Astronomers spy the Geminid meteors’ dust trail in space

View larger. | Look closely along the line of white dots. A faint dust trail is visible in places where the dots are omitted. This faint dust trail – left behind by 3200 Phaethon, parent body for the Geminid meteor shower – was captured for the first time by a camera called WISPR aboard the Parker Solar Probe. Image via Brendan Gallagher/ Guillermo Stenborg/ U.S. Naval Research Lab.

The 2019 Geminid meteor shower is happening now, and it peaks this weekend. Best morning is likely December 14, but try December 15, too; both mornings will feature a bright moon. As you may know, meteors in annual showers like the Geminids are the result of Earth’s encounter with trails of dust in space – called meteoroid streams by astronomers – left behind mainly by comets. The dust enters our atmosphere and vaporizes, producing the streaks of light we see as meteors or “shooting stars.” This week (December 11, 2019), astronomers at the U.S. Naval Research Laboratory held a press conference to discuss an actual image of a dust trail (above) left behind in space by the asteroid that spawned the Geminid meteor shower. It’s none other than mysterious 3200 Phaethon, an object of great interest and speculation.

Karl Battams – who goes by @SungrazerComets on Twitter – is a computational scientist the Naval Research Lab’s Space Science Division. At a NASA press conference on December 11, 2019, he discussed the new image, which comes from a Lab-built camera called WISPR. He said that 3200 Phaethon’s dust trail is best seen near the sun, where it’s most densely packed. And he said the data captured by WISPR determined the asteroid dust trail weighs an estimated billion tons, and measures more than 14 million miles (23 million km) long. He also said the findings raise questions about the trail’s origin:

Something catastrophic happened to Phaethon a couple of thousand years ago and created the Geminid meteor shower. There’s no way the asteroid is anywhere near active enough when it is near the sun to produce the mass of dust we are seeing …

Read more: NRL-camera aboard NASA spacecraft confirms asteroid phenomenon

And therein lies the essential mystery of 3200 Phaethon. Most meteor showers are spawned by comets. 3200 Phaethon is an asteroid. Comets are fragile, icy bodies that litter their orbits with debris. It’s easy to see how debris from a comet’s orbit can create a shower of meteors in Earth’s sky.

But a rocky asteroid? That’s tougher to understand.

Keep reading to learn more about mysterious 3200 Phaethon.

EarthSky lunar calendars are cool! They make great gifts. Order now. Going fast!

we were excited to see them from space as well!https://t.co/ejvkzcDpkK

— U.S. Naval Research Laboratory (@USNRL) December 11, 2019

3200 Phaethon is an odd color for an asteroid. Most asteroids are dull grey to red, depending on the type of material on their surface. 3200 Phaethon is blue. Blue asteroids are known, but make up only a fraction of all known asteroids. And Phaethon isn’t just blue. It’s one of the bluest of similarly-colored asteroids (or comets) in the solar system.

Here’s another odd feature of 3200 Phaethon. While comets tend to have more elliptical orbits, asteroid orbits are more circular. 3200 Phaethon’s orbit – which is now exceedingly well known – is highly elongated, reminiscent of some comets. Its orbit crosses the orbits of Mars, Earth, Venus and Mercury.

Orbital path of 3200 Phaethon, via SkyandTelescope.com. In 2017, 3200 Phaethon came closer to Earth than it will again until 2093. The Geminids are always a reliable shower, but the shower was extra special in 2017 because its parent object was nearby.

Plus its orbit brings 3200 Phaethon closer to the sun than any other named asteroid (though some smaller, unnamed asteroids come even closer). At its closest point, Phaethon is only 13 million miles (20.9 million km) from the sun. That’s less than half of Mercury’s closest distance. Its name honors this object’s relationship to the sun. In Greek mythology, Phaethon was the son of the sun god Helios.

3200 Phaethon’s orbit carries it so close to the sun that its surface heats up to about 1,500 degrees Fahrenheit (800 degrees C). That’s hot enough to melt aluminum.

It’s when it’s closest to the sun that 3200 Phaethon releases a tiny dust tail; that’s right, it’s a dust tail for an asteroid, one of only two known so far in our solar system. Scientists have said it’s possible the sun’s heat causes fractures, in much the same way a dry riverbed cracks in the afternoon heat.

Comets are known for their tails. 3200 Phaethon’s dust tail is one of the features of this object that blurs the line traditionally thought to set comets and asteroids apart.

This closeup image of 3200 Phaethon by NASA’s STEREO A spacecraft in 2017 shows a tail extending faintly toward lower left. Image via NASA/SkyandTelescope.com.

3200 Phaethon was the first asteroid to be discovered via spacecraft on October 11, 1983. Astronomers Simon F. Green and John K. Davies noticed it while searching Infrared Astronomical Satellite data for moving objects. Charles T. Kowal confirmed it optically and said it was asteroid-like in appearance. The object received the provisional designation 1983 TB. Two years later, in 1985, using the convention for naming asteroids, astronomers assigned it its asteroid number and name: 3200 Phaethon.

Before 3200 Phaethon, scientists linked all known meteor showers to active comets and not asteroids.

Thus 3200 Phaethon surprised them from the beginning, because – while it looked like an asteroid – it appeared to be the source of the annual Geminid meteor shower. Astronomers began calling 3200 Phaethon a comet-asteroid hybrid, an asteroid that behaves like a comet. Later, they began using the term rock-comet.

Radar images of 3200 Phaethon generated by astronomers at the Arecibo Observatory on December 17, 2017. Image via Wikipedia.

Astronomer Teddy Kareta of the University of Arizona’s Lunar and Planetary Laboratory has studied 3200 Phaethon. He commented in 2018:

[At first], the assumption was that Phaethon probably was a dead, burnt-out comet, but comets are typically red in color, and not blue. So, even though Phaethon’s highly eccentric orbit should scream ‘dead comet,’ it’s hard to say whether Phaethon is more like an asteroid or more like a dead comet.

The composition of 3200 Phaethon resembles that of asteroid 2 Pallas. Both are dark, B-type asteroids composed of materials that have been modified by water. The 1st in this series of Hubble images of 3200 Phaethon in 2017 is marked with the asteroid’s spin axis (top) and south pole. Image via B. E. Schmidt et. al/NASA/ESA/SkyandTelescope.com.

3200 Phaethon is classified as a potentially hazardous asteroid, which doesn’t mean it’s a threat to Earth. It just means two things. First, 3200 Phaethon is big – about 3 miles (5 km) wide – big enough to cause significant regional damage if it were to strike Earth.

Second, it’s known to make periodic close approaches to Earth.

The 2017 “close approach” brought this object to about 26 times the moon’s distance. Astronomers know of no upcoming strike by this object in this foreseeable future.

Both amateur and professional astronomers watched 3200 Phaethon as carefully as they could in 2017. For example, Northolt Branch Observatories in London, England, created the animation below from images it captured in 2017.

Steven Bellavia also produced a video of 3200 Phaethon in 2017 – below. He commented then that he’d endured cloudy weather and sub-freezing temperatures in order to capture the images. “My fingers still hurt!” he wrote.

Mike Olason in Denver, Colorado captured 3200 Phaethon on December 4, 2017:

Image via Mike Olason.

The 2017 encounter was the closest this object will come to Earth until 2093.

3200 Phaethon swept close to Earth – jus 0.069 astronomical units (6.4 million miles, 10.3 million km, 26 lunar-distances) on December 16, 2017 at 23 UTC. Image via Osamu Ajiki (AstroArts)/ Ron Baalke (JPL)/Ade Ashford (AN)/AstronomyNow.

Artist’s concept of what asteroid 3200 Phaethon might look like close up. Notice its blue color and tail of dust. Image via Heather Roper/UANews.

Bottom line: 3200 Phaethon is a mysterious rock-comet and the source of the Geminid meteor shower.

See photos: With 3200 Phaethon nearby, 2017 was a grand year for the Geminids

Via U.S. Naval Research Lab

from EarthSky https://ift.tt/36tfYtd

View larger. | Look closely along the line of white dots. A faint dust trail is visible in places where the dots are omitted. This faint dust trail – left behind by 3200 Phaethon, parent body for the Geminid meteor shower – was captured for the first time by a camera called WISPR aboard the Parker Solar Probe. Image via Brendan Gallagher/ Guillermo Stenborg/ U.S. Naval Research Lab.

The 2019 Geminid meteor shower is happening now, and it peaks this weekend. Best morning is likely December 14, but try December 15, too; both mornings will feature a bright moon. As you may know, meteors in annual showers like the Geminids are the result of Earth’s encounter with trails of dust in space – called meteoroid streams by astronomers – left behind mainly by comets. The dust enters our atmosphere and vaporizes, producing the streaks of light we see as meteors or “shooting stars.” This week (December 11, 2019), astronomers at the U.S. Naval Research Laboratory held a press conference to discuss an actual image of a dust trail (above) left behind in space by the asteroid that spawned the Geminid meteor shower. It’s none other than mysterious 3200 Phaethon, an object of great interest and speculation.

