Have skull drill, will travel

"Anthropological genetics is a huge and growing field," says Kendra Sirak. The Emory graduate student has developed a specialized technique for drilling into ancient skulls to remove DNA samples. (Photo by Kristin Stewardson.)

By Carol Clark

“Wherever I travel, I take my bone drill with me,” says Kendra Sirak.

An Emory PhD candidate in anthropology, Sirak has developed a specialized technique for drilling into ancient skulls to remove DNA samples. She’s flown to more than a dozen countries and drilled more than 1,000 skulls, perfecting the technique.

“No one at customs has ever questioned me about why I’m carrying a gigantic drill in my suitcase,” she notes.

Sirak has the distinction of being the last graduate student of the late George Armelagos, Goodrich C. White Professor of Anthropology. Armelagos, who died in 2014 at the age of 77, was one of the founders of the field of paleopathology.

He spent decades working with graduate students to study the bones of ancient Sudanese Nubians to learn about patterns of health, illness and death in the past. The only piece missing in studies of this population was genetic analysis. So in 2013, Armelagos sent Sirak to one of the best ancient DNA labs in the world, University College Dublin, with samples of the Nubian bones.

“I had no interest in genetics,” says Sirak, who was passionate about studying human bones and paleopathology. “But George believed DNA was going to become a critical part of anthropological research.”

Sirak drills the base of an ancient skull.

Sirak soon became hooked when she saw how she could combine her interest in ancient bones with insights from DNA. She formed collaborations not just in Dublin but at Harvard Medical School’s Department of Genetics and elsewhere, working on unsolved mysteries surrounding deaths going back anywhere from decades to ancient times.

As genetic sequencing techniques keep improving, anthropology and DNA analysis are becoming increasingly complementary. In 2015, another breakthrough occurred when researchers realized that the petrous bone consistently yielded the most DNA from ancient skeletons. This pyramid-shaped bone houses several parts of the inner ear related to hearing and balance.

But the way the petrous bone is wedged into the skull makes it difficult to access without shattering the cranium. Understandably, museum curators were reluctant to allow DNA researchers to tamper with rare, fragile ancient skulls.

So Sirak set about developing a technique to drill into a skull and reach the petrous bone in the most non-invasive way possible, while also getting enough bone powder for DNA analysis. The journal Biotechniques recently published her method, which involves drilling through the cranial base, where the spinal cord enters the skull.

“Hopefully, it will become the gold standard for both anthropology stewardship as well as DNA analysis,” Sirak says.

Sirak herself has the most experience in using the technique and her services have been in demand, as researchers seek to unlock secrets of ancient skeletons in museums and other collections.

Sirak’s trusty bone drill is a more modern version of the electric drill her father kept in the garage for household projects. Hers, however, has a foot pedal giving her precision control over the drill’s speed, and a flexible extension cord similar to what you might encounter in a dentist’s chair. The drill bits she uses range from 3.4 to 4.8 millimeters in diameter.

“Drilling an ancient skull can be nerve wracking,” Sirak says, “because you don’t want to be responsible for ruining a specimen. I’ve had museum curators watch me over my shoulder. Sometimes they are so close you can feel their breath on your neck.”

Besides drilling for DNA, she speaks at conferences, gives demonstrations and trains other researchers in her technique. “It’s a lot of fun to work with others who want to learn,” says Sirak, who has helped set up ancient DNA labs in India and China.

She is now finishing up her dissertation, a bioethnography of the ancient Nubians, and expects to graduate from Emory in June.

“Anthropological genetics is a huge and growing field,” Sirak says, acknowledging Armelagos for setting her on the path. “He was a good mentor. He introduced me to something that I didn’t know existed and let me run with it.”

Related:
Malawi yields oldest known DNA from Africa
Adding anthropology to genetics to study ancient DNA

from eScienceCommons http://ift.tt/2zNu6Bv

"Anthropological genetics is a huge and growing field," says Kendra Sirak. The Emory graduate student has developed a specialized technique for drilling into ancient skulls to remove DNA samples. (Photo by Kristin Stewardson.)

By Carol Clark

“Wherever I travel, I take my bone drill with me,” says Kendra Sirak.

An Emory PhD candidate in anthropology, Sirak has developed a specialized technique for drilling into ancient skulls to remove DNA samples. She’s flown to more than a dozen countries and drilled more than 1,000 skulls, perfecting the technique.

“No one at customs has ever questioned me about why I’m carrying a gigantic drill in my suitcase,” she notes.

