Longest days accompany the December solstice

Sundial at Adler Planetarium in Chicago. A sundial can be used to measure the interval from one solar noon to the next. Earth’s longest days, from noon to noon, happen in December. Image via Wikimedia Commons/ CC BY-SA 4.0.

What is a day? You might casually talk about a day as a period of daylight. Or you could measure a day in relationship to the sun or the stars. Astronomers use the term solar day to describe a day relative to the sun. A solar day is the time from one solar noon – one local noon or high noon – to the next. It’s the interval between successive days as marked by the sun’s highest point in our sky. If you look at a day in that way, you can say that the longest days of the year come each year around the December solstice … no matter where you live on the globe.

Available now! 2025 EarthSky lunar calendar. A unique and beautiful poster-sized calendar showing phases of the moon every night of the year! And it makes a great gift.

The longest days are in December

What? Isn’t the shortest day for the Northern Hemisphere at the December solstice? Yes, it is, if we are talking about the period of daylight.

But, we’re talking about the (approximately) 24-hour interval from one solar noon to the next. In December, a day – one rotation of Earth relative to the noonday sun – is about half a minute longer than the average 24 hours, for the entire globe.

Keep in mind that the clocks on our walls don’t measure the true length of a day, as measured from solar noon to solar noon. To measure that sort of day, you’d need a sundial. A sundial will tell you the precise moment of local solar noon, when the sun reaches its highest point in the sky each day.

Days are always longer – as measured from one solar noon to the next – than 24 hours around the solstices, and less than 24 hours around the equinoxes.

Why are the days longer in December?

The days are at their longest now – for the entire globe – because we’re closer to the sun on the December solstice than we are at the June solstice. Earth’s perihelion – closest point to the sun – always comes in early January. So when we’re closest to the sun, our planet is moving a little faster than average in its orbit. That means our planet is traveling through space a little farther than average each day.

The result is that Earth has to rotate a little more on its axis for the sun to return to its noontime position. That effect lengthens the solar day by about eight seconds. In contrast, at aphelion, when the Earth is moving slower in its orbit, the solar day is about seven seconds shorter.

There’s another effect that happens during both the winter and summer solstices that increases the solar day by 21 seconds. It’s due to the way the sun moves mostly eastward, in relation to the stars, during solstices. Therefore, when the sun rises and moves up in the sky, it takes a bit longer to reach high noon from the previous day’s high noon.

For the winter solstice, the combined effects of these two phenomena increase the solar day by about 29 seconds.

Half a minute longer doesn’t sound like much, but the difference adds up. For instance, two weeks before the December solstice, noontime comes about seven minutes earlier by the clock than on the December solstice. And then two weeks after the December solstice, noon comes about seven minutes later by the clock than on the December solstice itself.

Sunrises and sunsets

Because the clock and sun are most out of sync right now, some befuddling phenomena cause people to scratch their heads at this time of the year. In the Northern Hemisphere, the year’s earliest sunsets precede the December winter solstice. And the year’s latest sunrises come after the December winter solstice. So the earliest sunsets came earlier in December for most of us; and the latest sunrises won’t come until early January.

In the Southern Hemisphere, the year’s earliest sunrises precede the December summer solstice, and the year’s latest sunsets come after the December summer solstice.

The fact that we’re closest to the sun in early January also means that Northern Hemisphere winter (Southern Hemisphere summer) is the shortest of the four seasons. Read more about the shortest season here.

However, at the same time … It’s the season of bountifully long solar days.

Visit Sunrise Sunset Calendars to find out the clock time for solar noon at your locality; remember to check the Solar noon box.

View larger. | This figure-8 shape is called an analemma. It shows the position of the sun at the same time each day, on successive days of a year. Read about analemmas at Wikipedia. Image via Matthew Chin in Hong Kong. Used with permission.

Bottom line: As measured from one solar noon to the next, December has the longest days – the longest interval from the sun’s highest point on one day to its highest point on the next day – for the entire Earth. And that’s true, no matter where you live on the globe.

A planisphere is virtually indispensable for beginning stargazers. Order your EarthSky Planisphere today!

The post Longest days accompany the December solstice first appeared on EarthSky.

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Sundial at Adler Planetarium in Chicago. A sundial can be used to measure the interval from one solar noon to the next. Earth’s longest days, from noon to noon, happen in December. Image via Wikimedia Commons/ CC BY-SA 4.0.

What is a day? You might casually talk about a day as a period of daylight. Or you could measure a day in relationship to the sun or the stars. Astronomers use the term solar day to describe a day relative to the sun. A solar day is the time from one solar noon – one local noon or high noon – to the next. It’s the interval between successive days as marked by the sun’s highest point in our sky. If you look at a day in that way, you can say that the longest days of the year come each year around the December solstice … no matter where you live on the globe.

Available now! 2025 EarthSky lunar calendar. A unique and beautiful poster-sized calendar showing phases of the moon every night of the year! And it makes a great gift.

The longest days are in December

What? Isn’t the shortest day for the Northern Hemisphere at the December solstice? Yes, it is, if we are talking about the period of daylight.

But, we’re talking about the (approximately) 24-hour interval from one solar noon to the next. In December, a day – one rotation of Earth relative to the noonday sun – is about half a minute longer than the average 24 hours, for the entire globe.

Keep in mind that the clocks on our walls don’t measure the true length of a day, as measured from solar noon to solar noon. To measure that sort of day, you’d need a sundial. A sundial will tell you the precise moment of local solar noon, when the sun reaches its highest point in the sky each day.

Days are always longer – as measured from one solar noon to the next – than 24 hours around the solstices, and less than 24 hours around the equinoxes.

Why are the days longer in December?

The days are at their longest now – for the entire globe – because we’re closer to the sun on the December solstice than we are at the June solstice. Earth’s perihelion – closest point to the sun – always comes in early January. So when we’re closest to the sun, our planet is moving a little faster than average in its orbit. That means our planet is traveling through space a little farther than average each day.

The result is that Earth has to rotate a little more on its axis for the sun to return to its noontime position. That effect lengthens the solar day by about eight seconds. In contrast, at aphelion, when the Earth is moving slower in its orbit, the solar day is about seven seconds shorter.

There’s another effect that happens during both the winter and summer solstices that increases the solar day by 21 seconds. It’s due to the way the sun moves mostly eastward, in relation to the stars, during solstices. Therefore, when the sun rises and moves up in the sky, it takes a bit longer to reach high noon from the previous day’s high noon.

For the winter solstice, the combined effects of these two phenomena increase the solar day by about 29 seconds.

Half a minute longer doesn’t sound like much, but the difference adds up. For instance, two weeks before the December solstice, noontime comes about seven minutes earlier by the clock than on the December solstice. And then two weeks after the December solstice, noon comes about seven minutes later by the clock than on the December solstice itself.

Sunrises and sunsets

Because the clock and sun are most out of sync right now, some befuddling phenomena cause people to scratch their heads at this time of the year. In the Northern Hemisphere, the year’s earliest sunsets precede the December winter solstice. And the year’s latest sunrises come after the December winter solstice. So the earliest sunsets came earlier in December for most of us; and the latest sunrises won’t come until early January.

In the Southern Hemisphere, the year’s earliest sunrises precede the December summer solstice, and the year’s latest sunsets come after the December summer solstice.

The fact that we’re closest to the sun in early January also means that Northern Hemisphere winter (Southern Hemisphere summer) is the shortest of the four seasons. Read more about the shortest season here.

However, at the same time … It’s the season of bountifully long solar days.

Visit Sunrise Sunset Calendars to find out the clock time for solar noon at your locality; remember to check the Solar noon box.

View larger. | This figure-8 shape is called an analemma. It shows the position of the sun at the same time each day, on successive days of a year. Read about analemmas at Wikipedia. Image via Matthew Chin in Hong Kong. Used with permission.

Bottom line: As measured from one solar noon to the next, December has the longest days – the longest interval from the sun’s highest point on one day to its highest point on the next day – for the entire Earth. And that’s true, no matter where you live on the globe.