Karl Battams – who goes by @SungrazerComets on Twitter – is a computational scientist the Naval Research Lab’s Space Science Division. At a NASA press conference on December 11, 2019, he discussed the new image, which comes from a Lab-built camera called WISPR. He said that 3200 Phaethon’s dust trail is best seen near the sun, where it’s most densely packed. And he said the data captured by WISPR determined the asteroid dust trail weighs an estimated billion tons, and measures more than 14 million miles (23 million km) long. He also said the findings raise questions about the trail’s origin:

Something catastrophic happened to Phaethon a couple of thousand years ago and created the Geminid meteor shower. There’s no way the asteroid is anywhere near active enough when it is near the sun to produce the mass of dust we are seeing …

Read more: NRL-camera aboard NASA spacecraft confirms asteroid phenomenon

And therein lies the essential mystery of 3200 Phaethon. Most meteor showers are spawned by comets. 3200 Phaethon is an asteroid. Comets are fragile, icy bodies that litter their orbits with debris. It’s easy to see how debris from a comet’s orbit can create a shower of meteors in Earth’s sky.

But a rocky asteroid? That’s tougher to understand.

Keep reading to learn more about mysterious 3200 Phaethon.

EarthSky lunar calendars are cool! They make great gifts. Order now. Going fast!

we were excited to see them from space as well!https://t.co/ejvkzcDpkK

— U.S. Naval Research Laboratory (@USNRL) December 11, 2019

3200 Phaethon is an odd color for an asteroid. Most asteroids are dull grey to red, depending on the type of material on their surface. 3200 Phaethon is blue. Blue asteroids are known, but make up only a fraction of all known asteroids. And Phaethon isn’t just blue. It’s one of the bluest of similarly-colored asteroids (or comets) in the solar system.

Here’s another odd feature of 3200 Phaethon. While comets tend to have more elliptical orbits, asteroid orbits are more circular. 3200 Phaethon’s orbit – which is now exceedingly well known – is highly elongated, reminiscent of some comets. Its orbit crosses the orbits of Mars, Earth, Venus and Mercury.

Orbital path of 3200 Phaethon, via SkyandTelescope.com. In 2017, 3200 Phaethon came closer to Earth than it will again until 2093. The Geminids are always a reliable shower, but the shower was extra special in 2017 because its parent object was nearby.

Plus its orbit brings 3200 Phaethon closer to the sun than any other named asteroid (though some smaller, unnamed asteroids come even closer). At its closest point, Phaethon is only 13 million miles (20.9 million km) from the sun. That’s less than half of Mercury’s closest distance. Its name honors this object’s relationship to the sun. In Greek mythology, Phaethon was the son of the sun god Helios.

3200 Phaethon’s orbit carries it so close to the sun that its surface heats up to about 1,500 degrees Fahrenheit (800 degrees C). That’s hot enough to melt aluminum.

It’s when it’s closest to the sun that 3200 Phaethon releases a tiny dust tail; that’s right, it’s a dust tail for an asteroid, one of only two known so far in our solar system. Scientists have said it’s possible the sun’s heat causes fractures, in much the same way a dry riverbed cracks in the afternoon heat.

Comets are known for their tails. 3200 Phaethon’s dust tail is one of the features of this object that blurs the line traditionally thought to set comets and asteroids apart.

This closeup image of 3200 Phaethon by NASA’s STEREO A spacecraft in 2017 shows a tail extending faintly toward lower left. Image via NASA/SkyandTelescope.com.

3200 Phaethon was the first asteroid to be discovered via spacecraft on October 11, 1983. Astronomers Simon F. Green and John K. Davies noticed it while searching Infrared Astronomical Satellite data for moving objects. Charles T. Kowal confirmed it optically and said it was asteroid-like in appearance. The object received the provisional designation 1983 TB. Two years later, in 1985, using the convention for naming asteroids, astronomers assigned it its asteroid number and name: 3200 Phaethon.

Before 3200 Phaethon, scientists linked all known meteor showers to active comets and not asteroids.

Thus 3200 Phaethon surprised them from the beginning, because – while it looked like an asteroid – it appeared to be the source of the annual Geminid meteor shower. Astronomers began calling 3200 Phaethon a comet-asteroid hybrid, an asteroid that behaves like a comet. Later, they began using the term rock-comet.

Radar images of 3200 Phaethon generated by astronomers at the Arecibo Observatory on December 17, 2017. Image via Wikipedia.

Astronomer Teddy Kareta of the University of Arizona’s Lunar and Planetary Laboratory has studied 3200 Phaethon. He commented in 2018:

[At first], the assumption was that Phaethon probably was a dead, burnt-out comet, but comets are typically red in color, and not blue. So, even though Phaethon’s highly eccentric orbit should scream ‘dead comet,’ it’s hard to say whether Phaethon is more like an asteroid or more like a dead comet.

The composition of 3200 Phaethon resembles that of asteroid 2 Pallas. Both are dark, B-type asteroids composed of materials that have been modified by water. The 1st in this series of Hubble images of 3200 Phaethon in 2017 is marked with the asteroid’s spin axis (top) and south pole. Image via B. E. Schmidt et. al/NASA/ESA/SkyandTelescope.com.

3200 Phaethon is classified as a potentially hazardous asteroid, which doesn’t mean it’s a threat to Earth. It just means two things. First, 3200 Phaethon is big – about 3 miles (5 km) wide – big enough to cause significant regional damage if it were to strike Earth.

Second, it’s known to make periodic close approaches to Earth.

The 2017 “close approach” brought this object to about 26 times the moon’s distance. Astronomers know of no upcoming strike by this object in this foreseeable future.

Both amateur and professional astronomers watched 3200 Phaethon as carefully as they could in 2017. For example, Northolt Branch Observatories in London, England, created the animation below from images it captured in 2017.

Steven Bellavia also produced a video of 3200 Phaethon in 2017 – below. He commented then that he’d endured cloudy weather and sub-freezing temperatures in order to capture the images. “My fingers still hurt!” he wrote.

Mike Olason in Denver, Colorado captured 3200 Phaethon on December 4, 2017:

Image via Mike Olason.

The 2017 encounter was the closest this object will come to Earth until 2093.

3200 Phaethon swept close to Earth – jus 0.069 astronomical units (6.4 million miles, 10.3 million km, 26 lunar-distances) on December 16, 2017 at 23 UTC. Image via Osamu Ajiki (AstroArts)/ Ron Baalke (JPL)/Ade Ashford (AN)/AstronomyNow.

Artist’s concept of what asteroid 3200 Phaethon might look like close up. Notice its blue color and tail of dust. Image via Heather Roper/UANews.

Bottom line: 3200 Phaethon is a mysterious rock-comet and the source of the Geminid meteor shower.

See photos: With 3200 Phaethon nearby, 2017 was a grand year for the Geminids

Via U.S. Naval Research Lab

from EarthSky https://ift.tt/36tfYtd

A year with 13 Friday the 13ths?

A month is based loosely on the cycle of the moon. Image via Tomruen/Wikimedia Commons.

Any calendar year has at least one Friday the 13th, and can have as many as three Friday the 13ths. This year, 2019, we have two: September 13 and December 13. However – should we ever choose to replace our standard Gregorian calendar with an International Fixed Calendar (more about it below) – we’d have 13 months in a single year, with each month featuring a Friday the 13th. That’d be 13 Friday the 13ths in one calendar year!

The month, of course, is an arbitrary concept, based loosely on the cycle of Earth’s companion moon. Months can be, and have been, many different lengths. In contrast to the Gregorian calendar, an International Fixed Calendar would be composed of 13 months, each of which would have 28 days (for a total of 364 days). With the International Fixed Calendar, weekday names would fall on the same dates each and every month. If your birthday was on a Monday one year, it’d be on a Monday every year. What this calendar system calls its Year Day would be a special day, existing outside of any week, inserted in between Saturday, December 28, and Sunday, January 1. Because Year Day would exist outside of any week or year, it’d be a holiday with no weekday name … to be celebrated as “a day out of time.”

Sound fun? Keep reading …

Of course, in a 13-month calendar system, we’d also have a new additional month. The International Fixed Calendar system calls this extra month Sol and requires that it fit between the months of June and July.

And what about leap years in the International Fixed Calendar? In a leap of year of 366 days, Leap Day would come one day after Saturday, June 28, and one day before Sunday, Sol 1. Like Year Day, Leap Day would reside outside of any week and therefore would have no weekday name.

Read more: Two Friday the 13ths in 2019

The lunar calendars are here! Get your 2020 lunar calendars today. They make great gifts. Going fast!

Every month in the 13-month calendar would harbor 28 days, with each month showcasing a Friday the 13th. Image via Wikipedia.

How likely are we to adopt the International Fixed Calendar? Not very likely. According to an article from CityLab.com:

Momentum behind the International Fixed Calendar, a 13-month calendar with 28 days in each month and a leftover day at the end of each year (it also followed the Gregorian rules with regards to Leap Years), was never stronger than in the late 1920s.

