, but it’s also currently close to the horizon. So it will be competing with the evening glow of twilight.
Mercury is dimmer and a bit north of Venus. Next is Saturn, a bit higher above the horizon. So it will be visible as the sky gets darker. But to see any of these three, you must have a flat horizon with no buildings, trees or other obstructions blocking your view.
So that’s only four planets, and really just one of them is easy to see. There are two other planets in the sky that night as well. Uranus is close to the pretty star cluster known as the Pleiades, while Neptune is not far from Saturn. But both of these planets require optical aid to see.
Star charts for the planetary parade
Why do posts on social media point to February 28? It’s a bit of a mystery, because the planets have been in these same general positions for weeks. Planets don’t move that quickly. Perhaps this date is popular because the moon is at one end of the line of planets, near bright Jupiter.
Check out the charts below to find where the planets are, in case you want to hunt them down yourself. And keep up with where the moon and planets are every night with EarthSky’s visible planets and night sky guide.
As seen from across Earth toward the end of February – about 40 minutes after sunset – the bright planet Jupiter will be in the east. Very low in the west, just above the horizon, is Venus, Mercury and Saturn. Note that these planets lie along the path the sun travels in the daytime (the green line on our chart, or the ecliptic). Chart via EarthSky.It’s true that there are 6 planets in the sky after sunset in mid-to-late February. But 3 (Venus, Mercury and Saturn) are hiding near the sunset’s glow, and 2 (Uranus and Neptune) require optical aid to see. Yet you can see them if you have patience, persistence, optical aid, a detailed star chart and a location with a clear view to the western horizon. And anyone can spot bright Jupiter, not far from the famous constellation Orion. Chart via EarthSky.
Bottom line: Rumors of a February 28 planet parade are sweeping the internet. Will you be able to see six planets in a line? Get the details here.
Astronomers use the term orbital resonance to describe the way planets can gravitationally affect each other when their orbits line up in a regular way. Here, we see 2 planets in a 2:1 orbital resonance. In other words, for every 2 times the inner planet goes around its star, the outer planet goes around once. Image via Amitchell125/ Wikimedia Commons (CC-BY-SA 4.0).
Planets orbit their parent stars while separated by enormous distances. In our solar system, planets are like grains of sand in a region the size of a football field. The time that planets take to orbit their suns has no specific relationship to each other.
But sometimes, their orbits display striking patterns. For example, astronomers studying six planets orbiting a star 100 light-years away have found that they orbit their star with an almost rhythmic beat, in perfect synchrony. Each pair of planets completes their orbits in times that are the ratios of whole numbers, allowing the planets to align and exert a gravitational push and pull on the other during their orbit.
This type of gravitational alignment is called orbital resonance, and it’s like a harmony between distant planets.
I’m an astronomer who studies and writes about cosmology. Researchers have discovered over 6,000 exoplanets in the past 30 years, and their extraordinary diversity continues to surprise astronomers.
Harmony of the spheres
Greek mathematician Pythagoras discovered the principles of musical harmony 2,500 years ago by analyzing the sounds of blacksmiths’ hammers and plucked strings.
He believed mathematics was at the heart of the natural world. He proposed that the sun, moon and planets each emit unique hums based on their orbital properties. Pythagoras thought this “music of the spheres” would be imperceptible to the human ear.
Four hundred years ago, Johannes Kepler picked up this idea. He proposed that musical intervals and harmonies described the motions of the six known planets at the time.
To Kepler, the solar system had two basses, Jupiter and Saturn; a tenor, Mars; two altos, Venus and Earth; and a soprano, Mercury. These roles reflected how long it took each planet to orbit the sun, lower speeds for the outer planets and higher speeds for the inner planets.
He called the book he wrote on these mathematical relationships The Harmony of the World. While these ideas have some similarities to the concept of orbital resonance, planets don’t actually make sounds, since sound can’t travel through the vacuum of space.
Orbital resonance
Resonance happens when planets or moons have orbital periods that are ratios of whole numbers. The orbital period is the time taken for a planet to make one complete circuit of the star. So, for example, two planets orbiting a star would be in a 2:1 resonance when one planet takes twice as long as the other to orbit the star. Resonance is seen in only 5% of planetary systems.
Orbital resonance, as seen with Jupiter’s moons, happens when planetary bodies’ orbits line up. For example, Io orbits Jupiter four times in the time it takes Europa to orbit twice and Ganymede to orbit once. Image via WolfmanSF/ Wikimedia Commons (CC0 1.0).