A planisphere is virtually indispensable for beginning stargazers. Order your EarthSky Planisphere today!

The post Longest days accompany the December solstice first appeared on EarthSky.

from EarthSky https://ift.tt/fVrxDWl

How to catch a supernova explosion before it happens

Artist’s concept of Eta Carinae’s Great Eruption in 1843. This star underwent a great eruption but not a full-blown supernova. Is it possible to catch a supernova before it happens? Image via Hubblesite.

• How do we know if a star is about to go supernova? Some stars give no warning while others have slowly brightened or flickered before exploding.
• Not all stars erupt in a true supernova. Other stars, like Eta Carinae, have great eruptions that don’t blow themselves entirely apart.
• Stars in multiple star systems might interact with each other in a way that lets astronomers know that one of the stars is about to explode. The Vera C. Rubin Observatory will help search for supernova precursors, so astronomers can catch more stars in the act of erupting.

By Seán Brennan, Stockholm University

How to catch a supernova explosion before it happens

Stars are born, live and die in spectacular ways, with their deaths marked by one of the biggest known explosions in the universe. Like a campfire needs wood to keep burning, a star relies on nuclear fusion – primarily using hydrogen as fuel – to generate energy and counteract the crushing force of its own gravity.

The 2025 EarthSky Lunar Calendar is now available! A unique and beautiful poster-sized calendar. Makes a great gift. Get yours today!

But when the fuel runs out, the outward pressure vanishes, and the star collapses under its own weight. It falls inward at nearly the speed of light, crashing into the core and rebounding outward. Within seconds, the star violently blows itself apart. It hurls stellar debris into space at speeds thousands of times faster than the most powerful rocket ever built. This is a supernova explosion.

Astronomers aim to understand what types of stars produce different kinds of explosions. Do more massive stars result in brighter explosions? What happens if a star is surrounded by dust and gas when it explodes?

Finding a star that’s ready to blow

While we have simulations modeling a star’s death, they are difficult to validate. Observing a star’s behavior in real-time before the explosion could help answer these questions … but finding such a star is no easy task.

Scientists already do this with eruptions on Earth. Volcanologists monitor volcanoes, measuring changes in activity to predict an upcoming eruption. For example, in March 1980, Mount St. Helens in the U.S. began to show some precursor events, such as seismic activity, and dozens of steam eruptions ejecting ash and gas into the atmosphere.

Two months later, an earthquake triggered the largest landslide ever recorded, releasing built-up pressure in the magma chamber, resulting in a catastrophic eruption that devastated an area of over 230 square miles (600 square km).

Plumes of steam, gas, and ash often occurred at Mount St. Helens in the early 1980s. Image via USGS/ Wikipedia (public domain).

Pre-supernova eruptions

Massive stars – larger than around 10 times the mass of the sun – can do the same thing, albeit at much larger scales. In 2009, astronomers observed a bright event 65 million light-years away that on first impression resembled a supernova explosion.

Dubbed SN 2009ip, the explosion did not brighten as expected. Scientists reclassified it shortly after discovery as a “supernova impostor,” a giant eruption which ultimately does not destroy the star.

Over the next three years, the star underwent many rapid “flickering” events, a bit like quickly turning on and off a light bulb. Finally, in 2012, an unexpected supernova occurred. Scientists are still studying the evolution of the supernova explosion to this day. And what exactly happened from 2009 to 2012 remains a mystery.

Our team published a recent paper in Astronomy and Astrophysics about a peculiar star in the Virgo Cluster, coincidentally also 65 million light-years away. Unlike SN 2009ip, the star lacked hydrogen and consisted primarily of helium. The star slowly increased its brightness for over five years – akin to slowly turning on a bulb using a dimmer switch – before it went supernova.

That supernova, SN 2023fyq, provided astronomers with a rare opportunity. Observatories worldwide and in space captured the first light from the supernova explosion, known as shock breakout, largely due to the daily monitoring of the precursor activity.

Multiple stars and supernovas

This precursor activity offers an exciting chance to uncover the mysteries of supernova explosions, shedding light on both the conditions leading up to and following these cosmic events.

The underlying cause of this pre-supernova activity remains unclear. Scientists think an isolated massive star does not experience such rapid fluctuations in brightness. In the final moments of a star’s life, its core undergoes rapid evolution, desperately attempting to counteract the crushing force of gravity with its dwindling fuel reserves.

However, the star is so large at this stage that any activity in the core doesn’t have enough time to reach the surface. Observing these dramatic changes, occurring so close to the star’s demise, present a significant challenge to current theories.

One compelling hypothesis points to the interaction of multiple stars. Stars are born in dense clouds of gas and dust where multiple stars can form in close proximity. Neighboring stars may interact gravitationally with one another, exchanging material as they orbit each other.

This mass transfer could account for the changes in brightness observed in SN 2009ip before its explosion and the hydrogen deficiency we saw in SN 2023fyq. The companion involved might be another massive star, or perhaps a more exotic object, such as a black hole.

We know not all eruptions will not end in a supernova explosion. For example, in the 1840s, Eta Carinae – a star 100 times larger than the sun – experienced the Great Eruption. It launched 30 times the sun’s mass into space. Although this was an extremely energetic explosion, the massive star was not destroyed.

Watching for signals of a supernova

Do all stars announce their departure? We aren’t sure. We have observed seemingly normal supernovas with precursor eruptions, thanks in part to deep observations catching the faint precursor activity.

In 2025, the Vera C. Rubin Observatory, equipped with the world’s largest camera, will begin to study these events. At 3,200 megapixels, it is over 40 times more sensitive than cameras we have available on Earth. The observatory provides us the opportunity to search for fainter precursor activity.

At Stockholm University, our team is currently using telescopes from the European Southern Observatory and the Zwicky Transient Facility. This includes the Nordic Optical Telescope in La Palma, Spain, and the Very Large Telescope at Cerro Paranal in the Atacama Desert of northern Chile. We use them to identify the signs that indicate a star is nearing the end of its life.

By recognizing these signals, we can alert the scientific community and be ready to watch as a star experiences its final, dramatic moments.

Seán Brennan, Postdoctoral Reseracher in the Supernova and Explosive Transient Group, Stockholm University.

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

Bottom line: Astronomers are looking for signals that a star is about to go supernova. Some stars give no warning while others have slowly brightened before exploding. The new Vera C. Rubin Observatory coming online will aid in the search.

Read more: Betelgeuse is dimming again. When will it explode?

The post How to catch a supernova explosion before it happens first appeared on EarthSky.

from EarthSky https://ift.tt/rjH8hw1

Artist’s concept of Eta Carinae’s Great Eruption in 1843. This star underwent a great eruption but not a full-blown supernova. Is it possible to catch a supernova before it happens? Image via Hubblesite.

• How do we know if a star is about to go supernova? Some stars give no warning while others have slowly brightened or flickered before exploding.
• Not all stars erupt in a true supernova. Other stars, like Eta Carinae, have great eruptions that don’t blow themselves entirely apart.
• Stars in multiple star systems might interact with each other in a way that lets astronomers know that one of the stars is about to explode. The Vera C. Rubin Observatory will help search for supernova precursors, so astronomers can catch more stars in the act of erupting.

By Seán Brennan, Stockholm University

How to catch a supernova explosion before it happens

Stars are born, live and die in spectacular ways, with their deaths marked by one of the biggest known explosions in the universe. Like a campfire needs wood to keep burning, a star relies on nuclear fusion – primarily using hydrogen as fuel – to generate energy and counteract the crushing force of its own gravity.

The 2025 EarthSky Lunar Calendar is now available! A unique and beautiful poster-sized calendar. Makes a great gift. Get yours today!

But when the fuel runs out, the outward pressure vanishes, and the star collapses under its own weight. It falls inward at nearly the speed of light, crashing into the core and rebounding outward. Within seconds, the star violently blows itself apart. It hurls stellar debris into space at speeds thousands of times faster than the most powerful rocket ever built. This is a supernova explosion.