Similar to Auguste Comte’s positivist calendar (created in 1849), this particular 13-month invention came from the mind of Moses Cotsworth, a North Eastern Railway advisor bothered by inexplicably varying monthly earnings over the traditional 12-month period. Cotsworth’s plan quickly gained popularity among businessmen, especially in transportation and logistics. His biggest ally however, was photography pioneer and Kodak founder, George Eastman …

Read more from CityLab: The death and life of the 13-month calendar

The International Fixed Calendar of 13 months containing 28 days each. Note that all 13 months start on a Sunday and have a Friday the 13th. Illustration via CityLab.

Still, some people claim the 13-month calendar better synchronizes solar and lunar cycles, because the moon travels full circle in front of the constellations of the zodiac in about 27.3 days. (This 27.3-day period is known as the sidereal month.) Also, since the 28-day month corresponds to the mean length of the female menstrual cycle, the 13-month calendar is sometimes regarded as a feminine calendar.

On the other hand – still speaking of nature’s cycles here – the lunar (or synodic) month, which is based on the moon’s phases, lasts a solid two days longer than the 27.3-day sidereal month. The time period between successive full moons is about 29.5 days, which is about 1 1/2 days longer than the proposed 28-day calendar month.

So we’d lose our Blue Moons if we ever were to adopt the 13-month International Fixed Calendar. The second of two full moons in a single month is commonly called a Blue Moon. In this 13-month calendar, there wouldn’t be time in a single month for the moon to go from full, through all its phases, and back to full again.

But with this 13-month calendar, we’d certainly find calendar months having no full moon at all. In the 19-year Metonic cycle, we’d have 247 calendar months yet only 235 full moons, so somewhere around 12 calendar months would have no full moon in one 19-year period.

In our Gregorian calendar, only the month of February can have no full moon. This last happened in February 2018, and will next happen 19 years later, in February 2037.

Read more: Why no full moon in February 2018?

Now and again, I suppose, the International Fixed Calendar would actually find the full moon falling on Year Day or Leap Day, though I imagine quite rarely. Let me go out on the limb of modern folklore here and propose that a full moon happening outside of any week might be the International Fixed Calendar’s version of a Blue Moon!

The Gregorian dates between March and June are a day earlier during a Gregorian leap year. Image via Wikipedia.

Bottom line: The year 2019 presents a Friday the 13th in September and December. But should we ever switch over to the proposed 13-month calendar, we’d have a Friday the 13th every month.

from EarthSky https://ift.tt/30UlbHk

A month is based loosely on the cycle of the moon. Image via Tomruen/Wikimedia Commons.

Any calendar year has at least one Friday the 13th, and can have as many as three Friday the 13ths. This year, 2019, we have two: September 13 and December 13. However – should we ever choose to replace our standard Gregorian calendar with an International Fixed Calendar (more about it below) – we’d have 13 months in a single year, with each month featuring a Friday the 13th. That’d be 13 Friday the 13ths in one calendar year!

The month, of course, is an arbitrary concept, based loosely on the cycle of Earth’s companion moon. Months can be, and have been, many different lengths. In contrast to the Gregorian calendar, an International Fixed Calendar would be composed of 13 months, each of which would have 28 days (for a total of 364 days). With the International Fixed Calendar, weekday names would fall on the same dates each and every month. If your birthday was on a Monday one year, it’d be on a Monday every year. What this calendar system calls its Year Day would be a special day, existing outside of any week, inserted in between Saturday, December 28, and Sunday, January 1. Because Year Day would exist outside of any week or year, it’d be a holiday with no weekday name … to be celebrated as “a day out of time.”

Sound fun? Keep reading …

Of course, in a 13-month calendar system, we’d also have a new additional month. The International Fixed Calendar system calls this extra month Sol and requires that it fit between the months of June and July.

And what about leap years in the International Fixed Calendar? In a leap of year of 366 days, Leap Day would come one day after Saturday, June 28, and one day before Sunday, Sol 1. Like Year Day, Leap Day would reside outside of any week and therefore would have no weekday name.

Read more: Two Friday the 13ths in 2019

The lunar calendars are here! Get your 2020 lunar calendars today. They make great gifts. Going fast!

Every month in the 13-month calendar would harbor 28 days, with each month showcasing a Friday the 13th. Image via Wikipedia.

How likely are we to adopt the International Fixed Calendar? Not very likely. According to an article from CityLab.com:

Momentum behind the International Fixed Calendar, a 13-month calendar with 28 days in each month and a leftover day at the end of each year (it also followed the Gregorian rules with regards to Leap Years), was never stronger than in the late 1920s.

Similar to Auguste Comte’s positivist calendar (created in 1849), this particular 13-month invention came from the mind of Moses Cotsworth, a North Eastern Railway advisor bothered by inexplicably varying monthly earnings over the traditional 12-month period. Cotsworth’s plan quickly gained popularity among businessmen, especially in transportation and logistics. His biggest ally however, was photography pioneer and Kodak founder, George Eastman …

Read more from CityLab: The death and life of the 13-month calendar

The International Fixed Calendar of 13 months containing 28 days each. Note that all 13 months start on a Sunday and have a Friday the 13th. Illustration via CityLab.

Still, some people claim the 13-month calendar better synchronizes solar and lunar cycles, because the moon travels full circle in front of the constellations of the zodiac in about 27.3 days. (This 27.3-day period is known as the sidereal month.) Also, since the 28-day month corresponds to the mean length of the female menstrual cycle, the 13-month calendar is sometimes regarded as a feminine calendar.

On the other hand – still speaking of nature’s cycles here – the lunar (or synodic) month, which is based on the moon’s phases, lasts a solid two days longer than the 27.3-day sidereal month. The time period between successive full moons is about 29.5 days, which is about 1 1/2 days longer than the proposed 28-day calendar month.

So we’d lose our Blue Moons if we ever were to adopt the 13-month International Fixed Calendar. The second of two full moons in a single month is commonly called a Blue Moon. In this 13-month calendar, there wouldn’t be time in a single month for the moon to go from full, through all its phases, and back to full again.

But with this 13-month calendar, we’d certainly find calendar months having no full moon at all. In the 19-year Metonic cycle, we’d have 247 calendar months yet only 235 full moons, so somewhere around 12 calendar months would have no full moon in one 19-year period.

In our Gregorian calendar, only the month of February can have no full moon. This last happened in February 2018, and will next happen 19 years later, in February 2037.

Read more: Why no full moon in February 2018?

Now and again, I suppose, the International Fixed Calendar would actually find the full moon falling on Year Day or Leap Day, though I imagine quite rarely. Let me go out on the limb of modern folklore here and propose that a full moon happening outside of any week might be the International Fixed Calendar’s version of a Blue Moon!

The Gregorian dates between March and June are a day earlier during a Gregorian leap year. Image via Wikipedia.

Bottom line: The year 2019 presents a Friday the 13th in September and December. But should we ever switch over to the proposed 13-month calendar, we’d have a Friday the 13th every month.

from EarthSky https://ift.tt/30UlbHk

December brings 2019’s 2nd Friday the 13th

Image via les affaires.

Friday, December 13, 2019, gives us the second two Friday the 13ths this year. Exactly 13 weeks previous to this Friday the 13th, we had our first Friday the 13th on Friday, September 13, 2019. Unusual? Not particularly. Any calendar year has at least one Friday the 13th, and can have as many as three Friday the 13ths. Not that we at EarthSky suffer from friggatriskaidekaphobia – an irrational fear of Friday the 13th – but, gosh darn, the next Friday the 13th happens exactly 13 weeks after today’s Friday the 13th – coming on March 13, 2020.

Yikes, these few coincidences involving the number 13 are only the tip of the iceberg. We could cite more …

Keep reading to investigate the intriguing mathematics behind Friday the 13th and the calendar.

The last time we had only one Friday the 13th in a calendar year was in May 2016 and the next time won’t be until August 2021. Three Friday the 13ths last took place in 2015 (February, March, November), and will next happen in 2026 (February, March, November).

Read more: This year’s Harvest Moon on Friday, September 13, 2019

Gioachino Rossini, a 19th century Italian composer. Folklorists say there's no written evidence that Friday the 13th was considered unlucky before the 19th century. The earliest known documented reference in English appears to be in Henry Sutherland Edwards' 1869 biography of Rossini.

Are all these Friday the 13ths a super coincidence? Super unlucky? Neither. They’re just a quirk of our calendar.

According to folklorists, there’s no written evidence that Friday the 13th was considered unlucky before the 19th century. The earliest known documented reference in English appears to be in Henry Sutherland Edwards’ 1869 biography of Gioachino Rossini.

Still, Friday has always gotten a bad rap. In the Middle Ages, people would not marry – or set out on a journey – on a Friday.

There are also some links between Christianity and an ill association with either Fridays or the number 13. Jesus was said to be crucified on a Friday. Seating 13 people at a table was seen as bad luck because Judas Iscariot, the disciple who betrayed Jesus, is said to have been the 13th guest at the Last Supper. Meanwhile, our word for Friday comes from Frigga, an ancient Scandinavian fertility and love goddess. Christians called Frigga a witch and Friday the Witches’ Sabbath.

In modern times, the slasher-movie franchise “Friday the 13th” has helped keep friggatriskaidekaphobia alive.