Sirak has the distinction of being the last graduate student of the late George Armelagos, Goodrich C. White Professor of Anthropology. Armelagos, who died in 2014 at the age of 77, was one of the founders of the field of paleopathology.

He spent decades working with graduate students to study the bones of ancient Sudanese Nubians to learn about patterns of health, illness and death in the past. The only piece missing in studies of this population was genetic analysis. So in 2013, Armelagos sent Sirak to one of the best ancient DNA labs in the world, University College Dublin, with samples of the Nubian bones.

“I had no interest in genetics,” says Sirak, who was passionate about studying human bones and paleopathology. “But George believed DNA was going to become a critical part of anthropological research.”

Sirak drills the base of an ancient skull.

Sirak soon became hooked when she saw how she could combine her interest in ancient bones with insights from DNA. She formed collaborations not just in Dublin but at Harvard Medical School’s Department of Genetics and elsewhere, working on unsolved mysteries surrounding deaths going back anywhere from decades to ancient times.

As genetic sequencing techniques keep improving, anthropology and DNA analysis are becoming increasingly complementary. In 2015, another breakthrough occurred when researchers realized that the petrous bone consistently yielded the most DNA from ancient skeletons. This pyramid-shaped bone houses several parts of the inner ear related to hearing and balance.

But the way the petrous bone is wedged into the skull makes it difficult to access without shattering the cranium. Understandably, museum curators were reluctant to allow DNA researchers to tamper with rare, fragile ancient skulls.

So Sirak set about developing a technique to drill into a skull and reach the petrous bone in the most non-invasive way possible, while also getting enough bone powder for DNA analysis. The journal Biotechniques recently published her method, which involves drilling through the cranial base, where the spinal cord enters the skull.

“Hopefully, it will become the gold standard for both anthropology stewardship as well as DNA analysis,” Sirak says.

Sirak herself has the most experience in using the technique and her services have been in demand, as researchers seek to unlock secrets of ancient skeletons in museums and other collections.

Sirak’s trusty bone drill is a more modern version of the electric drill her father kept in the garage for household projects. Hers, however, has a foot pedal giving her precision control over the drill’s speed, and a flexible extension cord similar to what you might encounter in a dentist’s chair. The drill bits she uses range from 3.4 to 4.8 millimeters in diameter.

“Drilling an ancient skull can be nerve wracking,” Sirak says, “because you don’t want to be responsible for ruining a specimen. I’ve had museum curators watch me over my shoulder. Sometimes they are so close you can feel their breath on your neck.”

Besides drilling for DNA, she speaks at conferences, gives demonstrations and trains other researchers in her technique. “It’s a lot of fun to work with others who want to learn,” says Sirak, who has helped set up ancient DNA labs in India and China.

She is now finishing up her dissertation, a bioethnography of the ancient Nubians, and expects to graduate from Emory in June.

“Anthropological genetics is a huge and growing field,” Sirak says, acknowledging Armelagos for setting her on the path. “He was a good mentor. He introduced me to something that I didn’t know existed and let me run with it.”

Related:
Malawi yields oldest known DNA from Africa
Adding anthropology to genetics to study ancient DNA

from eScienceCommons http://ift.tt/2zNu6Bv

Most blue whales are ‘right-handed’

This aerial photo shows a blue whale lunge as it feeds near the ocean surface. New research shows blue whales show a right-side preference for rolling behavior during feeding, but they roll to the left side for more acrobatic feeding behaviors. Photograph courtesy of John Durban (NOAA) and Michael Moore (WHOI)/ via UC Santa Cruz.

A wonderful recent study describes the intricacies of the feeding behavior of the blue whale, the largest animal on Earth, perhaps the largest animal ever to have lived on Earth. While feeding, a blue whale accelerates underwater and opens its mouth to take in great quantities of seawater. The mighty whale then traps its prey – tiny creatures called krill – by forcing the water through sieve-like plates in its mouth, called baleen plates. All of this is known, but what wasn’t known was that most blue whales appear to have a right-side lateralization bias – that is, they roll to the right most often – as they feed. That’s the case except, as it turns out, when they swim upward from the ocean depths.

Cetacean expert Ari Friedlaender of the Marine Mammal Institute at Oregon State University and UC Santa Cruz led the study. It was published November 20, 2017 in the peer-reviewed journal Current Biology.