In the solar system, Neptune and Pluto are in a 3:2 resonance. There’s also a triple resonance, 4:2:1, among Jupiter’s three moons Ganymede, Europa and Io. In the time it takes Ganymede to orbit Jupiter, Europa orbits twice and Io orbits four times. Resonances occur naturally, when planets happen to have orbital periods that are the ratio of whole numbers.
The relation to music
Musical intervals describe the relationship between two musical notes. In the musical analogy, important musical intervals based on ratios of frequencies are the fourth, 4:3, the fifth, 3:2, and the octave, 2:1. Anyone who plays the guitar or the piano might recognize these intervals.
Musical intervals can be used to create scales and harmony.
What does orbital resonance do?
Orbital resonances can change how gravity influences two bodies, causing them to speed up, slow down, stabilize on their orbital path and sometimes have their orbits disrupted.
Think of pushing a child on a swing. A planet and a swing both have a natural frequency. Give the child a push that matches the swing motion and they’ll get a boost. They’ll also get a boost if you push them every other time they’re in that position, or every third time. But push them at random times, sometimes with the motion of the swing and sometimes against, and they get no boost.
Orbital resonance can cause planets or asteroids to speed up or start to wobble.
For planets, the boost can keep them continuing on their orbital paths, but it’s much more likely to disrupt their orbits.
Exoplanet resonance
Exoplanets, or planets outside the solar system, show striking examples of resonance, not just between two objects but also between resonant “chains” involving three or more objects.
The star Gliese 876 has three planets with orbit period ratios of 4:2:1, just like Jupiter’s three moons. Kepler 223 has four planets with ratios of 8:6:4:3.
The red dwarf Kepler 80 has five planets with ratios of 9:6:4:3:2, and TOI 178 has six planets, of which five are in a resonant chain with ratios of 18:9:6:4:3.
TRAPPIST-1 is the record holder. It has seven Earth-like planets, two of which might be habitable, with orbit ratios of 24:15:9:6:4:3:2.
The newest example of a resonant chain is the HD 110067 system. It’s about 100 light-years away and has six sub-Neptune planets, a common type of exoplanet, with orbit ratios of 54:36:24:16:12:9. The discovery is interesting because most resonance chains are unstable and disappear over time.
Despite these examples, resonant chains are rare, and only 1% of all planetary systems display them. Astronomers think that planets form in resonance, but small gravitational nudges from passing stars and wandering planets erase the resonance over time. With HD 110067, the resonant chain has survived for billions of years, offering a rare and pristine view of the system as it was when it formed.
With exoplanets, sonification can convey the mathematical relationships of their orbits. Astronomers at the European Southern Observatory created what they call music of the spheres for the TOI 178 system by associating a sound on a pentatonic scale to each of the five planets.
Music from planetary orbits, created by astronomers at the European Southern Observatory.
A similar musical translation has been done for the TRAPPIST-1 system, with the orbital frequencies scaled up by a factor of 212 million to bring them into audible range.
Astronomers have also created a sonification for the HD 110067 system. People may not agree on whether these renditions sound like actual music, but it’s inspiring to see Pythagoras’ ideas realized after 2,500 years.
Bottom line: What is orbital resonance? It’s a precise dance between heavenly bodies when their orbits line up, causing them to have specific synchronicities.
Astronomers use the term orbital resonance to describe the way planets can gravitationally affect each other when their orbits line up in a regular way. Here, we see 2 planets in a 2:1 orbital resonance. In other words, for every 2 times the inner planet goes around its star, the outer planet goes around once. Image via Amitchell125/ Wikimedia Commons (CC-BY-SA 4.0).
Planets orbit their parent stars while separated by enormous distances. In our solar system, planets are like grains of sand in a region the size of a football field. The time that planets take to orbit their suns has no specific relationship to each other.
But sometimes, their orbits display striking patterns. For example, astronomers studying six planets orbiting a star 100 light-years away have found that they orbit their star with an almost rhythmic beat, in perfect synchrony. Each pair of planets completes their orbits in times that are the ratios of whole numbers, allowing the planets to align and exert a gravitational push and pull on the other during their orbit.
This type of gravitational alignment is called orbital resonance, and it’s like a harmony between distant planets.
I’m an astronomer who studies and writes about cosmology. Researchers have discovered over 6,000 exoplanets in the past 30 years, and their extraordinary diversity continues to surprise astronomers.
Harmony of the spheres
Greek mathematician Pythagoras discovered the principles of musical harmony 2,500 years ago by analyzing the sounds of blacksmiths’ hammers and plucked strings.
He believed mathematics was at the heart of the natural world. He proposed that the sun, moon and planets each emit unique hums based on their orbital properties. Pythagoras thought this “music of the spheres” would be imperceptible to the human ear.