The Friday the 13th slasher-movie franchise helped this day maintain its notoriety. Image via Wikimedia Commons.

We have two Friday the 13ths in 2019 – in September and December – because 2019 is a common year (not a leap year) that started on a Tuesday. Whenever a common year of 365 days starts on a Tuesday, it’s inevitable that the months of September and December will start on a Sunday. And any month starting on a Sunday will have a Friday the 13th.

The last time a common year started on a Tuesday was six years ago, in the year 2013, and the next time will be 11 years from 2019, in 2030.

In addition, when any leap year of 366 days begins on a Monday, there are Friday the 13ths in September and December, as well. This September-December Friday the 13th leap year will take place five years from now, in 2024.

Some of you may wonder if there’s some formula that governs how the Friday the 13th drama repeats itself. The answer is yes! Keep in mind that a twofold September-December Friday the 13th year can only happen during a common year of 365 days, when January 1 falls on a Tuesday – or in a leap year of 366 days, when January 1 falls on a Monday. Let the intriguing number play begin …

The first twofold September-December Friday the 13th year in the 21st century (2001 to 2100) occurred in 2002, which is two years after a leap year. Any calendar year happening two years after a leap year will have days and dates matching up again in periods of 11, 17 and 28 years:

2002 + 11 = 2013

2002 + 17 = 2019

2002 + 28 = 2030

September 2019 calendar via TimeandDate.

How often do September-December Friday the 13ths happen? More often than you might imagine! We continue the cycle onward to find a grand total of 11 September-December Friday the 13th 365-day common years for the 21st century (2001 to 2100):

2002, 2013, 2019, 2030, 2041, 2047, 2058, 2069, 2075, 2086 and 2097

In the 21st century (2001 to 2100), the first September-December Friday the 13th leap year of 366 days occurs in 2024. This September-December Friday the 13th leap year recurs in cycles of 28 years:

2024 + 28 = 2052

2052 + 28 = 2080

So we find a total of three September-December Friday the 13th leap years in the 21st century (2001 to 2100): 2024, 2052 and 2080.

Statistically speaking … the modal day for the 13th to occur on is Friday, with 688 occurrences in the 4,800-month cycle. (Of course, this is the same graph for the 6th as well as the 13th, 20th and 27th.) Caption and graphic via datagenetics.com.

Rhyme and reason for the 400-year Friday the 13th cycle.

Because the Gregorian calendar has a 400-year cycle, these twofold September-December Friday the 13th years recur in cycles of 400 years. For example, respective September-December Friday the 13th calendar years are exactly 400 years apart in the 21st and 25th centuries:

21st century (2001 to 2100):

2002, 2013, 2019, 2024 (leap year), 2030, 2041, 2047, 2052 (leap year), 2058, 2069, 2075, 2080 (leap year), 2086 and 2097

25th century (2401 to 2500):

2402, 2413, 2419, 2424 (leap year), 2430, 2441, 2447, 2452 (leap year), 2458, 2469, 2475, 2480 (leap year), 2486 and 2497

How about in other centuries? If you’re up for doing the computations:

22nd century (2101 to 2200): the first common year September-December Friday the 13th happens in 2109, and repeats in cycles of 6, 17 and 28 years. The first leap year September-December Friday the 13th happens in 2120 and recurs every 28 years.

23rd century (2201 to 2300): the first common September-December Friday the 13th year happens in 2205, and repeats every 6, 17 and 28 years. The first leap year September-December Friday the 13th happens in 2216 – but, by Gregorian calendar rules, the year 2300 is not a leap year.

24th century (2301 to 2400): the first common September-December Friday the 13th year happens in 2301, with the days and dates matching up again in periods of 6, 17 and 28 years. The first leap year September-December Friday the 13th happens in 2216.

Read more: A year with 13 Friday the 13ths?

As magical as all of this Friday the 13th calendar intrigue appears to be, it’s not supernatural. It’s entertaining number play, even if it may haunt our uncomprehending minds.

“… and whether or not it is clear to you, the universe is unfolding as it should.” Resin, acrylic paint and archival print on transparency on panel, by Boston artist Jessica Dunegan.

Bottom line: September 13, 2019, presents the first Friday the 13th in 2019. Then, exactly 13 weeks after that, 2019’s second Friday the 13th falls in December.

from EarthSky https://ift.tt/2PyeABK

Image via les affaires.

Friday, December 13, 2019, gives us the second two Friday the 13ths this year. Exactly 13 weeks previous to this Friday the 13th, we had our first Friday the 13th on Friday, September 13, 2019. Unusual? Not particularly. Any calendar year has at least one Friday the 13th, and can have as many as three Friday the 13ths. Not that we at EarthSky suffer from friggatriskaidekaphobia – an irrational fear of Friday the 13th – but, gosh darn, the next Friday the 13th happens exactly 13 weeks after today’s Friday the 13th – coming on March 13, 2020.

Yikes, these few coincidences involving the number 13 are only the tip of the iceberg. We could cite more …

Keep reading to investigate the intriguing mathematics behind Friday the 13th and the calendar.

The last time we had only one Friday the 13th in a calendar year was in May 2016 and the next time won’t be until August 2021. Three Friday the 13ths last took place in 2015 (February, March, November), and will next happen in 2026 (February, March, November).

Read more: This year’s Harvest Moon on Friday, September 13, 2019

Gioachino Rossini, a 19th century Italian composer. Folklorists say there's no written evidence that Friday the 13th was considered unlucky before the 19th century. The earliest known documented reference in English appears to be in Henry Sutherland Edwards' 1869 biography of Rossini.

Are all these Friday the 13ths a super coincidence? Super unlucky? Neither. They’re just a quirk of our calendar.

According to folklorists, there’s no written evidence that Friday the 13th was considered unlucky before the 19th century. The earliest known documented reference in English appears to be in Henry Sutherland Edwards’ 1869 biography of Gioachino Rossini.

Still, Friday has always gotten a bad rap. In the Middle Ages, people would not marry – or set out on a journey – on a Friday.

There are also some links between Christianity and an ill association with either Fridays or the number 13. Jesus was said to be crucified on a Friday. Seating 13 people at a table was seen as bad luck because Judas Iscariot, the disciple who betrayed Jesus, is said to have been the 13th guest at the Last Supper. Meanwhile, our word for Friday comes from Frigga, an ancient Scandinavian fertility and love goddess. Christians called Frigga a witch and Friday the Witches’ Sabbath.

In modern times, the slasher-movie franchise “Friday the 13th” has helped keep friggatriskaidekaphobia alive.

The Friday the 13th slasher-movie franchise helped this day maintain its notoriety. Image via Wikimedia Commons.

We have two Friday the 13ths in 2019 – in September and December – because 2019 is a common year (not a leap year) that started on a Tuesday. Whenever a common year of 365 days starts on a Tuesday, it’s inevitable that the months of September and December will start on a Sunday. And any month starting on a Sunday will have a Friday the 13th.

The last time a common year started on a Tuesday was six years ago, in the year 2013, and the next time will be 11 years from 2019, in 2030.

In addition, when any leap year of 366 days begins on a Monday, there are Friday the 13ths in September and December, as well. This September-December Friday the 13th leap year will take place five years from now, in 2024.

Some of you may wonder if there’s some formula that governs how the Friday the 13th drama repeats itself. The answer is yes! Keep in mind that a twofold September-December Friday the 13th year can only happen during a common year of 365 days, when January 1 falls on a Tuesday – or in a leap year of 366 days, when January 1 falls on a Monday. Let the intriguing number play begin …

The first twofold September-December Friday the 13th year in the 21st century (2001 to 2100) occurred in 2002, which is two years after a leap year. Any calendar year happening two years after a leap year will have days and dates matching up again in periods of 11, 17 and 28 years:

2002 + 11 = 2013

2002 + 17 = 2019

2002 + 28 = 2030

September 2019 calendar via TimeandDate.

How often do September-December Friday the 13ths happen? More often than you might imagine! We continue the cycle onward to find a grand total of 11 September-December Friday the 13th 365-day common years for the 21st century (2001 to 2100):

2002, 2013, 2019, 2030, 2041, 2047, 2058, 2069, 2075, 2086 and 2097

In the 21st century (2001 to 2100), the first September-December Friday the 13th leap year of 366 days occurs in 2024. This September-December Friday the 13th leap year recurs in cycles of 28 years:

2024 + 28 = 2052

2052 + 28 = 2080

So we find a total of three September-December Friday the 13th leap years in the 21st century (2001 to 2100): 2024, 2052 and 2080.

Statistically speaking … the modal day for the 13th to occur on is Friday, with 688 occurrences in the 4,800-month cycle. (Of course, this is the same graph for the 6th as well as the 13th, 20th and 27th.) Caption and graphic via datagenetics.com.

Rhyme and reason for the 400-year Friday the 13th cycle.