Astronomers aim to understand what types of stars produce different kinds of explosions. Do more massive stars result in brighter explosions? What happens if a star is surrounded by dust and gas when it explodes?

Finding a star that’s ready to blow

While we have simulations modeling a star’s death, they are difficult to validate. Observing a star’s behavior in real-time before the explosion could help answer these questions … but finding such a star is no easy task.

Scientists already do this with eruptions on Earth. Volcanologists monitor volcanoes, measuring changes in activity to predict an upcoming eruption. For example, in March 1980, Mount St. Helens in the U.S. began to show some precursor events, such as seismic activity, and dozens of steam eruptions ejecting ash and gas into the atmosphere.

Two months later, an earthquake triggered the largest landslide ever recorded, releasing built-up pressure in the magma chamber, resulting in a catastrophic eruption that devastated an area of over 230 square miles (600 square km).

Plumes of steam, gas, and ash often occurred at Mount St. Helens in the early 1980s. Image via USGS/ Wikipedia (public domain).

Pre-supernova eruptions

Massive stars – larger than around 10 times the mass of the sun – can do the same thing, albeit at much larger scales. In 2009, astronomers observed a bright event 65 million light-years away that on first impression resembled a supernova explosion.

Dubbed SN 2009ip, the explosion did not brighten as expected. Scientists reclassified it shortly after discovery as a “supernova impostor,” a giant eruption which ultimately does not destroy the star.

Over the next three years, the star underwent many rapid “flickering” events, a bit like quickly turning on and off a light bulb. Finally, in 2012, an unexpected supernova occurred. Scientists are still studying the evolution of the supernova explosion to this day. And what exactly happened from 2009 to 2012 remains a mystery.

Our team published a recent paper in Astronomy and Astrophysics about a peculiar star in the Virgo Cluster, coincidentally also 65 million light-years away. Unlike SN 2009ip, the star lacked hydrogen and consisted primarily of helium. The star slowly increased its brightness for over five years – akin to slowly turning on a bulb using a dimmer switch – before it went supernova.

That supernova, SN 2023fyq, provided astronomers with a rare opportunity. Observatories worldwide and in space captured the first light from the supernova explosion, known as shock breakout, largely due to the daily monitoring of the precursor activity.

Multiple stars and supernovas

This precursor activity offers an exciting chance to uncover the mysteries of supernova explosions, shedding light on both the conditions leading up to and following these cosmic events.

The underlying cause of this pre-supernova activity remains unclear. Scientists think an isolated massive star does not experience such rapid fluctuations in brightness. In the final moments of a star’s life, its core undergoes rapid evolution, desperately attempting to counteract the crushing force of gravity with its dwindling fuel reserves.

However, the star is so large at this stage that any activity in the core doesn’t have enough time to reach the surface. Observing these dramatic changes, occurring so close to the star’s demise, present a significant challenge to current theories.

One compelling hypothesis points to the interaction of multiple stars. Stars are born in dense clouds of gas and dust where multiple stars can form in close proximity. Neighboring stars may interact gravitationally with one another, exchanging material as they orbit each other.

This mass transfer could account for the changes in brightness observed in SN 2009ip before its explosion and the hydrogen deficiency we saw in SN 2023fyq. The companion involved might be another massive star, or perhaps a more exotic object, such as a black hole.

We know not all eruptions will not end in a supernova explosion. For example, in the 1840s, Eta Carinae – a star 100 times larger than the sun – experienced the Great Eruption. It launched 30 times the sun’s mass into space. Although this was an extremely energetic explosion, the massive star was not destroyed.

Watching for signals of a supernova

Do all stars announce their departure? We aren’t sure. We have observed seemingly normal supernovas with precursor eruptions, thanks in part to deep observations catching the faint precursor activity.

In 2025, the Vera C. Rubin Observatory, equipped with the world’s largest camera, will begin to study these events. At 3,200 megapixels, it is over 40 times more sensitive than cameras we have available on Earth. The observatory provides us the opportunity to search for fainter precursor activity.

At Stockholm University, our team is currently using telescopes from the European Southern Observatory and the Zwicky Transient Facility. This includes the Nordic Optical Telescope in La Palma, Spain, and the Very Large Telescope at Cerro Paranal in the Atacama Desert of northern Chile. We use them to identify the signs that indicate a star is nearing the end of its life.

By recognizing these signals, we can alert the scientific community and be ready to watch as a star experiences its final, dramatic moments.

Seán Brennan, Postdoctoral Reseracher in the Supernova and Explosive Transient Group, Stockholm University.

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

Bottom line: Astronomers are looking for signals that a star is about to go supernova. Some stars give no warning while others have slowly brightened before exploding. The new Vera C. Rubin Observatory coming online will aid in the search.

Read more: Betelgeuse is dimming again. When will it explode?

The post How to catch a supernova explosion before it happens first appeared on EarthSky.

from EarthSky https://ift.tt/rjH8hw1

2024 December solstice: All you need to know

In 2024, the December solstice falls at 9:21 UTC on December 21 (3:21 a.m. CST). Long nights, short days, for the Northern Hemisphere. Short nights, long days, for our friends south of the equator. No matter where you live on Earth’s globe, the solstice is your signal to celebrate seasonal change.

The December solstice marks the sun’s southernmost point in the sky, for all of Earth, for this year. It comes at 9:21 UTC (3:21 a.m. CST) on December 21. Though no world body has decreed it, we in the Northern Hemisphere will celebrate the first day of winter at this solstice. For us, it heralds the longest nights and shortest days of our year.

Meanwhile, people in the Southern Hemisphere will celebrate the first day of summer at this solstice. For them it marks the shortest nights and longest days.

After this solstice, the sun will begin moving northward in the sky again. It’s fun to track the northward movement of the sunsets on your horizon with pieces of tape on a window, or just by noticing the shifting sunset point from your favorite spot to observe.

View larger. | Ian Hennes in Medicine Hat, Alberta, Canada, created this solargram between a June solstice and a December solstice. It shows the path of the sun during that time period. Thank you, Ian! Used with permission.

View at EarthSky Community Photos.| José Palma in Mina São Domingos, Portugal, shared this solargram. He wrote: “The objective of this ultra-long exposure was to show in a single image the variation of the path of the sun and its altitude, between the summer solstice and the winter solstice, resulting in 183 days – 4,392 hours – of exposure.” Read more about this image. Thank you, José.

What is a solstice?

The earliest people on Earth knew that the sun’s path across the sky, the length of daylight, and the location of the sunrise and sunset all shifted in a regular way throughout the year. They built monuments such as Stonehenge in England and at Machu Picchu in Peru to follow the sun’s yearly progress.

Today, we picture the solstice from the vantage point of space, and we know that the solstice is an astronomical event. It’s caused by the tilt of Earth’s axis and by its orbital motion around the sun.

Earth doesn’t orbit upright. Instead, it’s tilted on its axis by 23.5 degrees. Through the year, this tilt causes Earth’s Northern and Southern Hemispheres to trade places in receiving the sun’s light and warmth most directly. It’s this tilt, not our distance from the sun, that causes winter and summer.

In fact, we’re closest to – not farthest from – the sun at the turn of every new year. At the same time, we in the Northern Hemisphere are moving into winter. That’s because the Northern Hemisphere leans farthest away from the sun for the year around this time.

On the day of the December solstice, the sun takes its farthest pass south on the globe. Image via Jecowa/ Wikimedia Commons (CC BY-SA 3.0).

Why isn’t the earliest sunset on the shortest day?

The December solstice marks the shortest day of the year in the Northern Hemisphere and longest day in the Southern Hemisphere. But the earliest sunset – or earliest sunrise if you’re south of the equator – happens before the December solstice.

Instead of focusing on the time of sunset or sunrise, the key is in what is called true solar noon, which is the time of day that the sun reaches its highest point in its journey across your sky.

In early December, true solar noon comes nearly 10 minutes earlier by the clock than it does at the solstice around December 21. With true noon coming later on the solstice, so will the sunrise and sunset times.