Four hundred years ago, Johannes Kepler picked up this idea. He proposed that musical intervals and harmonies described the motions of the six known planets at the time.
To Kepler, the solar system had two basses, Jupiter and Saturn; a tenor, Mars; two altos, Venus and Earth; and a soprano, Mercury. These roles reflected how long it took each planet to orbit the sun, lower speeds for the outer planets and higher speeds for the inner planets.
He called the book he wrote on these mathematical relationships The Harmony of the World. While these ideas have some similarities to the concept of orbital resonance, planets don’t actually make sounds, since sound can’t travel through the vacuum of space.
Orbital resonance
Resonance happens when planets or moons have orbital periods that are ratios of whole numbers. The orbital period is the time taken for a planet to make one complete circuit of the star. So, for example, two planets orbiting a star would be in a 2:1 resonance when one planet takes twice as long as the other to orbit the star. Resonance is seen in only 5% of planetary systems.
Orbital resonance, as seen with Jupiter’s moons, happens when planetary bodies’ orbits line up. For example, Io orbits Jupiter four times in the time it takes Europa to orbit twice and Ganymede to orbit once. Image via WolfmanSF/ Wikimedia Commons (CC0 1.0).
In the solar system, Neptune and Pluto are in a 3:2 resonance. There’s also a triple resonance, 4:2:1, among Jupiter’s three moons Ganymede, Europa and Io. In the time it takes Ganymede to orbit Jupiter, Europa orbits twice and Io orbits four times. Resonances occur naturally, when planets happen to have orbital periods that are the ratio of whole numbers.
The relation to music
Musical intervals describe the relationship between two musical notes. In the musical analogy, important musical intervals based on ratios of frequencies are the fourth, 4:3, the fifth, 3:2, and the octave, 2:1. Anyone who plays the guitar or the piano might recognize these intervals.
Musical intervals can be used to create scales and harmony.
What does orbital resonance do?
Orbital resonances can change how gravity influences two bodies, causing them to speed up, slow down, stabilize on their orbital path and sometimes have their orbits disrupted.
Think of pushing a child on a swing. A planet and a swing both have a natural frequency. Give the child a push that matches the swing motion and they’ll get a boost. They’ll also get a boost if you push them every other time they’re in that position, or every third time. But push them at random times, sometimes with the motion of the swing and sometimes against, and they get no boost.
Orbital resonance can cause planets or asteroids to speed up or start to wobble.
For planets, the boost can keep them continuing on their orbital paths, but it’s much more likely to disrupt their orbits.
Exoplanet resonance
Exoplanets, or planets outside the solar system, show striking examples of resonance, not just between two objects but also between resonant “chains” involving three or more objects.
The star Gliese 876 has three planets with orbit period ratios of 4:2:1, just like Jupiter’s three moons. Kepler 223 has four planets with ratios of 8:6:4:3.
The red dwarf Kepler 80 has five planets with ratios of 9:6:4:3:2, and TOI 178 has six planets, of which five are in a resonant chain with ratios of 18:9:6:4:3.
TRAPPIST-1 is the record holder. It has seven Earth-like planets, two of which might be habitable, with orbit ratios of 24:15:9:6:4:3:2.
The newest example of a resonant chain is the HD 110067 system. It’s about 100 light-years away and has six sub-Neptune planets, a common type of exoplanet, with orbit ratios of 54:36:24:16:12:9. The discovery is interesting because most resonance chains are unstable and disappear over time.
Despite these examples, resonant chains are rare, and only 1% of all planetary systems display them. Astronomers think that planets form in resonance, but small gravitational nudges from passing stars and wandering planets erase the resonance over time. With HD 110067, the resonant chain has survived for billions of years, offering a rare and pristine view of the system as it was when it formed.
With exoplanets, sonification can convey the mathematical relationships of their orbits. Astronomers at the European Southern Observatory created what they call music of the spheres for the TOI 178 system by associating a sound on a pentatonic scale to each of the five planets.
Music from planetary orbits, created by astronomers at the European Southern Observatory.
A similar musical translation has been done for the TRAPPIST-1 system, with the orbital frequencies scaled up by a factor of 212 million to bring them into audible range.
Astronomers have also created a sonification for the HD 110067 system. People may not agree on whether these renditions sound like actual music, but it’s inspiring to see Pythagoras’ ideas realized after 2,500 years.
Bottom line: What is orbital resonance? It’s a precise dance between heavenly bodies when their orbits line up, causing them to have specific synchronicities.