Because the Gregorian calendar has a 400-year cycle, these twofold September-December Friday the 13th years recur in cycles of 400 years. For example, respective September-December Friday the 13th calendar years are exactly 400 years apart in the 21st and 25th centuries:

21st century (2001 to 2100):

2002, 2013, 2019, 2024 (leap year), 2030, 2041, 2047, 2052 (leap year), 2058, 2069, 2075, 2080 (leap year), 2086 and 2097

25th century (2401 to 2500):

2402, 2413, 2419, 2424 (leap year), 2430, 2441, 2447, 2452 (leap year), 2458, 2469, 2475, 2480 (leap year), 2486 and 2497

How about in other centuries? If you’re up for doing the computations:

22nd century (2101 to 2200): the first common year September-December Friday the 13th happens in 2109, and repeats in cycles of 6, 17 and 28 years. The first leap year September-December Friday the 13th happens in 2120 and recurs every 28 years.

23rd century (2201 to 2300): the first common September-December Friday the 13th year happens in 2205, and repeats every 6, 17 and 28 years. The first leap year September-December Friday the 13th happens in 2216 – but, by Gregorian calendar rules, the year 2300 is not a leap year.

24th century (2301 to 2400): the first common September-December Friday the 13th year happens in 2301, with the days and dates matching up again in periods of 6, 17 and 28 years. The first leap year September-December Friday the 13th happens in 2216.

Read more: A year with 13 Friday the 13ths?

As magical as all of this Friday the 13th calendar intrigue appears to be, it’s not supernatural. It’s entertaining number play, even if it may haunt our uncomprehending minds.

“… and whether or not it is clear to you, the universe is unfolding as it should.” Resin, acrylic paint and archival print on transparency on panel, by Boston artist Jessica Dunegan.

Bottom line: September 13, 2019, presents the first Friday the 13th in 2019. Then, exactly 13 weeks after that, 2019’s second Friday the 13th falls in December.

from EarthSky https://ift.tt/2PyeABK

Amazon fires quickening glacier melting in Andes

Image via 3523studio/ shutterstock.

By Matthew Harris, Keele University

If you have turned on a TV or read the news during the past few months, you have probably heard of the widespread fires that wrought havoc on the Amazon rainforest this year. Fires occur in the rainforest every year, but the past 11 months saw the number of fires increase by more than 70% when compared with 2018, indicating a major acceleration in land clearing by the country’s logging and farming industries.

The smoke from the fires rose high into the atmosphere and could be seen from space. Some regions of Brazil became covered in thick smoke that closed airports and darkened city skies.

As the rainforest burns, it releases enormous amounts of carbon dioxide, carbon monoxide, and larger particles of so-called “black carbon” (smoke and soot). The phrase “enormous amounts” hardly does the numbers justice – in any given year, the burning of forests and grasslands in South America emits a whopping 800,000 tonnes (880,000 U.S. tons) of black carbon into the atmosphere.

This truly astounding amount is almost double the black carbon produced by all combined energy use in Europe over 12 months. Not only does this absurd amount of smoke cause health issues and contribute to global warming but, as a growing number of scientific studies are showing, it also more directly contributes to the melting of glaciers.

In a new paper published November 28, 2019, in the journal Scientific Reports, a team of researchers has outlined how smoke from fires in the Amazon in 2010 made glaciers in the Andes melt more quickly.

EarthSky 2020 lunar calendars are available! They make great gifts. Order now. Going fast!

South America: the Andes mountains run along the western edge of the Amazon basin (center). Image via AridOcean/ shutterstock.

When fires in the Amazon emit black carbon during the peak burning season (August to October), winds carry these clouds of smoke to Andean glaciers, which can sit higher than 3 miles (5,000 meters) above sea level.

Despite being invisible to the naked eye, black carbon particles affect the ability of the snow to reflect incoming sunlight, a phenomenon known as albedo. Similar to how a dark-colored car will heat up more quickly in direct sunlight when compared with a light-colored one, glaciers covered by black carbon particles will absorb more heat, and thus melt faster.

By using a computer simulation of how particles move through the atmosphere, known as HYSPLIT, the team was able to show that smoke plumes from the Amazon are carried by winds to the Andes, where they fall as an invisible mist across glaciers. Altogether, they found that fires in the Amazon in 2010 caused a 4.5% increase in water runoff from Zongo Glacier in Bolivia.

The Zongo glacier is found on the slopes of Huayna Potosi, one of Bolivia’s highest mountains. Image via Ryan Michael Wilson/ shutterstock.

Crucially, the authors also found that the effect of black carbon depends on the amount of dust covering a glacier – if the amount of dust is higher, then the glacier will already be absorbing most of the heat that might have been absorbed by the black carbon. Land clearing is one of the reasons that dust levels over South America doubled during the 20th century.

Glaciers are some of the most important natural resources on the planet. Himalayan glaciers provide drinking water for 240 million people, and 1.9 billion rely on them for food. In South America, glaciers are crucial for water supply – in some towns, including Huaraz in Peru, more than 85% of drinking water comes from glaciers during times of drought. However, these truly vital sources of water are increasingly under threat as the planet feels the effects of global warming. Glaciers in the Andes have been receding rapidly for the last 50 years.

The tropical belt of South America is predicted to become more dry and arid as the climate changes. A drier climate means more dust, and more fires. It also means more droughts, which make towns more reliant on glaciers for water.

Unfortunately, as the above study shows, the fires assisted by dry conditions help to make these vital sources of water vanish more quickly. The role of black carbon in glacier melting is an exceedingly complex process – currently, the climate models used to predict the future melting of glaciers in the Andes do not incorporate black carbon. As the authors of this new study show, this is likely causing the rate of glacial melt to be underestimated in many current assessments.

With communities reliant on glaciers for water, and these same glaciers likely to melt faster as the climate warms, work examining complex forces like black carbon and albedo changes is needed more now than ever before.

Matthew Harris, Ph.D. Researcher, Climate Science, Keele University

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

Bottom line: Wildfires in the Amazon are quickening glacial melt in the Andes Mountains.

from EarthSky https://ift.tt/35fgdb7

Image via 3523studio/ shutterstock.

By Matthew Harris, Keele University

If you have turned on a TV or read the news during the past few months, you have probably heard of the widespread fires that wrought havoc on the Amazon rainforest this year. Fires occur in the rainforest every year, but the past 11 months saw the number of fires increase by more than 70% when compared with 2018, indicating a major acceleration in land clearing by the country’s logging and farming industries.

The smoke from the fires rose high into the atmosphere and could be seen from space. Some regions of Brazil became covered in thick smoke that closed airports and darkened city skies.

As the rainforest burns, it releases enormous amounts of carbon dioxide, carbon monoxide, and larger particles of so-called “black carbon” (smoke and soot). The phrase “enormous amounts” hardly does the numbers justice – in any given year, the burning of forests and grasslands in South America emits a whopping 800,000 tonnes (880,000 U.S. tons) of black carbon into the atmosphere.

This truly astounding amount is almost double the black carbon produced by all combined energy use in Europe over 12 months. Not only does this absurd amount of smoke cause health issues and contribute to global warming but, as a growing number of scientific studies are showing, it also more directly contributes to the melting of glaciers.

In a new paper published November 28, 2019, in the journal Scientific Reports, a team of researchers has outlined how smoke from fires in the Amazon in 2010 made glaciers in the Andes melt more quickly.

EarthSky 2020 lunar calendars are available! They make great gifts. Order now. Going fast!

South America: the Andes mountains run along the western edge of the Amazon basin (center). Image via AridOcean/ shutterstock.

When fires in the Amazon emit black carbon during the peak burning season (August to October), winds carry these clouds of smoke to Andean glaciers, which can sit higher than 3 miles (5,000 meters) above sea level.

Despite being invisible to the naked eye, black carbon particles affect the ability of the snow to reflect incoming sunlight, a phenomenon known as albedo. Similar to how a dark-colored car will heat up more quickly in direct sunlight when compared with a light-colored one, glaciers covered by black carbon particles will absorb more heat, and thus melt faster.

By using a computer simulation of how particles move through the atmosphere, known as HYSPLIT, the team was able to show that smoke plumes from the Amazon are carried by winds to the Andes, where they fall as an invisible mist across glaciers. Altogether, they found that fires in the Amazon in 2010 caused a 4.5% increase in water runoff from Zongo Glacier in Bolivia.

The Zongo glacier is found on the slopes of Huayna Potosi, one of Bolivia’s highest mountains. Image via Ryan Michael Wilson/ shutterstock.

Crucially, the authors also found that the effect of black carbon depends on the amount of dust covering a glacier – if the amount of dust is higher, then the glacier will already be absorbing most of the heat that might have been absorbed by the black carbon. Land clearing is one of the reasons that dust levels over South America doubled during the 20th century.

Glaciers are some of the most important natural resources on the planet. Himalayan glaciers provide drinking water for 240 million people, and 1.9 billion rely on them for food. In South America, glaciers are crucial for water supply – in some towns, including Huaraz in Peru, more than 85% of drinking water comes from glaciers during times of drought. However, these truly vital sources of water are increasingly under threat as the planet feels the effects of global warming. Glaciers in the Andes have been receding rapidly for the last 50 years.

The tropical belt of South America is predicted to become more dry and arid as the climate changes. A drier climate means more dust, and more fires. It also means more droughts, which make towns more reliant on glaciers for water.