It’s this discrepancy between clock time and sun time that causes the Northern Hemisphere’s earliest sunset and the Southern Hemisphere’s earliest sunrise to precede the December solstice.

The precise date of the earliest sunset (or earliest sunrise) depends on your latitude. But the sequence is always the same: earliest sunset, shortest day at the solstice, latest sunrise around early January. Or, for the Southern Hemisphere now, earliest sunrise, longest day at the solstice, latest sunset around early July.

And so the cycle continues.

View at EarthSky Community Photos. | Karl Diefenderfer of Quakertown, Pennsylvania, wrote: “Vibrant winter’s solstice sunrise.” Thank you, Karl! By the way, the December solstice starts the year’s shortest season.

The poles at the December solstice

At the December solstice, Earth is positioned so the sun stays below the North Pole’s horizon. Meanwhile, the sun is up 24 hours a day at the South Pole.

All locations south of the equator have day lengths greater than 12 hours.

All locations north of the equator have day lengths shorter than 12 hours.

Where should I look to see signs of the December solstice in nature?

Everywhere.

For all of Earth’s creatures, nothing is so fundamental as the length of daylight. After all, the sun is the ultimate source of all light and warmth on Earth.

In the Northern Hemisphere, you’ll notice late dawns and early sunsets, the low arc of the sun across the sky each day, and how low the sun appears in the sky at local noon. Look at your noontime shadow, too. Around the time of the December solstice, it’s your longest noontime shadow of the year.

In the Southern Hemisphere, it’s opposite. Dawn comes early, dusk comes late, the sun is high, and it’s your shortest noontime shadow of the year.

Satellite views of Earth on the solstices and equinoxes. We are at the December solstice now. Read more about this image. Images via NASA Earth Observatory.

Bottom line: The 2024 December solstice takes place on December 21, at 9:21 UTC. It marks the Northern Hemisphere’s shortest day (first day of winter) and Southern Hemisphere’s longest day (first day of summer). Happy solstice to all!

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The post 2024 December solstice: All you need to know first appeared on EarthSky.

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In 2024, the December solstice falls at 9:21 UTC on December 21 (3:21 a.m. CST). Long nights, short days, for the Northern Hemisphere. Short nights, long days, for our friends south of the equator. No matter where you live on Earth’s globe, the solstice is your signal to celebrate seasonal change.

The December solstice marks the sun’s southernmost point in the sky, for all of Earth, for this year. It comes at 9:21 UTC (3:21 a.m. CST) on December 21. Though no world body has decreed it, we in the Northern Hemisphere will celebrate the first day of winter at this solstice. For us, it heralds the longest nights and shortest days of our year.

Meanwhile, people in the Southern Hemisphere will celebrate the first day of summer at this solstice. For them it marks the shortest nights and longest days.

After this solstice, the sun will begin moving northward in the sky again. It’s fun to track the northward movement of the sunsets on your horizon with pieces of tape on a window, or just by noticing the shifting sunset point from your favorite spot to observe.

View larger. | Ian Hennes in Medicine Hat, Alberta, Canada, created this solargram between a June solstice and a December solstice. It shows the path of the sun during that time period. Thank you, Ian! Used with permission.

View at EarthSky Community Photos.| José Palma in Mina São Domingos, Portugal, shared this solargram. He wrote: “The objective of this ultra-long exposure was to show in a single image the variation of the path of the sun and its altitude, between the summer solstice and the winter solstice, resulting in 183 days – 4,392 hours – of exposure.” Read more about this image. Thank you, José.

What is a solstice?

The earliest people on Earth knew that the sun’s path across the sky, the length of daylight, and the location of the sunrise and sunset all shifted in a regular way throughout the year. They built monuments such as Stonehenge in England and at Machu Picchu in Peru to follow the sun’s yearly progress.

Today, we picture the solstice from the vantage point of space, and we know that the solstice is an astronomical event. It’s caused by the tilt of Earth’s axis and by its orbital motion around the sun.

Earth doesn’t orbit upright. Instead, it’s tilted on its axis by 23.5 degrees. Through the year, this tilt causes Earth’s Northern and Southern Hemispheres to trade places in receiving the sun’s light and warmth most directly. It’s this tilt, not our distance from the sun, that causes winter and summer.

In fact, we’re closest to – not farthest from – the sun at the turn of every new year. At the same time, we in the Northern Hemisphere are moving into winter. That’s because the Northern Hemisphere leans farthest away from the sun for the year around this time.

On the day of the December solstice, the sun takes its farthest pass south on the globe. Image via Jecowa/ Wikimedia Commons (CC BY-SA 3.0).

Why isn’t the earliest sunset on the shortest day?

The December solstice marks the shortest day of the year in the Northern Hemisphere and longest day in the Southern Hemisphere. But the earliest sunset – or earliest sunrise if you’re south of the equator – happens before the December solstice.

Instead of focusing on the time of sunset or sunrise, the key is in what is called true solar noon, which is the time of day that the sun reaches its highest point in its journey across your sky.

In early December, true solar noon comes nearly 10 minutes earlier by the clock than it does at the solstice around December 21. With true noon coming later on the solstice, so will the sunrise and sunset times.

It’s this discrepancy between clock time and sun time that causes the Northern Hemisphere’s earliest sunset and the Southern Hemisphere’s earliest sunrise to precede the December solstice.

The precise date of the earliest sunset (or earliest sunrise) depends on your latitude. But the sequence is always the same: earliest sunset, shortest day at the solstice, latest sunrise around early January. Or, for the Southern Hemisphere now, earliest sunrise, longest day at the solstice, latest sunset around early July.

And so the cycle continues.

View at EarthSky Community Photos. | Karl Diefenderfer of Quakertown, Pennsylvania, wrote: “Vibrant winter’s solstice sunrise.” Thank you, Karl! By the way, the December solstice starts the year’s shortest season.

The poles at the December solstice

At the December solstice, Earth is positioned so the sun stays below the North Pole’s horizon. Meanwhile, the sun is up 24 hours a day at the South Pole.

All locations south of the equator have day lengths greater than 12 hours.

All locations north of the equator have day lengths shorter than 12 hours.

Where should I look to see signs of the December solstice in nature?

Everywhere.

For all of Earth’s creatures, nothing is so fundamental as the length of daylight. After all, the sun is the ultimate source of all light and warmth on Earth.

In the Northern Hemisphere, you’ll notice late dawns and early sunsets, the low arc of the sun across the sky each day, and how low the sun appears in the sky at local noon. Look at your noontime shadow, too. Around the time of the December solstice, it’s your longest noontime shadow of the year.

In the Southern Hemisphere, it’s opposite. Dawn comes early, dusk comes late, the sun is high, and it’s your shortest noontime shadow of the year.

Satellite views of Earth on the solstices and equinoxes. We are at the December solstice now. Read more about this image. Images via NASA Earth Observatory.

Bottom line: The 2024 December solstice takes place on December 21, at 9:21 UTC. It marks the Northern Hemisphere’s shortest day (first day of winter) and Southern Hemisphere’s longest day (first day of summer). Happy solstice to all!

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A daytime moon is up after sunrise

View at EarthSky Community Photos. | Peter Lowenstein caught the daytime moon in its waning gibbous phase from Mutare, Zimbabwe. He said: “Three-quarters of an hour after sunrise, I photographed the daytime moon descending toward the top of a flowering African Tulip (Spathodia campanulta) tree.” Thank you, Peter!

Watch for a daytime moon

This month’s full moon came early on December 15, 2024. So the moon is now in a waning gibbous phase, rising later and later each successive night.

And that means the moon is setting later and later now. It’s setting after sunrise. That’s why the mornings after a full moon are a good time to catch a nearly full daytime moon after sunrise, over your western horizon. Watch for it!

The moon is up in the daytime half of the time. But, because it’s pale against the blue sky, it’s not as noticeable during the day as at night. Still, there are certain windows each month during which the daytime moon is most noticeable.

The coming week presents one of those windows. It’s a good time to watch for a daytime moon.