Friedlaender’s team used motion-sensing tags to track the movements of more than five dozen blue whales off the California coast. They collected data on more than 2,800 rolling lunges for prey by the 63 different whales. Friedlaender commented in a statement:

Most of the movements we tracked that involved ‘handedness’ – perhaps as much as 90 percent – involved 90-degree side rolls, which is how they feed most of the time. Blue whales approach a patch of krill and turn on their sides. We found many of them exclusively rolled to their right, fewer rolled just to their left, and the rest exhibited a combination.

This had never been documented in blue whales before …

The statement explained that this result “didn’t necessarily surprise the researchers” because many animals have a right-side bias, and for good reason:

In vertebrates, the left hemisphere of the brain controls coordination, predictive motor control and the ability to plan and coordinate actions – like feeding. And the left side of the brain is linked with the right eye.

Blue whale feeding on krill. Image via Monterey Bay Aquarium.

A swarm of krill, via NOAA/ Wikimedia Commons.

What did surprise them was that even “right-handed” whales become left-handed when it comes to one move. When blue whales rise from the depths to approach krill near the surface, they perform 360-degree barrel rolls at a steep angle and nearly always roll to the left. Friedlaender said:

The patches of prey near the surface, between 10 and 100 feet deep, are usually smaller and less dense than prey patches found deeper and the blue whales showed a bias toward rolling left – presumably so they can keep their right eye on the prey patch and maximize their effort.

These are the largest animals on the planet and feeding is an extraordinarily costly behavior that takes time, so being able to maximize the benefit of each feeding opportunity is critical. And we believe this left-sided rotation is a mechanism to help achieve that.

That left lateralization bias is unusual in the animal kingdom, the researchers noted.

And, in case you’re wondering, the video below shows what it’s like to tag a whale!

Bottom line: A team of scientists has used motion-sensing tags to show that most blue whales do have a right-side lateralization bias – except when they swim upward.

Via Oregon State University and UC Santa Cruz.

Source: Context-dependent lateralized feeding strategies in blue whales

from EarthSky http://ift.tt/2Ad5YY4

This aerial photo shows a blue whale lunge as it feeds near the ocean surface. New research shows blue whales show a right-side preference for rolling behavior during feeding, but they roll to the left side for more acrobatic feeding behaviors. Photograph courtesy of John Durban (NOAA) and Michael Moore (WHOI)/ via UC Santa Cruz.

A wonderful recent study describes the intricacies of the feeding behavior of the blue whale, the largest animal on Earth, perhaps the largest animal ever to have lived on Earth. While feeding, a blue whale accelerates underwater and opens its mouth to take in great quantities of seawater. The mighty whale then traps its prey – tiny creatures called krill – by forcing the water through sieve-like plates in its mouth, called baleen plates. All of this is known, but what wasn’t known was that most blue whales appear to have a right-side lateralization bias – that is, they roll to the right most often – as they feed. That’s the case except, as it turns out, when they swim upward from the ocean depths.

Cetacean expert Ari Friedlaender of the Marine Mammal Institute at Oregon State University and UC Santa Cruz led the study. It was published November 20, 2017 in the peer-reviewed journal Current Biology.

Friedlaender’s team used motion-sensing tags to track the movements of more than five dozen blue whales off the California coast. They collected data on more than 2,800 rolling lunges for prey by the 63 different whales. Friedlaender commented in a statement:

Most of the movements we tracked that involved ‘handedness’ – perhaps as much as 90 percent – involved 90-degree side rolls, which is how they feed most of the time. Blue whales approach a patch of krill and turn on their sides. We found many of them exclusively rolled to their right, fewer rolled just to their left, and the rest exhibited a combination.

This had never been documented in blue whales before …

The statement explained that this result “didn’t necessarily surprise the researchers” because many animals have a right-side bias, and for good reason:

In vertebrates, the left hemisphere of the brain controls coordination, predictive motor control and the ability to plan and coordinate actions – like feeding. And the left side of the brain is linked with the right eye.

Blue whale feeding on krill. Image via Monterey Bay Aquarium.

A swarm of krill, via NOAA/ Wikimedia Commons.

What did surprise them was that even “right-handed” whales become left-handed when it comes to one move. When blue whales rise from the depths to approach krill near the surface, they perform 360-degree barrel rolls at a steep angle and nearly always roll to the left. Friedlaender said:

The patches of prey near the surface, between 10 and 100 feet deep, are usually smaller and less dense than prey patches found deeper and the blue whales showed a bias toward rolling left – presumably so they can keep their right eye on the prey patch and maximize their effort.