Unfortunately, as the above study shows, the fires assisted by dry conditions help to make these vital sources of water vanish more quickly. The role of black carbon in glacier melting is an exceedingly complex process – currently, the climate models used to predict the future melting of glaciers in the Andes do not incorporate black carbon. As the authors of this new study show, this is likely causing the rate of glacial melt to be underestimated in many current assessments.

With communities reliant on glaciers for water, and these same glaciers likely to melt faster as the climate warms, work examining complex forces like black carbon and albedo changes is needed more now than ever before.

Matthew Harris, Ph.D. Researcher, Climate Science, Keele University

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

Bottom line: Wildfires in the Amazon are quickening glacial melt in the Andes Mountains.

from EarthSky https://ift.tt/35fgdb7

Aries? Here’s your constellation

The constellation Aries the Ram. His head is turned backward, looking in the direction of the Pleaides star cluster. Image via Old Book Art image Gallery

The sun – as seen from Earth – passes in front of the constellation Aries the Ram from about April 19 to May 14 every year. That’s why a Northern Hemisphere spring or Southern Hemisphere autumn presents the wrong time of year for viewing the constellation Aries because then the mighty Ram is lost in the sun’s glare. December is an especially good months for viewing Aries.

Sky chart of the constellation Aries the Ram, showing the Pleiades star cluster near the Pisces/Taurus border. Click here for a larger chart

Look for Cassiopeia high over Polaris, the North Star around 8 p.m. local time in early December and 6 p.m. in early January. Then use Cassiopeia to star-hop to Aries by drawing an imaginary line from Polaris, the North Star, and through the star Segin (Epsilon Cassiopeiae).

Not sure how to find the North Star with respect to Cassiopeia in December and January? This chart should help.

Best time for seeing Aries the Ram. The best time to behold the Mighty Ram is at the opposite end of the year, when the Earth is on the other side of the sun. In late October, this constellation rises in the east at sunset, reaches its highest point in the sky at midnight and sets in the west at sunrise.

November and December are especially good months for viewing Aries the Ram in all his starlit majesty, for this constellation shines above the eastern horizon at nightfall and stays out for most of the night. Aries culminates – reaches its highest point in the sky – at about 10 p.m. local time (the time in all time zones) in late November, 8 p.m. local time in late December and 6 p.m. local time in late January.

Aries is not a particularly prominent constellation, so a dark country sky absent of moonlight is most desirable for viewing the Ram at its finest. The three stars depicting the Ram’s bust – Hamal, Sheratan and Mesartim – suddenly brighten in a dark sky, as if someone had turned up the dimmer switch. By the way, a small telescope reveals that Mesartim is a double star.

Fortunately, the head of the Ram is fairly easy to locate. You’ll find it midway between these two signposts: the Pleiades star cluster to the east and the Square of Pegasus to the west. The Ram’s head is actually turned backward, as if admiring the Pleiades – or perhaps his own golden fleece.

You can also star-hop to Aries by drawing an imaginary line from Polaris, the North Star, and through a certain star in the constellation Cassiopeia: Segin (Epsilon Cassiopeiae). You’re seeking for the star at the east end of the famed starlit W or M, as shown on the sky chart at right. It’s a very long hop, more than twice the Polairs/Segin distance. Jump until you land between the Pleiades cluster and the Square of Pegasus.

By definition, the sun resides at the First Point of Aries on the March equinox. This point has a declination of zero degrees and a right ascension of zero degrees. The ecliptic and celestial equator intersect on the March and September equinoxes, and the celestial equator is equal to a declination of 0^o. Image via Wikimedia Commons

What is the First Point of Aries? The First Point of Aries marks the sun’s position in front of the constellations of the Zodiac on the Northern Hemisphere’s spring equinox or Southern Hemisphere’s autumnal equinox. This equinox happens yearly on or near March 20, as the sun crosses the celestial equator, going from south to north.

The First Point of Aries, which is actually in the constellation Pisces nowadays, defines the coordinate system on the celestial sphere. The First Point of Aries always coincides with 0^o right ascension and 0^o declination. Right ascension is the equivalent of longitude here on Earth. Declination on the sky’s dome is the equivalent of latitude.

The First Point of Aries is one of two places on the celestial sphere where the ecliptic and celestial equator intersect. The First Point of Libra resides 180^o east of the First Point of Aries, marking the September equinox point on the celestial sphere.

Because the Earth’s rotational axis wobbles full circle relative to the backdrop stars in about 26,000 years, Polaris doesn’t remain the North Star forever and the equinox points don’t remain fixed relative to the stars of the Zodiac. The March equinox point drifts westward (along the ecliptic) through the constellations of the Zodiac at about one degree (two sun diameters) in 72 years or 30^o in 2160 years.

Hence, the March equinox point passed out of the constellation Aries and into the constellation Pisces in 68 B.C. Even so, we still call this equinox point the First Point of Aries.

Hamal, ancient equinox star

Map showing the ancient Kingdom of Colchis on the eastern shore of the Black Sea. View larger.

Aries the Ram in star lore. In Greek mythology, Aries represents the supernatural Ram that was sent by Zeus to rescue the children of Athamus, the King of Thebes, from political intrigue. Phrixus and his sister Helle were about to meet their demise, but the flying Ram, which could both speak and reason, took them away in the nick of time.

The children held on tight as the Ram flew them away for the safety of Colchis, an ancient kingdom bordering the eastern shore of the Black Sea. Unfortunately, Helle fell into the sea and drowned before reaching their destination. Hellespont – the ancient name for the Dardanelles straight near Istanbul, Turkey – marks the place of her death and was named in her honor.

Phrixus survived the long trip to Colchis. He gave thanks by sacrificing the Ram to Zeus, hanging it in a sacred grove where the fleece turned to gold. Later on, Jason and the Argonauts recovered the Golden Fleece.

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

Bottom line: How to see the constellation Aries the Ram, plus info about this constellation in the history of astronomy and mythology.

Taurus? Here’s your constellation
Gemini? Here’s your constellation
Cancer? Here’s your constellation
Leo? Here’s your constellation
Virgo? Here’s your constellation
Libra? Here’s your constellation
Scorpius? Here’s your contellation
Sagittarius? Here’s your constellation
Capricornus? Here’s your constellation
Aquarius? Here’s your constellation
Pisces? Here’s your constellation
Aries? Here’s your constellation
Birthday late November to early December? Here’s your constellation

from EarthSky https://ift.tt/2qJWZeB

The constellation Aries the Ram. His head is turned backward, looking in the direction of the Pleaides star cluster. Image via Old Book Art image Gallery

The sun – as seen from Earth – passes in front of the constellation Aries the Ram from about April 19 to May 14 every year. That’s why a Northern Hemisphere spring or Southern Hemisphere autumn presents the wrong time of year for viewing the constellation Aries because then the mighty Ram is lost in the sun’s glare. December is an especially good months for viewing Aries.

Sky chart of the constellation Aries the Ram, showing the Pleiades star cluster near the Pisces/Taurus border. Click here for a larger chart

Look for Cassiopeia high over Polaris, the North Star around 8 p.m. local time in early December and 6 p.m. in early January. Then use Cassiopeia to star-hop to Aries by drawing an imaginary line from Polaris, the North Star, and through the star Segin (Epsilon Cassiopeiae).

Not sure how to find the North Star with respect to Cassiopeia in December and January? This chart should help.

Best time for seeing Aries the Ram. The best time to behold the Mighty Ram is at the opposite end of the year, when the Earth is on the other side of the sun. In late October, this constellation rises in the east at sunset, reaches its highest point in the sky at midnight and sets in the west at sunrise.

November and December are especially good months for viewing Aries the Ram in all his starlit majesty, for this constellation shines above the eastern horizon at nightfall and stays out for most of the night. Aries culminates – reaches its highest point in the sky – at about 10 p.m. local time (the time in all time zones) in late November, 8 p.m. local time in late December and 6 p.m. local time in late January.

Aries is not a particularly prominent constellation, so a dark country sky absent of moonlight is most desirable for viewing the Ram at its finest. The three stars depicting the Ram’s bust – Hamal, Sheratan and Mesartim – suddenly brighten in a dark sky, as if someone had turned up the dimmer switch. By the way, a small telescope reveals that Mesartim is a double star.

Fortunately, the head of the Ram is fairly easy to locate. You’ll find it midway between these two signposts: the Pleiades star cluster to the east and the Square of Pegasus to the west. The Ram’s head is actually turned backward, as if admiring the Pleiades – or perhaps his own golden fleece.

You can also star-hop to Aries by drawing an imaginary line from Polaris, the North Star, and through a certain star in the constellation Cassiopeia: Segin (Epsilon Cassiopeiae). You’re seeking for the star at the east end of the famed starlit W or M, as shown on the sky chart at right. It’s a very long hop, more than twice the Polairs/Segin distance. Jump until you land between the Pleiades cluster and the Square of Pegasus.