December 17-18 overnight: Moon passes in front of Mars

The waning gibbous moon will lie close to the red planet Mars on the evening of December 17, 2024. At 9 UTC on the morning of December 18, 2024, the moon will occult – or pass in front of – Mars, visible from parts of Canada, Greenland, eastern Russia and Alaska and other locations. Others will see Mars close to the moon. Also nearby will be the twin stars of Gemini: Castor and Pollux. They’ll rise several hours after sunset and be visible through dawn. Read Mars updates for 2024, here.

Our charts are mostly set for the northern half of Earth. To see a precise view – and time – from your location, try Stellarium Online.

Chart via EarthSky.

December 19 and 20 mornings: Moon and Regulus

On the mornings of December 19 and 20, 2024, the waning gibbous moon will float near the star Regulus, the brightest star in Leo the Lion. Regulus is the punctuation mark at the bottom of a pattern of stars called the Sickle. Look for them a few hours before dawn. Meet Regulus, Leo the Lion’s Heart.

Read more: What is the Sickle in Leo?

Our charts are mostly set for the northern half of Earth. To see a precise view – and time – from your location, try Stellarium Online.

Chart via EarthSky.

Bottom line: You can easily spot the moon in the morning sky – after sunrise – for a few days after full moon. Look west after the sun comes up!

Donate: Your support means the world to us

Submit your photo to EarthSky here.

The post A daytime moon is up after sunrise first appeared on EarthSky.

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View at EarthSky Community Photos. | Peter Lowenstein caught the daytime moon in its waning gibbous phase from Mutare, Zimbabwe. He said: “Three-quarters of an hour after sunrise, I photographed the daytime moon descending toward the top of a flowering African Tulip (Spathodia campanulta) tree.” Thank you, Peter!

Watch for a daytime moon

This month’s full moon came early on December 15, 2024. So the moon is now in a waning gibbous phase, rising later and later each successive night.

And that means the moon is setting later and later now. It’s setting after sunrise. That’s why the mornings after a full moon are a good time to catch a nearly full daytime moon after sunrise, over your western horizon. Watch for it!

The moon is up in the daytime half of the time. But, because it’s pale against the blue sky, it’s not as noticeable during the day as at night. Still, there are certain windows each month during which the daytime moon is most noticeable.

The coming week presents one of those windows. It’s a good time to watch for a daytime moon.

December 17-18 overnight: Moon passes in front of Mars

The waning gibbous moon will lie close to the red planet Mars on the evening of December 17, 2024. At 9 UTC on the morning of December 18, 2024, the moon will occult – or pass in front of – Mars, visible from parts of Canada, Greenland, eastern Russia and Alaska and other locations. Others will see Mars close to the moon. Also nearby will be the twin stars of Gemini: Castor and Pollux. They’ll rise several hours after sunset and be visible through dawn. Read Mars updates for 2024, here.

Our charts are mostly set for the northern half of Earth. To see a precise view – and time – from your location, try Stellarium Online.

Chart via EarthSky.

December 19 and 20 mornings: Moon and Regulus

On the mornings of December 19 and 20, 2024, the waning gibbous moon will float near the star Regulus, the brightest star in Leo the Lion. Regulus is the punctuation mark at the bottom of a pattern of stars called the Sickle. Look for them a few hours before dawn. Meet Regulus, Leo the Lion’s Heart.

Read more: What is the Sickle in Leo?

Our charts are mostly set for the northern half of Earth. To see a precise view – and time – from your location, try Stellarium Online.

Chart via EarthSky.

Bottom line: You can easily spot the moon in the morning sky – after sunrise – for a few days after full moon. Look west after the sun comes up!

Donate: Your support means the world to us

Submit your photo to EarthSky here.

The post A daytime moon is up after sunrise first appeared on EarthSky.

from EarthSky https://ift.tt/TPl9mpa

Hubble’s closest look at a quasar reveals … weirdness

View larger. | This is the Hubble Space Telescope’s new view of the quasar 3C 273, 2.5 billion light-years away. We can see various filaments and blobs, and the long L-shaped filament on the right in particular. It may be the result of small galaxies being devoured by the central supermassive black hole in the galaxy where the quasar resides. Image via NASA/ ESA/ Bin Ren (Université Côte d’Azur/CNRS)/ Hubblesite.

• Quasars are intensely bright objects in the centers of distant young galaxies. Supermassive black holes power them. Despite being billions of light-years away, their blinding light obscures other details when viewed in telescopes.
• NASA’s Hubble Space Telescope has now taken the closest look yet at a quasar. It is one of the closest quasars, at 2.5 billion light-years from Earth.
• The new images reveal ‘weird things’ such as blobs and filaments near the quasar. One filament in particular is shaped like a giant L.

Looking for a Christmas gift for someone who loves astronomy? The 2025 EarthSky Lunar Calendar is now available. Get yours today!

Close look at a quasar reveals weirdness

Quasars are extremely bright objects in the centers of young galaxies. They are powered by supermassive black holes. Astronomers know of about a million of them now. Being incredibly far away, however, quasars still just look like pinpoints of light. But on December 5, 2024, NASA shared the Hubble Space Telescope’s closest-ever look at a quasar. The new images reveal a lot of “weird things,” including L-shaped filaments and blobs of various sizes.

Hubble took the closest look yet at the first known quasar.

Called 3C 273, this quasar is a brightly glowing galactic center powered by a black hole consuming material.

This helped astronomers open up a new gateway into better understanding quasars: https://t.co/16gBOXtWU5 pic.twitter.com/zvmWCWCWFo

— Hubble (@NASAHubble) December 5, 2024

Closest-ever look at a quasar

Quasars are powerful, emitting thousands of times as much energy as all the stars in a galaxy. However, they are so far away that they still just look like pinpoints of light in telescopes. That’s why astronomers refer to them as quasi-stellar objects. But if you could travel to a quasar, you would see the center of the young galaxy glowing intensely bright. Quasars are powered by supermassive black holes at the centers of these galaxies. They glow brightly as the black holes consume material in the region.

Now, Hubble has taken a new and closer look at a quasar called 3C 273. Astronomer Maarten Schmidt first discovered it in 1963. It is an incredible 2.5 billion light-years from Earth. So, what did Hubble see?

The astronomers said the new views showed a lot of “weird things.” Bin Ren of the Côte d’Azur Observatory and Université Côte d’Azur in Nice, France, said:

We’ve got a few blobs of different sizes, and a mysterious L-shaped filamentary structure. This is all within 16,000 light-years of the black hole.

” /> Here are 2 views of quasar 3C 273 from Hubble. In the bottom image, a coronagraph blocks out the central glare from the middle of the quasar. By doing this, astronomers can see many more fine details. Image via NASA/ ESA/ Bin Ren (Université Côte d’Azur/ CNRS)/ Hubblesite.

Hints of an active environment

Hubble showed hints of significant activity around quasars as early as 1994. The galaxies that hosted the quasars and black holes would collide with other nearby galaxies. As a result, the debris would then fall back onto the black holes, giving them more energy. The black holes, in turn, then continue to power the quasars. So there is a lot of activity around quasars.

Like staring into blinding headlights

Despite the immense distances to quasars, when Hubble looked at 3C 273, it was like staring into the blinding headlights of a car. Indeed, that makes it difficult to see any surrounding details in images.

So Hubble used its Space Telescope Imaging Spectrograph (STIS) instrument as a coronagraph to block out the main glare coming from the quasar. As a result, astronomers could see details eight times closer to the central black hole than previously. And this helped them see details they couldn’t before.

Artist’s concept of pair of quasars – bright, active galaxies – merging. Scientists saw these quasars merging only 900 million years after the Big Bang, in a time period known as the Cosmic Dawn. This makes the merging quasars the most distant merging pair known and the first pair astronomers have seen at the Cosmic Dawn. Image via International Gemini Observatory/ NOIRLab/ NSF/ AURA/ M. Garlick.

Blobs, filaments and jets

The new images revealed just how complex the region around the quasar is.

The researchers saw filaments and blobs around the quasar and black hole. The long L-shaped filament may be the result of small galaxies being devoured by the central supermassive black hole in the galaxy where the quasar resides.