These are the largest animals on the planet and feeding is an extraordinarily costly behavior that takes time, so being able to maximize the benefit of each feeding opportunity is critical. And we believe this left-sided rotation is a mechanism to help achieve that.

That left lateralization bias is unusual in the animal kingdom, the researchers noted.

And, in case you’re wondering, the video below shows what it’s like to tag a whale!

Bottom line: A team of scientists has used motion-sensing tags to show that most blue whales do have a right-side lateralization bias – except when they swim upward.

Via Oregon State University and UC Santa Cruz.

Source: Context-dependent lateralized feeding strategies in blue whales

from EarthSky http://ift.tt/2Ad5YY4

Early morning halo over Idaho

Photo taken November 25, 2017 by Sheryl R. Garrison. Visit her website.

from EarthSky http://ift.tt/2zxm2AU

Photo taken November 25, 2017 by Sheryl R. Garrison. Visit her website.

from EarthSky http://ift.tt/2zxm2AU

Saturn-Mercury conjunction is 1st of 3

On November 28, 2017, the innermost planet Mercury will swing 3^o south of the 6th planet, Saturn, on our sky’s dome. Astronomers call this event – when two planets lie north and south of one another on the sky’s dome – a conjunction. The conjunction of Mercury and Saturn on November 28 is the first in a series of three Mercury-Saturn conjunctions … that is, the first part of what astronomers call a triple conjunction. More about that below.

First, here’s the view on November 28. Mercury and Saturn are both low in the west after sunset. Find an unobstructed horizon in the direction of sunset, and, if possible, perch yourself on a hill or balcony. Then look for Mercury and Saturn low in the western sky, near the sunset point on the horizon, as soon as the sky begins to darken.

Mercury is the brighter of these two starlike objects, shining almost twice as brightly as Saturn. So if you only see one point of light, it’s probably Mercury. Three degrees of sky approximates the width of your thumb at an arm’s length from your eye. On and around November 28, both of these worlds will fit inside the same binocular field of view.

The Southern Hemisphere has the advantage over the Northern Hemisphere for seeing Mercury and Saturn. South of the equator, these two worlds stay out for one and one-half hours (or more) after sunset. At mid-northern latitudes, the twosome doesn’t stay out for a lot longer than one hour after the sun.

Click here for recommended almanacs; they can help you find out the setting times for Mercury and Saturn in your sky

From the Northern Hemisphere, Mercury sets first and then Saturn sets afterwards. South of the equator, Saturn sets first and then Mercury plunges beneath the horizon. As one might expect, Mercury and Saturn set at nearly the same time at the equator.

The conjunction of Mercury and Saturn on November 28 is the first in a series of three Mercury-Saturn conjunctions. The term triple conjunction is used whenever two planets, or a planet and a star, appear due north-south of each other in the sky three different times in a relatively short space of a few months. That’s what’s happening here.

The second conjunction occurs on December 6, 2017, when Mercury swings less than 1.5^o south of Saturn. But this conjunction will be very hard to catch because – by that time – both Mercury and Saturn will be buried deeply in in the glare of sunset.

The third conjunction of this triple conjunction will the closest of them all, with Mercury sweeping about 0.7^o south of Saturn on January 13, 2018. (Seven-tenths of one degree on the sky’s dome is approximately equal to the width of your little finger at an arm’s length.) This conjunction on January 13, 2018, which occurs in the morning sky, should be fairly easy to view – especially since the lit side of the waning crescent moon will be pointing right at Mercury and Saturn.

The morning conjunction on January 13, 2018, concludes the upcoming triple conjunction of Mercury and Saturn. The first one takes place in the evening sky on November 28, 2017.

In the meantime, though, see if you can catch the evening conjunction of Mercury and Saturn after sunset on November 28, 2017.

from EarthSky http://ift.tt/2zTIsfi

On November 28, 2017, the innermost planet Mercury will swing 3^o south of the 6th planet, Saturn, on our sky’s dome. Astronomers call this event – when two planets lie north and south of one another on the sky’s dome – a conjunction. The conjunction of Mercury and Saturn on November 28 is the first in a series of three Mercury-Saturn conjunctions … that is, the first part of what astronomers call a triple conjunction. More about that below.

First, here’s the view on November 28. Mercury and Saturn are both low in the west after sunset. Find an unobstructed horizon in the direction of sunset, and, if possible, perch yourself on a hill or balcony. Then look for Mercury and Saturn low in the western sky, near the sunset point on the horizon, as soon as the sky begins to darken.