By definition, the sun resides at the First Point of Aries on the March equinox. This point has a declination of zero degrees and a right ascension of zero degrees. The ecliptic and celestial equator intersect on the March and September equinoxes, and the celestial equator is equal to a declination of 0^o. Image via Wikimedia Commons

What is the First Point of Aries? The First Point of Aries marks the sun’s position in front of the constellations of the Zodiac on the Northern Hemisphere’s spring equinox or Southern Hemisphere’s autumnal equinox. This equinox happens yearly on or near March 20, as the sun crosses the celestial equator, going from south to north.

The First Point of Aries, which is actually in the constellation Pisces nowadays, defines the coordinate system on the celestial sphere. The First Point of Aries always coincides with 0^o right ascension and 0^o declination. Right ascension is the equivalent of longitude here on Earth. Declination on the sky’s dome is the equivalent of latitude.

The First Point of Aries is one of two places on the celestial sphere where the ecliptic and celestial equator intersect. The First Point of Libra resides 180^o east of the First Point of Aries, marking the September equinox point on the celestial sphere.

Because the Earth’s rotational axis wobbles full circle relative to the backdrop stars in about 26,000 years, Polaris doesn’t remain the North Star forever and the equinox points don’t remain fixed relative to the stars of the Zodiac. The March equinox point drifts westward (along the ecliptic) through the constellations of the Zodiac at about one degree (two sun diameters) in 72 years or 30^o in 2160 years.

Hence, the March equinox point passed out of the constellation Aries and into the constellation Pisces in 68 B.C. Even so, we still call this equinox point the First Point of Aries.

Hamal, ancient equinox star

Map showing the ancient Kingdom of Colchis on the eastern shore of the Black Sea. View larger.

Aries the Ram in star lore. In Greek mythology, Aries represents the supernatural Ram that was sent by Zeus to rescue the children of Athamus, the King of Thebes, from political intrigue. Phrixus and his sister Helle were about to meet their demise, but the flying Ram, which could both speak and reason, took them away in the nick of time.

The children held on tight as the Ram flew them away for the safety of Colchis, an ancient kingdom bordering the eastern shore of the Black Sea. Unfortunately, Helle fell into the sea and drowned before reaching their destination. Hellespont – the ancient name for the Dardanelles straight near Istanbul, Turkey – marks the place of her death and was named in her honor.

Phrixus survived the long trip to Colchis. He gave thanks by sacrificing the Ram to Zeus, hanging it in a sacred grove where the fleece turned to gold. Later on, Jason and the Argonauts recovered the Golden Fleece.

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

Bottom line: How to see the constellation Aries the Ram, plus info about this constellation in the history of astronomy and mythology.

Taurus? Here’s your constellation
Gemini? Here’s your constellation
Cancer? Here’s your constellation
Leo? Here’s your constellation
Virgo? Here’s your constellation
Libra? Here’s your constellation
Scorpius? Here’s your contellation
Sagittarius? Here’s your constellation
Capricornus? Here’s your constellation
Aquarius? Here’s your constellation
Pisces? Here’s your constellation
Aries? Here’s your constellation
Birthday late November to early December? Here’s your constellation

from EarthSky https://ift.tt/2qJWZeB

Geminid meteors to peak this weekend

Image top of post: Geminid meteor radiant point by Greg Smye-Rumsby/Astronomy Now/Royal Astronomical Society

The annual Geminid meteor shower is expected to reach its peak this weekend – though under the glaring light of the almost-full waning gibbous moon. The peak morning is likely to be Saturday, December 14, 2019 – or, possibly, Sunday, December 15, 2019. But the morning of December 13 might offer some meteors, too. These colorful meteors tend to be bright, so you might see as many as 20 or so Perseids per hour, despite the moonlight. On a dark night, free of moonlight, you can easily spot 50 or more meteors per hour.

Just know that – although this is one shower you can successfully watch in the (late) evening – the best viewing is typically around 2 a.m., no matter where you are on Earth.

Want to see 2018’s brightest comet? How to see comet 46P/Wirtanen

Veteran meteor photographer Eliot Herman in Tucson, Arizona, captured this Geminid meteor flying from the radiant point on December 8, 2018. Note that the inset is our radiant point chart, shown at the top of this post. Thanks, Eliot!

The Geminids radiate from near bright Castor in the constellation Gemini, in the east on December evenings. Read more.

So the best time of night to watch for Geminid meteors is around 2 a.m., when the the shower’s radiant point – near the bright star Castor in the constellation Gemini – is high in the sky.

If you’re not one to stay up late, you can watch for meteors during the evening hours. Although the meteors will be few and far between at early-to-mid evening, you might, if you’re lucky, catch an earthgrazer – a sloow-moving and loong-lasting meteor that travels horizontally across the sky.

Can you watch the meteor shower online? Yes. It won’t be the same experience as being out under a dark country sky. But, especially if you’re clouded out and can’t get out of the city, watching online can be a good way to join the fun. So far, we’ve heard from only one organization planning to broadcast the Geminids live. It’s sky-live.tv, which will cover the live event with 3 cameras in Teide Observatory (Canary Islands), Olivenza (Extremadura) and High Energy Observatory HESS (Namibia).

The narration will be in Spanish. Find the live broadcast here: https://www.youtube.com/embed/LHuT5yDtDu0.

English speakers might like sky-live.tv’s Sky Cam for the Geminids, which has no narration: https://www.youtube.com/embed/mFUBpGEjY54.

Can you watch from the Southern Hemisphere? Sure! At temperate latitudes in the Southern Hemisphere, the meteors tend to be fewer. The Geminids do favor the Northern Hemisphere, where the radiant appears higher in the sky. However, this shower is also visible from the tropical and subtropical parts of the Southern Hemisphere.

How many meteors will you see? The Geminids are a consistent and prolific shower, but the numbers of meteors you see also strongly depends on your sky conditions and on how far you are from city lights. Often, in the hours after midnight and under a dark sky, you can see 50 or more meteors per hour. Rates of 120 per hour have been reported at the peak, under optimum sky conditions.

In 2019, moonlight will obtrude on this year’s production. How many will you see? Hard to say for sure! Just watch, and let us know.

Remember … meteors in annual showers typically come in spurts and lulls, so give yourself at least an hour of observing time. Simply sprawl out on a reclining lawn chair, look upward and enjoy the show.

Where do the meteors come from? Although meteors are sometimes called “shooting stars,” they have nothing to do with stars. Instead, they are strictly a solar system phenomenon. Around this time every year, our planet Earth crosses the orbital path of a mysterious object called 3200 Phaethon, which might be an asteroid or a burnt-out comet orbiting our sun.

Orbital path of 3200 Phaethon, the parent object of the Geminid meteors, via skyandtelescope.com

Debris from this object burns up in the Earth’s upper atmosphere to give us the annual Geminid meteor shower. Read more about 3200 Phaethon, the Geminid’s parent object.

EarthSky lunar calendars are cool! They make great gifts. Order now. Going fast!

John Ashley in Glacier National Park, Montana, caught this amazing earthgrazer meteor on December 6, 2018. Earthgrazers are best seen in the evening hours. Watch for them during this week’s Geminid meteor shower! John said this one lasted approximately 4 seconds and left behind a glowing smoke train that lasted at least 24 minutes. He commented: “The meteor went dark just above Dusty Star Mountain, or ‘Iszika-kakatosi’ in Blackfeet, which translates to ‘smoking star.'” Cool! Thanks, John! Nikon D750, Rokinon 24mm lens @ f1.4, 30 sec, ISO 3200.

Bottom line: With the moon out nearly all night long, this year’s Geminid meteor shower will be marred by moonlight. Peak morning is probably December 14, but watch December 13 and 15, too. You might catch some bright Geminids overcoming the moonlit glare!

Read more: 10 tips for watching the Geminids

Read more: Find the Geminid meteors’ radiant point

Read more: All you need to know about the Geminid meteor shower

from EarthSky https://ift.tt/2QIqicy

Image top of post: Geminid meteor radiant point by Greg Smye-Rumsby/Astronomy Now/Royal Astronomical Society

The annual Geminid meteor shower is expected to reach its peak this weekend – though under the glaring light of the almost-full waning gibbous moon. The peak morning is likely to be Saturday, December 14, 2019 – or, possibly, Sunday, December 15, 2019. But the morning of December 13 might offer some meteors, too. These colorful meteors tend to be bright, so you might see as many as 20 or so Perseids per hour, despite the moonlight. On a dark night, free of moonlight, you can easily spot 50 or more meteors per hour.

Just know that – although this is one shower you can successfully watch in the (late) evening – the best viewing is typically around 2 a.m., no matter where you are on Earth.

Want to see 2018’s brightest comet? How to see comet 46P/Wirtanen

Veteran meteor photographer Eliot Herman in Tucson, Arizona, captured this Geminid meteor flying from the radiant point on December 8, 2018. Note that the inset is our radiant point chart, shown at the top of this post. Thanks, Eliot!

The Geminids radiate from near bright Castor in the constellation Gemini, in the east on December evenings. Read more.

So the best time of night to watch for Geminid meteors is around 2 a.m., when the the shower’s radiant point – near the bright star Castor in the constellation Gemini – is high in the sky.