In addition, the observations also provided a better look at a 300,000-light-year-long extragalactic jet of material coming from the quasar. The researchers compared the new images to older ones from Hubble and determined that material in the jet moves faster when it is farther away from the quasar.

As Ren said:

With the fine spatial structures and jet motion, Hubble bridged a gap between the small-scale radio interferometry and large-scale optical imaging observations, and thus we can take an observational step towards a more complete understanding of quasar host morphology. Our previous view was very limited, but Hubble is allowing us to understand the complicated quasar morphology and galactic interactions in detail. In the future, looking further at 3C 273 in infrared light with the James Webb Space Telescope might give us more clues.

More quasars in the early universe

The approximately 1 million known quasars sounds like a lot, and it is. But astronomers say there used to be even more of them earlier in the lifetime of the universe, about 3 billion years ago. At that time, there were more collisions occurring between galaxies. Astronomers also now know that some quasars merged together in the early universe, as early as 900 million years after the Big Bang.

Bottom line: NASA’s Hubble Space Telescope has taken the closest-ever look at a distant quasar. The new images reveal complex blobs and filaments around the quasar.

Via Hubblesite

Read more: 1st pair of merging quasars seen at Cosmic Dawn

Read more: Do galaxy collisions power quasars? Will our Milky Way become a quasar?

The post Hubble’s closest look at a quasar reveals … weirdness first appeared on EarthSky.

from EarthSky https://ift.tt/NFKkbOw

View larger. | This is the Hubble Space Telescope’s new view of the quasar 3C 273, 2.5 billion light-years away. We can see various filaments and blobs, and the long L-shaped filament on the right in particular. It may be the result of small galaxies being devoured by the central supermassive black hole in the galaxy where the quasar resides. Image via NASA/ ESA/ Bin Ren (Université Côte d’Azur/CNRS)/ Hubblesite.

• Quasars are intensely bright objects in the centers of distant young galaxies. Supermassive black holes power them. Despite being billions of light-years away, their blinding light obscures other details when viewed in telescopes.
• NASA’s Hubble Space Telescope has now taken the closest look yet at a quasar. It is one of the closest quasars, at 2.5 billion light-years from Earth.
• The new images reveal ‘weird things’ such as blobs and filaments near the quasar. One filament in particular is shaped like a giant L.

Looking for a Christmas gift for someone who loves astronomy? The 2025 EarthSky Lunar Calendar is now available. Get yours today!

Close look at a quasar reveals weirdness

Quasars are extremely bright objects in the centers of young galaxies. They are powered by supermassive black holes. Astronomers know of about a million of them now. Being incredibly far away, however, quasars still just look like pinpoints of light. But on December 5, 2024, NASA shared the Hubble Space Telescope’s closest-ever look at a quasar. The new images reveal a lot of “weird things,” including L-shaped filaments and blobs of various sizes.

Hubble took the closest look yet at the first known quasar.

Called 3C 273, this quasar is a brightly glowing galactic center powered by a black hole consuming material.

This helped astronomers open up a new gateway into better understanding quasars: https://t.co/16gBOXtWU5 pic.twitter.com/zvmWCWCWFo

— Hubble (@NASAHubble) December 5, 2024

Closest-ever look at a quasar

Quasars are powerful, emitting thousands of times as much energy as all the stars in a galaxy. However, they are so far away that they still just look like pinpoints of light in telescopes. That’s why astronomers refer to them as quasi-stellar objects. But if you could travel to a quasar, you would see the center of the young galaxy glowing intensely bright. Quasars are powered by supermassive black holes at the centers of these galaxies. They glow brightly as the black holes consume material in the region.

Now, Hubble has taken a new and closer look at a quasar called 3C 273. Astronomer Maarten Schmidt first discovered it in 1963. It is an incredible 2.5 billion light-years from Earth. So, what did Hubble see?

The astronomers said the new views showed a lot of “weird things.” Bin Ren of the Côte d’Azur Observatory and Université Côte d’Azur in Nice, France, said:

We’ve got a few blobs of different sizes, and a mysterious L-shaped filamentary structure. This is all within 16,000 light-years of the black hole.

” /> Here are 2 views of quasar 3C 273 from Hubble. In the bottom image, a coronagraph blocks out the central glare from the middle of the quasar. By doing this, astronomers can see many more fine details. Image via NASA/ ESA/ Bin Ren (Université Côte d’Azur/ CNRS)/ Hubblesite.

Hints of an active environment

Hubble showed hints of significant activity around quasars as early as 1994. The galaxies that hosted the quasars and black holes would collide with other nearby galaxies. As a result, the debris would then fall back onto the black holes, giving them more energy. The black holes, in turn, then continue to power the quasars. So there is a lot of activity around quasars.

Like staring into blinding headlights

Despite the immense distances to quasars, when Hubble looked at 3C 273, it was like staring into the blinding headlights of a car. Indeed, that makes it difficult to see any surrounding details in images.

So Hubble used its Space Telescope Imaging Spectrograph (STIS) instrument as a coronagraph to block out the main glare coming from the quasar. As a result, astronomers could see details eight times closer to the central black hole than previously. And this helped them see details they couldn’t before.

Artist’s concept of pair of quasars – bright, active galaxies – merging. Scientists saw these quasars merging only 900 million years after the Big Bang, in a time period known as the Cosmic Dawn. This makes the merging quasars the most distant merging pair known and the first pair astronomers have seen at the Cosmic Dawn. Image via International Gemini Observatory/ NOIRLab/ NSF/ AURA/ M. Garlick.

Blobs, filaments and jets

The new images revealed just how complex the region around the quasar is.

The researchers saw filaments and blobs around the quasar and black hole. The long L-shaped filament may be the result of small galaxies being devoured by the central supermassive black hole in the galaxy where the quasar resides.

In addition, the observations also provided a better look at a 300,000-light-year-long extragalactic jet of material coming from the quasar. The researchers compared the new images to older ones from Hubble and determined that material in the jet moves faster when it is farther away from the quasar.

As Ren said:

With the fine spatial structures and jet motion, Hubble bridged a gap between the small-scale radio interferometry and large-scale optical imaging observations, and thus we can take an observational step towards a more complete understanding of quasar host morphology. Our previous view was very limited, but Hubble is allowing us to understand the complicated quasar morphology and galactic interactions in detail. In the future, looking further at 3C 273 in infrared light with the James Webb Space Telescope might give us more clues.

More quasars in the early universe

The approximately 1 million known quasars sounds like a lot, and it is. But astronomers say there used to be even more of them earlier in the lifetime of the universe, about 3 billion years ago. At that time, there were more collisions occurring between galaxies. Astronomers also now know that some quasars merged together in the early universe, as early as 900 million years after the Big Bang.

Bottom line: NASA’s Hubble Space Telescope has taken the closest-ever look at a distant quasar. The new images reveal complex blobs and filaments around the quasar.

Via Hubblesite

Read more: 1st pair of merging quasars seen at Cosmic Dawn

Read more: Do galaxy collisions power quasars? Will our Milky Way become a quasar?

The post Hubble’s closest look at a quasar reveals … weirdness first appeared on EarthSky.

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Seals ride icebergs strategically to scoot around seas

The 2025 EarthSky lunar calendar makes a great gift. Get yours today!

Scientists have learned that seals ride icebergs strategically to scoot around Earth’s seas. They’ve learned that seal moms in icy parts of Earth’s globe use icebergs shed by glaciers as safe platforms to give birth and care for their young. The moms prefer stable, slower-moving bergs when caring for their newborn seal pups. Then, in the molting season, the moms and the rest of the seal population appear to move to speedier ice near the best foraging grounds. So, seals opt for different types of icebergs, depending on the time of year and their purposes. That’s according to a new study presented at this week’s American Geophysical Union meeting in Washington, D.C.

Lynn Kaluzienski, a postdoctoral fellow at the University of Alaska Southeast, shared her findings about seals and icebergs on December 10, 2024.