Mercury is the brighter of these two starlike objects, shining almost twice as brightly as Saturn. So if you only see one point of light, it’s probably Mercury. Three degrees of sky approximates the width of your thumb at an arm’s length from your eye. On and around November 28, both of these worlds will fit inside the same binocular field of view.

The Southern Hemisphere has the advantage over the Northern Hemisphere for seeing Mercury and Saturn. South of the equator, these two worlds stay out for one and one-half hours (or more) after sunset. At mid-northern latitudes, the twosome doesn’t stay out for a lot longer than one hour after the sun.

Click here for recommended almanacs; they can help you find out the setting times for Mercury and Saturn in your sky

From the Northern Hemisphere, Mercury sets first and then Saturn sets afterwards. South of the equator, Saturn sets first and then Mercury plunges beneath the horizon. As one might expect, Mercury and Saturn set at nearly the same time at the equator.

The conjunction of Mercury and Saturn on November 28 is the first in a series of three Mercury-Saturn conjunctions. The term triple conjunction is used whenever two planets, or a planet and a star, appear due north-south of each other in the sky three different times in a relatively short space of a few months. That’s what’s happening here.

The second conjunction occurs on December 6, 2017, when Mercury swings less than 1.5^o south of Saturn. But this conjunction will be very hard to catch because – by that time – both Mercury and Saturn will be buried deeply in in the glare of sunset.

The third conjunction of this triple conjunction will the closest of them all, with Mercury sweeping about 0.7^o south of Saturn on January 13, 2018. (Seven-tenths of one degree on the sky’s dome is approximately equal to the width of your little finger at an arm’s length.) This conjunction on January 13, 2018, which occurs in the morning sky, should be fairly easy to view – especially since the lit side of the waning crescent moon will be pointing right at Mercury and Saturn.

The morning conjunction on January 13, 2018, concludes the upcoming triple conjunction of Mercury and Saturn. The first one takes place in the evening sky on November 28, 2017.

In the meantime, though, see if you can catch the evening conjunction of Mercury and Saturn after sunset on November 28, 2017.

from EarthSky http://ift.tt/2zTIsfi

When is my earliest sunset?

Adrian Strand captured this photo on a beach in northwest England.

The winter solstice is the shortest day. It offers the shortest period of daylight. But, unless you live close to the Arctic Circle or Antarctic Circle, your earliest sunsets aren’t on or even near the solstice itself. Instead, your earliest sunsets will come before the winter solstice. The exact date of earliest sunset depends on your latitude. If you live in the southernmost U.S., or a comparable latitude (say, around 25 or 26 degrees N. latitude), your earliest sunsets are in late November. If you’re farther north – say, around 40 degrees N. latitude – your earliest sunsets are in early to mid-December.

And if you live in the Southern Hemisphere, your earliest sunrises are coming around now. Southern Hemisphere? Click here.

Why isn’t the earliest sunset on the year’s shortest day? To understand it, try thinking about it in terms of solar noon or midday, the time midway between sunrise and sunset, when the sun reaches its highest point for the day.

A clock ticks off exactly 24 hours from one noon to the next. But the actual days – as measured by the spin of the Earth – are rarely exactly 24 hours long.

So the exact time of solar noon, as measured by Earth’s spin, shifts in a seasonal way. If you measured Earth’s spin from one solar noon to the next, you’d find that – around the time of the December solstice – the time period between consecutive solar noons is actually half a minute longer than 24 hours.

So – two weeks before the solstice, for example – the sun reaches its noontime position at 11:52 a.m. local standard time. Two weeks later – on the winter solstice – the sun reaches its noontime position at 11:59 a.m. That’s 7 minutes later.

The later clock time for solar noon also means a later clock time for sunrise and sunset.

The result: earlier sunsets before the winter solstice and increasingly later sunrises for a few weeks after the winter solstice.

The exact date of earliest sunset varies with latitude. But the sequence is always the same. For the Northern Hemisphere, earliest sunset in early December, winter solstice, latest sunrise in early January.

In early December, the Southern Hemisphere is approaching its summer solstice. Sunset on that part of Earth will continue coming later until early July. Photo of sunset with crepuscular rays by Phil Rettke Photography in Ipswich, Queensland, Australia.

Meanwhile, if you’re in the Southern Hemisphere, take nearly everything we say here and apply it to your winter solstice in June. For the Southern Hemisphere, the earliest sunsets come prior to the winter solstice, which is typically around June 21. The latest sunrises occur after the June winter solstice.