She explained how climate change affects glaciers and, consequently, the icebergs and seals that depend on these large blocks of ice in their daily lives.

Mom seals prefer slow, stable icebergs, where they care for their pups. However, seals prefer faster-moving icebergs for feeding. Image via Héloïse Delbos/ Unsplash.

Seals ride icebergs, but which ones?

When an iceberg breaks off from a glacier, its speed and trajectory are affected by many factors, including wind, ocean currents and freshwater runoff flowing from a glacier’s base. For example, a jet of fresh water, called a plume, is more buoyant than salty ocean water in a fjord, which is a inlet to the sea with steep sides or cliffs, often created by glaciers. The freshwater plume brings plankton and fish to the water’s surface, creating a moving buffet that seals can eat while riding aboard the icebergs.

The researchers used remote sensing data to find these plumes and compared them to where icebergs and seals were found during the pupping season in June and molting season in August.

They found that during the pupping season, seals were more likely to be on slow-moving icebergs, with speeds slower than 7 to 8 inches (about 0.2 meters) per second. In contrast, during the molting season, seals were increasingly likely to be on faster-moving icebergs, in or near the plume.

Lynn Kaluzienski led the new study showing that seals ride icebergs to get around the seas. Image via Inspiringgirls.org.

How does climate change affect seals?

The study focused on harbor seals and icebergs in Johns Hopkins Inlet and Glacier, located in Glacier Bay National Park, Alaska. Johns Hopkins is one of the few glaciers on Earth that is getting thicker and flowing into the fjord instead of retreating due to global warming.

This is due, in part, to its terminal moraine. A terminal moraine consists of crushed rock and other sediments blocking the front of the glacier from warmer ocean water, which would increase the rate of melt.

But that wall of sediment reduces the number of icebergs the glacier dumps into the fjord. Fewer icebergs means less habitat for seals, so it’s crucial for researchers to understand how seals use the icebergs they have at their disposal.

New research shows that as glaciers change with the climate, the resulting changes in size, speed and number of icebergs affect the seals’ icy habitat.

Fewer icebergs means less habitat for seals, so it’s crucial for researchers to understand how seals use the icebergs. Image via Jamie Womble/ NPS/ AGU.

Why is this study important?

Kaluzienski, university colleagues, and collaborators from the U.S. National Park Service spent the past few years documenting variations in iceberg and seal distribution in the fjord. They used time-lapse cameras and aerial photographic surveys.

According to Kaluzienski:

Our work provides a direct link between a glacier’s advance and seals’ distribution and behavior. Interdisciplinary studies like this one coupled with long-term monitoring campaigns will be important to understand how climate change will influence tidewater glacier fjord ecosystems in the future.

Kaluzienski added:

Icebergs are found throughout the fjord in regions of fast flow, within eddies, and close to the glacier. We wanted to understand which of these areas seals were using and how this habitat is changing in response to advances at the glacier front and reduction in iceberg numbers.

Climate change affects the glaciers and, consequently, the icebergs and seal habitat. This new study will help better understand seals’ distribution and behavior. Image via Robert Thiemann/ Unsplash.

Bottom line: Surfers love to ride waves, and seals prefer to ride icebergs … but not any iceberg. Depending on the time of year, they prefer steady, slow icebergs and other times fast ones.

Via AGU

Read more: Carnivorous wolves have a sweet tooth: Lifeform of the week

The post Seals ride icebergs strategically to scoot around seas first appeared on EarthSky.

from EarthSky https://ift.tt/OhUwgA3

The 2025 EarthSky lunar calendar makes a great gift. Get yours today!

Scientists have learned that seals ride icebergs strategically to scoot around Earth’s seas. They’ve learned that seal moms in icy parts of Earth’s globe use icebergs shed by glaciers as safe platforms to give birth and care for their young. The moms prefer stable, slower-moving bergs when caring for their newborn seal pups. Then, in the molting season, the moms and the rest of the seal population appear to move to speedier ice near the best foraging grounds. So, seals opt for different types of icebergs, depending on the time of year and their purposes. That’s according to a new study presented at this week’s American Geophysical Union meeting in Washington, D.C.

Lynn Kaluzienski, a postdoctoral fellow at the University of Alaska Southeast, shared her findings about seals and icebergs on December 10, 2024.

She explained how climate change affects glaciers and, consequently, the icebergs and seals that depend on these large blocks of ice in their daily lives.

Mom seals prefer slow, stable icebergs, where they care for their pups. However, seals prefer faster-moving icebergs for feeding. Image via Héloïse Delbos/ Unsplash.

Seals ride icebergs, but which ones?

When an iceberg breaks off from a glacier, its speed and trajectory are affected by many factors, including wind, ocean currents and freshwater runoff flowing from a glacier’s base. For example, a jet of fresh water, called a plume, is more buoyant than salty ocean water in a fjord, which is a inlet to the sea with steep sides or cliffs, often created by glaciers. The freshwater plume brings plankton and fish to the water’s surface, creating a moving buffet that seals can eat while riding aboard the icebergs.

The researchers used remote sensing data to find these plumes and compared them to where icebergs and seals were found during the pupping season in June and molting season in August.

They found that during the pupping season, seals were more likely to be on slow-moving icebergs, with speeds slower than 7 to 8 inches (about 0.2 meters) per second. In contrast, during the molting season, seals were increasingly likely to be on faster-moving icebergs, in or near the plume.

Lynn Kaluzienski led the new study showing that seals ride icebergs to get around the seas. Image via Inspiringgirls.org.

How does climate change affect seals?

The study focused on harbor seals and icebergs in Johns Hopkins Inlet and Glacier, located in Glacier Bay National Park, Alaska. Johns Hopkins is one of the few glaciers on Earth that is getting thicker and flowing into the fjord instead of retreating due to global warming.

This is due, in part, to its terminal moraine. A terminal moraine consists of crushed rock and other sediments blocking the front of the glacier from warmer ocean water, which would increase the rate of melt.

But that wall of sediment reduces the number of icebergs the glacier dumps into the fjord. Fewer icebergs means less habitat for seals, so it’s crucial for researchers to understand how seals use the icebergs they have at their disposal.

New research shows that as glaciers change with the climate, the resulting changes in size, speed and number of icebergs affect the seals’ icy habitat.

Fewer icebergs means less habitat for seals, so it’s crucial for researchers to understand how seals use the icebergs. Image via Jamie Womble/ NPS/ AGU.

Why is this study important?

Kaluzienski, university colleagues, and collaborators from the U.S. National Park Service spent the past few years documenting variations in iceberg and seal distribution in the fjord. They used time-lapse cameras and aerial photographic surveys.

According to Kaluzienski:

Our work provides a direct link between a glacier’s advance and seals’ distribution and behavior. Interdisciplinary studies like this one coupled with long-term monitoring campaigns will be important to understand how climate change will influence tidewater glacier fjord ecosystems in the future.

Kaluzienski added:

Icebergs are found throughout the fjord in regions of fast flow, within eddies, and close to the glacier. We wanted to understand which of these areas seals were using and how this habitat is changing in response to advances at the glacier front and reduction in iceberg numbers.

Climate change affects the glaciers and, consequently, the icebergs and seal habitat. This new study will help better understand seals’ distribution and behavior. Image via Robert Thiemann/ Unsplash.

Bottom line: Surfers love to ride waves, and seals prefer to ride icebergs … but not any iceberg. Depending on the time of year, they prefer steady, slow icebergs and other times fast ones.

Via AGU

Read more: Carnivorous wolves have a sweet tooth: Lifeform of the week

The post Seals ride icebergs strategically to scoot around seas first appeared on EarthSky.

from EarthSky https://ift.tt/OhUwgA3

The Orion Nebula (M42) is a starry nursery

View at EarthSky Community Photos. | Randy Strauss in Papillion, Nebraska, captured this telescopic view of the Orion Nebula on March 4, 2024. Thank you, Randy! The Orion Nebula is one of the most familiar celestial objects, easily visible to the unaided eye below the 3 stars of Orion’s Belt. But it’s a vast stellar nursery, a place where new stars are forming.