During the month of December, it’s nearly summer in the Southern Hemisphere; the summer solstice comes this month for that hemisphere. So sunsets and sunrises are shifting in a similar way. For both hemispheres, the sequence in summer is: earliest sunrises before the summer solstice, then the summer solstice itself, then latest sunsets after the summer solstice.

As always, things get tricky if you look closely. Assuming you’re at a mid-temperate latitude, the earliest sunset for the Northern Hemisphere – and earliest sunrise for the Southern Hemisphere – come about two weeks before the December solstice, and the latest sunrise/latest sunset happen about two weeks after.

But at the other end of the year, in June and July, the time period is not equivalent. Again assuming a mid-temperate latitude, the earliest sunrise for the Northern Hemisphere – and earliest sunset for the Southern Hemisphere – comes only about one week before the June solstice, and the latest sunset/latest sunrise happens about one week after.

The time difference is due to the fact that the December solstice occurs when Earth is near its perihelion – or closest point to the sun – around which time we’re moving fastest in orbit. Meanwhile, the June solstice occurs when Earth is near aphelion – our farthest point from the sun – around which time we’re moving at our slowest in orbit.

View larger. Computed position of the sun looking eastward at the same time each morning from the Northern Hemisphere. December solstice point at lower right and June solstice point at upper left. Solar days are longer than 24 hours long at the solstices, yet less than 24 hours long at the equinoxes. Roughly midway between a solstice and an equinox, or vice versa, the solar day is exactly 24 hours long.

In short, the earliest sunset/winter solstice/latest sunrise and earliest sunrise/summer solstice/latest sunset phenomena are due to the fact that true solar days are longer than 24 hours long for several weeks before and after the solstices. At and around the solstices, the Earth must rotate farther on its axis for the sun to return to its daily noontime position, primarily because the sun is appreciably north or south of the Earth’s equator.

However, perihelion accentuates the effect around the December solstice, giving a day length of 24 hours 30 seconds. And aphelion lessens the effect around the June solstice, giving a day length of 24 hours 13 seconds.

Bottom line: The earliest sunsets and latest sunrises don’t come on the winter solstice, the shortest day of the year. Instead, earliest sunsets come some weeks before the winter solstice. Latest sunrises come some weeks after it.

Here are more details about the earliest sunsets.

from EarthSky http://ift.tt/1tNt1eN

Adrian Strand captured this photo on a beach in northwest England.

The winter solstice is the shortest day. It offers the shortest period of daylight. But, unless you live close to the Arctic Circle or Antarctic Circle, your earliest sunsets aren’t on or even near the solstice itself. Instead, your earliest sunsets will come before the winter solstice. The exact date of earliest sunset depends on your latitude. If you live in the southernmost U.S., or a comparable latitude (say, around 25 or 26 degrees N. latitude), your earliest sunsets are in late November. If you’re farther north – say, around 40 degrees N. latitude – your earliest sunsets are in early to mid-December.

And if you live in the Southern Hemisphere, your earliest sunrises are coming around now. Southern Hemisphere? Click here.

Why isn’t the earliest sunset on the year’s shortest day? To understand it, try thinking about it in terms of solar noon or midday, the time midway between sunrise and sunset, when the sun reaches its highest point for the day.

A clock ticks off exactly 24 hours from one noon to the next. But the actual days – as measured by the spin of the Earth – are rarely exactly 24 hours long.

So the exact time of solar noon, as measured by Earth’s spin, shifts in a seasonal way. If you measured Earth’s spin from one solar noon to the next, you’d find that – around the time of the December solstice – the time period between consecutive solar noons is actually half a minute longer than 24 hours.

So – two weeks before the solstice, for example – the sun reaches its noontime position at 11:52 a.m. local standard time. Two weeks later – on the winter solstice – the sun reaches its noontime position at 11:59 a.m. That’s 7 minutes later.

The later clock time for solar noon also means a later clock time for sunrise and sunset.

The result: earlier sunsets before the winter solstice and increasingly later sunrises for a few weeks after the winter solstice.

The exact date of earliest sunset varies with latitude. But the sequence is always the same. For the Northern Hemisphere, earliest sunset in early December, winter solstice, latest sunrise in early January.

In early December, the Southern Hemisphere is approaching its summer solstice. Sunset on that part of Earth will continue coming later until early July. Photo of sunset with crepuscular rays by Phil Rettke Photography in Ipswich, Queensland, Australia.

Meanwhile, if you’re in the Southern Hemisphere, take nearly everything we say here and apply it to your winter solstice in June. For the Southern Hemisphere, the earliest sunsets come prior to the winter solstice, which is typically around June 21. The latest sunrises occur after the June winter solstice.

During the month of December, it’s nearly summer in the Southern Hemisphere; the summer solstice comes this month for that hemisphere. So sunsets and sunrises are shifting in a similar way. For both hemispheres, the sequence in summer is: earliest sunrises before the summer solstice, then the summer solstice itself, then latest sunsets after the summer solstice.

As always, things get tricky if you look closely. Assuming you’re at a mid-temperate latitude, the earliest sunset for the Northern Hemisphere – and earliest sunrise for the Southern Hemisphere – come about two weeks before the December solstice, and the latest sunrise/latest sunset happen about two weeks after.

But at the other end of the year, in June and July, the time period is not equivalent. Again assuming a mid-temperate latitude, the earliest sunrise for the Northern Hemisphere – and earliest sunset for the Southern Hemisphere – comes only about one week before the June solstice, and the latest sunset/latest sunrise happens about one week after.

The time difference is due to the fact that the December solstice occurs when Earth is near its perihelion – or closest point to the sun – around which time we’re moving fastest in orbit. Meanwhile, the June solstice occurs when Earth is near aphelion – our farthest point from the sun – around which time we’re moving at our slowest in orbit.

View larger. Computed position of the sun looking eastward at the same time each morning from the Northern Hemisphere. December solstice point at lower right and June solstice point at upper left. Solar days are longer than 24 hours long at the solstices, yet less than 24 hours long at the equinoxes. Roughly midway between a solstice and an equinox, or vice versa, the solar day is exactly 24 hours long.

In short, the earliest sunset/winter solstice/latest sunrise and earliest sunrise/summer solstice/latest sunset phenomena are due to the fact that true solar days are longer than 24 hours long for several weeks before and after the solstices. At and around the solstices, the Earth must rotate farther on its axis for the sun to return to its daily noontime position, primarily because the sun is appreciably north or south of the Earth’s equator.

However, perihelion accentuates the effect around the December solstice, giving a day length of 24 hours 30 seconds. And aphelion lessens the effect around the June solstice, giving a day length of 24 hours 13 seconds.

Bottom line: The earliest sunsets and latest sunrises don’t come on the winter solstice, the shortest day of the year. Instead, earliest sunsets come some weeks before the winter solstice. Latest sunrises come some weeks after it.

Here are more details about the earliest sunsets.

from EarthSky http://ift.tt/1tNt1eN

Now we know Earth blocks neutrinos

A visual representation of one of the highest-energy neutrino detections, superimposed on a view of the IceCube Lab near Earth’s South Pole. Image via IceCube Collaboration/ Penn State.

It used to be said that neutrinos were massless and would pass through anything. But in recent years, scientists have realized that these strange particles – some of which were formed in the first second of the early universe, and which travel at the speed of light – are only practically massless. And now it’s been proven experimentally, by scientists working with data at the IceCube detector at Earth’s South Pole, that very energetic neutrinos can, in fact, be blocked. Doug Cowen at Penn State University was a collaborator on the study. He said:

This achievement is important because it shows, for the first time, that very-high-energy neutrinos can be absorbed by something — in this case, the Earth.

The results of this recent experiment were published in the online edition of the peer-reviewed journal Nature on November 22, 2017.

At the highest energies, neutrinos will be absorbed by Earth and will never make it to IceCube. Image via IceCube Collaboration.

The IceCube detector is an array of 5,160 basketball-sized sensors frozen deep within a cubic kilometer of very clear ice near the South Pole. The detector made the first detections of extremely-high-energy neutrinos in 2013, but a mystery remained about whether any kind of matter could truly stop a neutrino’s journey through space. Cowen said:

We knew that lower-energy neutrinos pass through just about anything, but although we had expected higher-energy neutrinos to be different, no previous experiments had been able to demonstrate convincingly that higher-energy neutrinos could be stopped by anything.

A statement from these scientists said:

The study … is based on one year of data from about 10,800 neutrino-related interactions, stemming from a natural supply of very energetic neutrinos from space that go through a thick and dense absorber: the Earth. The energy of the neutrinos was critical to the study, as higher energy neutrinos are more likely to interact with matter and be absorbed by the Earth.

Scientists found that there were fewer energetic neutrinos making it all the way through the Earth to the IceCube detector than from less obstructed paths, such as those coming in at near-horizontal trajectories.

The probability of neutrinos being absorbed by the Earth was consistent with expectations from the Standard Model of particle physics, which scientists use to explain the fundamental forces and particles in the universe.