The 2025 EarthSky Lunar Calendar is now available! A unique and beautiful poster-sized calendar. Makes a great gift. Get yours today!

Orion the Hunter is the most noticeable of all constellations. The three stars of Orion’s Belt jump out at you as a short, straight row of medium-bright stars, midway between Orion’s two brightest stars, Betelgeuse and Rigel. Once you find the Belt stars, you can also locate the Orion Nebula, otherwise known as M42. When you look at it, you’re gazing toward a stellar nursery, a place where new stars are born.

How to locate the Orion Nebula

If you want to find this famous nebula, first you have to locate the constellation Orion. Fortunately, that’s easy, if you’re looking at the right time of year. The Northern Hemisphere winter months (Southern Hemisphere summer months) are the perfect time to come to know Orion.

First, look for the three medium-bright stars in a short, straight row. These stars represent Orion’s Belt.

Next, if you look closely, you’ll notice a curved line of stars “hanging” from the three Belt stars. These stars represent Orion’s Sword. Look for the Orion Nebula about midway down in the Sword of Orion.

As a general rule, the higher the constellation Orion is in the sky, the easier it is to see the Orion Nebula. From Northern Hemisphere locations, Orion is due south and highest in the sky around midnight in the middle of December. The stars return to the same place in the sky some four minutes earlier each night, or two hours earlier each month. So look for Orion to be highest up around 10 p.m. in mid-January and 8 p.m. in mid-February.

Another time people notice Orion is around the months of August and September, when this constellation appears in the east before dawn.

Orion the Hunter – visible to both hemispheres – rises in the east on December evenings. Chart via Chelynne Campion/ EarthSky.

A globe of luminescent fog

Most nebulae – clouds of interstellar gas and dust – are difficult if not impossible to see with the unaided eye or even binoculars. But the Orion Nebula is in a class nearly all by itself. It’s visible to the unaided eye on a dark, moonless night. To me, it looks like a star encased in a globe of luminescent fog. The star-gazing aficionado Stephen James O’Meara described it as:

… angel’s breath against a frosted sky.

In a dark-sky location, observe the Orion Nebula for yourself to see what it looks like. A backyard telescope, or even binoculars, will do wonders to showcase one of the greatest celestial treasures in the winter sky.

View at EarthSky Community Photos. | Miguel Ventura in Fafe, Portugal, captured this image on August 28, 2022, and wrote: “Every now and then the night sky offers us moments like this. We can see the Pleiades and the constellation Taurus with the planet Mars between these 2 … below near the horizon the imposing constellation Orion appears.” Thank you, Miguel! Can you see the expanded glow around one of the Sword stars? That’s M42, the Orion Nebula.

Science and the Orion Nebula

According to modern astronomers, the Orion Nebula is an enormous cloud of gas and dust, one of many in our Milky Way galaxy. It lies roughly 1,300 light-years from Earth.

At some 30 light-years in diameter, this great nebulous cocoon is giving birth to perhaps a thousand stars. A young open star cluster, whose stars were born together in the gas cloud and are still loosely bound by gravity, appears within the nebula. Some people refer to it as the Orion Nebula Star Cluster. In 2012, an international team of astronomers suggested this cluster in the Orion Nebula might have a black hole at its heart.

Through small telescopes you can see the four brightest stars in the Orion Nebula, known as the Trapezium. The light of the young, hot Trapezium stars illuminate the Orion Nebula. These stars are only a million or so years old, babies on the scale of star lifetimes.

But most of the stars in this emerging cluster are veiled behind the Orion Nebula itself, the great stellar nursery in Orion’s Sword.

The Orion Nebula’s position is Right Ascension: 5h 35m; Declination: 5 degrees 23′ south.

Bottom line: The Orion Nebula appears to the eye as a tiny, hazy spot. But it’s a vast stellar nursery, a place where new stars are forming.

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View at EarthSky Community Photos. | Randy Strauss in Papillion, Nebraska, captured this telescopic view of the Orion Nebula on March 4, 2024. Thank you, Randy! The Orion Nebula is one of the most familiar celestial objects, easily visible to the unaided eye below the 3 stars of Orion’s Belt. But it’s a vast stellar nursery, a place where new stars are forming.

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Orion the Hunter is the most noticeable of all constellations. The three stars of Orion’s Belt jump out at you as a short, straight row of medium-bright stars, midway between Orion’s two brightest stars, Betelgeuse and Rigel. Once you find the Belt stars, you can also locate the Orion Nebula, otherwise known as M42. When you look at it, you’re gazing toward a stellar nursery, a place where new stars are born.

How to locate the Orion Nebula

If you want to find this famous nebula, first you have to locate the constellation Orion. Fortunately, that’s easy, if you’re looking at the right time of year. The Northern Hemisphere winter months (Southern Hemisphere summer months) are the perfect time to come to know Orion.

First, look for the three medium-bright stars in a short, straight row. These stars represent Orion’s Belt.

Next, if you look closely, you’ll notice a curved line of stars “hanging” from the three Belt stars. These stars represent Orion’s Sword. Look for the Orion Nebula about midway down in the Sword of Orion.

As a general rule, the higher the constellation Orion is in the sky, the easier it is to see the Orion Nebula. From Northern Hemisphere locations, Orion is due south and highest in the sky around midnight in the middle of December. The stars return to the same place in the sky some four minutes earlier each night, or two hours earlier each month. So look for Orion to be highest up around 10 p.m. in mid-January and 8 p.m. in mid-February.

Another time people notice Orion is around the months of August and September, when this constellation appears in the east before dawn.

Orion the Hunter – visible to both hemispheres – rises in the east on December evenings. Chart via Chelynne Campion/ EarthSky.

A globe of luminescent fog

Most nebulae – clouds of interstellar gas and dust – are difficult if not impossible to see with the unaided eye or even binoculars. But the Orion Nebula is in a class nearly all by itself. It’s visible to the unaided eye on a dark, moonless night. To me, it looks like a star encased in a globe of luminescent fog. The star-gazing aficionado Stephen James O’Meara described it as:

… angel’s breath against a frosted sky.

In a dark-sky location, observe the Orion Nebula for yourself to see what it looks like. A backyard telescope, or even binoculars, will do wonders to showcase one of the greatest celestial treasures in the winter sky.

View at EarthSky Community Photos. | Miguel Ventura in Fafe, Portugal, captured this image on August 28, 2022, and wrote: “Every now and then the night sky offers us moments like this. We can see the Pleiades and the constellation Taurus with the planet Mars between these 2 … below near the horizon the imposing constellation Orion appears.” Thank you, Miguel! Can you see the expanded glow around one of the Sword stars? That’s M42, the Orion Nebula.

Science and the Orion Nebula

According to modern astronomers, the Orion Nebula is an enormous cloud of gas and dust, one of many in our Milky Way galaxy. It lies roughly 1,300 light-years from Earth.

At some 30 light-years in diameter, this great nebulous cocoon is giving birth to perhaps a thousand stars. A young open star cluster, whose stars were born together in the gas cloud and are still loosely bound by gravity, appears within the nebula. Some people refer to it as the Orion Nebula Star Cluster. In 2012, an international team of astronomers suggested this cluster in the Orion Nebula might have a black hole at its heart.

Through small telescopes you can see the four brightest stars in the Orion Nebula, known as the Trapezium. The light of the young, hot Trapezium stars illuminate the Orion Nebula. These stars are only a million or so years old, babies on the scale of star lifetimes.

But most of the stars in this emerging cluster are veiled behind the Orion Nebula itself, the great stellar nursery in Orion’s Sword.

The Orion Nebula’s position is Right Ascension: 5h 35m; Declination: 5 degrees 23′ south.

Bottom line: The Orion Nebula appears to the eye as a tiny, hazy spot. But it’s a vast stellar nursery, a place where new stars are forming.

Enjoying EarthSky? Sign up for our free daily newsletter today!

The post The Orion Nebula (M42) is a starry nursery first appeared on EarthSky.

from EarthSky https://ift.tt/OI1NuF5