Read more from the IceCube Collaboration.

The Standard Model predicts that the probability that a neutrino interacts with matter increases with energy. Thus the recent results from IceCube agrees with the Standard Model, for energies up to 980 TeV. New physics could show up as deviations to this prediction at higher energies. Image via IceCube Collaboration.

Bottom line: It used to be said that neutrinos would “pass through anything.” An experiment near the South Pole reveals how Earth blocks them.

Source: Measurement of the multi-TeV neutrino interaction cross-section with IceCube using Earth absorption

from EarthSky http://ift.tt/2iWor1u

A visual representation of one of the highest-energy neutrino detections, superimposed on a view of the IceCube Lab near Earth’s South Pole. Image via IceCube Collaboration/ Penn State.

It used to be said that neutrinos were massless and would pass through anything. But in recent years, scientists have realized that these strange particles – some of which were formed in the first second of the early universe, and which travel at the speed of light – are only practically massless. And now it’s been proven experimentally, by scientists working with data at the IceCube detector at Earth’s South Pole, that very energetic neutrinos can, in fact, be blocked. Doug Cowen at Penn State University was a collaborator on the study. He said:

This achievement is important because it shows, for the first time, that very-high-energy neutrinos can be absorbed by something — in this case, the Earth.

The results of this recent experiment were published in the online edition of the peer-reviewed journal Nature on November 22, 2017.

At the highest energies, neutrinos will be absorbed by Earth and will never make it to IceCube. Image via IceCube Collaboration.

The IceCube detector is an array of 5,160 basketball-sized sensors frozen deep within a cubic kilometer of very clear ice near the South Pole. The detector made the first detections of extremely-high-energy neutrinos in 2013, but a mystery remained about whether any kind of matter could truly stop a neutrino’s journey through space. Cowen said:

We knew that lower-energy neutrinos pass through just about anything, but although we had expected higher-energy neutrinos to be different, no previous experiments had been able to demonstrate convincingly that higher-energy neutrinos could be stopped by anything.

A statement from these scientists said:

The study … is based on one year of data from about 10,800 neutrino-related interactions, stemming from a natural supply of very energetic neutrinos from space that go through a thick and dense absorber: the Earth. The energy of the neutrinos was critical to the study, as higher energy neutrinos are more likely to interact with matter and be absorbed by the Earth.

Scientists found that there were fewer energetic neutrinos making it all the way through the Earth to the IceCube detector than from less obstructed paths, such as those coming in at near-horizontal trajectories.

The probability of neutrinos being absorbed by the Earth was consistent with expectations from the Standard Model of particle physics, which scientists use to explain the fundamental forces and particles in the universe.

Read more from the IceCube Collaboration.

The Standard Model predicts that the probability that a neutrino interacts with matter increases with energy. Thus the recent results from IceCube agrees with the Standard Model, for energies up to 980 TeV. New physics could show up as deviations to this prediction at higher energies. Image via IceCube Collaboration.

Bottom line: It used to be said that neutrinos would “pass through anything.” An experiment near the South Pole reveals how Earth blocks them.

Source: Measurement of the multi-TeV neutrino interaction cross-section with IceCube using Earth absorption

from EarthSky http://ift.tt/2iWor1u

Before you toss another thing in the trash, watch this video

Every day, the average American throws away about 4.4 pounds of waste, about the weight of one chihuahua. Multiple that by every day of the year and over 300 million Americans and you get 167,000,000 tons of trash a year — or the equivalent of 76 billion chihuahuas.

Meggie Stewart, a senior majoring in Environmental Sciences, did the math for her two-minute video about landfills (above) — the first place winner for the Emory Office of Sustainability Initiatives 2017 Waste Video Competition. Emory is striving to achieve zero landfill waste on campus, since landfills have negative social, economic and environmental impacts.

from eScienceCommons http://ift.tt/2A8DL4J

Every day, the average American throws away about 4.4 pounds of waste, about the weight of one chihuahua. Multiple that by every day of the year and over 300 million Americans and you get 167,000,000 tons of trash a year — or the equivalent of 76 billion chihuahuas.

Meggie Stewart, a senior majoring in Environmental Sciences, did the math for her two-minute video about landfills (above) — the first place winner for the Emory Office of Sustainability Initiatives 2017 Waste Video Competition. Emory is striving to achieve zero landfill waste on campus, since landfills have negative social, economic and environmental impacts.

from eScienceCommons http://ift.tt/2A8DL4J