If you’re not one to stay up late, you can watch for meteors during the evening hours. Although the meteors will be few and far between at early-to-mid evening, you might, if you’re lucky, catch an earthgrazer – a sloow-moving and loong-lasting meteor that travels horizontally across the sky.

Can you watch the meteor shower online? Yes. It won’t be the same experience as being out under a dark country sky. But, especially if you’re clouded out and can’t get out of the city, watching online can be a good way to join the fun. So far, we’ve heard from only one organization planning to broadcast the Geminids live. It’s sky-live.tv, which will cover the live event with 3 cameras in Teide Observatory (Canary Islands), Olivenza (Extremadura) and High Energy Observatory HESS (Namibia).

The narration will be in Spanish. Find the live broadcast here: https://www.youtube.com/embed/LHuT5yDtDu0.

English speakers might like sky-live.tv’s Sky Cam for the Geminids, which has no narration: https://www.youtube.com/embed/mFUBpGEjY54.

Can you watch from the Southern Hemisphere? Sure! At temperate latitudes in the Southern Hemisphere, the meteors tend to be fewer. The Geminids do favor the Northern Hemisphere, where the radiant appears higher in the sky. However, this shower is also visible from the tropical and subtropical parts of the Southern Hemisphere.

How many meteors will you see? The Geminids are a consistent and prolific shower, but the numbers of meteors you see also strongly depends on your sky conditions and on how far you are from city lights. Often, in the hours after midnight and under a dark sky, you can see 50 or more meteors per hour. Rates of 120 per hour have been reported at the peak, under optimum sky conditions.

In 2019, moonlight will obtrude on this year’s production. How many will you see? Hard to say for sure! Just watch, and let us know.

Remember … meteors in annual showers typically come in spurts and lulls, so give yourself at least an hour of observing time. Simply sprawl out on a reclining lawn chair, look upward and enjoy the show.

Where do the meteors come from? Although meteors are sometimes called “shooting stars,” they have nothing to do with stars. Instead, they are strictly a solar system phenomenon. Around this time every year, our planet Earth crosses the orbital path of a mysterious object called 3200 Phaethon, which might be an asteroid or a burnt-out comet orbiting our sun.

Orbital path of 3200 Phaethon, the parent object of the Geminid meteors, via skyandtelescope.com

Debris from this object burns up in the Earth’s upper atmosphere to give us the annual Geminid meteor shower. Read more about 3200 Phaethon, the Geminid’s parent object.

EarthSky lunar calendars are cool! They make great gifts. Order now. Going fast!

John Ashley in Glacier National Park, Montana, caught this amazing earthgrazer meteor on December 6, 2018. Earthgrazers are best seen in the evening hours. Watch for them during this week’s Geminid meteor shower! John said this one lasted approximately 4 seconds and left behind a glowing smoke train that lasted at least 24 minutes. He commented: “The meteor went dark just above Dusty Star Mountain, or ‘Iszika-kakatosi’ in Blackfeet, which translates to ‘smoking star.'” Cool! Thanks, John! Nikon D750, Rokinon 24mm lens @ f1.4, 30 sec, ISO 3200.

Bottom line: With the moon out nearly all night long, this year’s Geminid meteor shower will be marred by moonlight. Peak morning is probably December 14, but watch December 13 and 15, too. You might catch some bright Geminids overcoming the moonlit glare!

Read more: 10 tips for watching the Geminids

Read more: Find the Geminid meteors’ radiant point

Read more: All you need to know about the Geminid meteor shower

from EarthSky https://ift.tt/2QIqicy

Explained! Enceladus’ enigmatic tiger stripes

View of Saturn’s moon Enceladus via the Cassini spacecraft. You can see the bluish tiger stripes on the moon’s left side. This image is tilted; the tiger stripes are at the moon’s south pole. Active geysers are erupting from the stripes even as we speak! Image via NASA/ ESA/ JPL/ SSI/ Cassini Imaging Team/ Carnegie Science.

Saturn’s moon Enceladus is one of the most fascinating worlds in our solar system. It has a subsurface water ocean and huge geyser-like plumes of vapor. The geysers erupt at the moon’s south pole through large cracks in Enceladus’ icy crust. These fissures – known to scientists as tiger stripes – have been one of the most distinctive and puzzling features of the moon since the Cassini spacecraft first spied them in 2005. Scientists have wanted to know … how did the tiger stripes form? Why are they parallel? And why are they so evenly spaced? Now they think they have some answers.

A new peer-reviewed study from the Carnegie Institution for Science, published in Nature Astronomy on December 9, 2019, is helping to explain the weird physics behind Enceladus’ curious tiger stripes. The findings were announced by Carnegie Science on the same day.

In a statement about the results, lead author Doug Hemingway said:

First seen by the Cassini mission to Saturn, these stripes are like nothing else known in our solar system. They are parallel and evenly spaced, about 130 kilometers long and 35 kilometers apart [about 80 miles and 20 miles apart]. What makes them especially interesting is that they are continually erupting with water ice, even as we speak. No other icy planets or moons have anything quite like them.

EarthSky 2020 lunar calendars are available! They make great gifts. Order now. Going fast!

A closer view of the mysterious tiger stripes on Enceladus. Image via NASA/ ESA/ JPL/ SSI/ Cassini Imaging Team/ Gizmodo.

Along with Max Rudolph of the University of California, Davis and Michael Manga of UC Berkeley, Hemingway used computer models to try to determine how the stripes form and how they remain in place for so long.

The study addressed questions regarding two odd features of the stripes in particular: why they are only located at the south pole of Enceladus and why they are as parallel and evenly spaced as they are.

As to the first question, the researchers found that the stripes could probably have formed at either the south or north pole. This could have occurred at either pole first, it just happened to be the south pole in this case.

Enceladus’ ice crust is thinnest over the poles, so it makes sense that this is where such cracks would tend to develop. This is due to the fact that the poles experience the greatest amount of deformation caused by Saturn’s powerful gravitational pull. When the water below the ice partially freezes during periods of gradual cooling, the ice crust will thicken from below. This causes pressure to increase until the ice splits open, creating a fissure, or stripe.

Illustration depicting the interior of Enceladus. Water from the subsurface ocean percolates to the surface through cracks in the ice at the south pole, erupting in huge plumes. Image via NASA/ JPL-Caltech.

The geysers of Saturn’s moon Enceladus. These huge plumes of water vapor erupt through cracks at Enceladus’ south pole. The Cassini spacecraft analyzed the plumes and found they contain water vapor, ice particles, salts, methane and a variety of complex organic molecules. Scientists believe they originate from an ocean below the moon’s icy crust. Image via NASA/ JPL-Caltech/ Space Science Institute.

The repeated deformation, or stretching of the crust, creates internal heat and keeps Enceladus’ ocean from completely freezing.

But why are the stripes parallel and equally spaced apart? The new study answers that question, Rudolph said:

Our model explains the regular spacing of the cracks.

The researchers think that the fissure called Baghdad Sulcus formed first. It remained open instead of freezing shut again, which allowed ocean water to spew out from the crevasse. Ice and snow – from jets of water that erupted from the ocean below and then froze and fell back down on the surface – had built up along the edges of the Baghdad Sulcus fissure, the weight of which created additional fissures. Rudolph said:

That caused the ice sheet to flex just enough to set off a parallel crack about 35 km away.

The same gravitational tidal effects that helps create the stripes also keeps them open. The fissures are like open wounds in Enceladus’ crust that never heal. The cracks repeatedly widen and narrow again, flushing water out in the process.

This is also partly thanks to Enceladus’ small size; if the noon was significantly larger, its gravity would prevent the fissures from re-opening.

Doug Hemingway at the Carnegie Institution of Science, who led the study. Image via Carnegie Science.

The fissures and water vapor plumes are of great interest to scientists, since they contain salty water from the subsurface ocean. NASA’s Cassini spacecraft was able to fly right through some of the plumes and sample them. It found water vapor, ice crystals, salts, methane and a variety of organic compounds. Cassini wasn’t equipped to detect if there was any life in the plumes, but it did confirm that the ocean is likely habitable by earthly standards. It even found evidence of hydrothermal vents on the ocean floor, thought to be similar to ones in Earth’s oceans. On Earth, they serve as oases for a wide range of microscopic and other life. As Hemingway concluded:

Since it is thanks to these fissures that we have been able to sample and study Enceladus’ subsurface ocean, which is beloved by astrobiologists, we thought it was important to understand the forces that formed and sustained them. Our modeling of the physical effects experienced by the moon’s icy shell points to a potentially unique sequence of events and processes that could allow for these distinctive stripes to exist.

Bottom line: A new study from the Carnegie Institution for Science is helping to explain how the unique tiger stripes on Saturn’s moon Enceladus formed.

Source: Cascading parallel fractures on Enceladus

Via Carnegie Science

from EarthSky https://ift.tt/2LLHRox

View of Saturn’s moon Enceladus via the Cassini spacecraft. You can see the bluish tiger stripes on the moon’s left side. This image is tilted; the tiger stripes are at the moon’s south pole. Active geysers are erupting from the stripes even as we speak! Image via NASA/ ESA/ JPL/ SSI/ Cassini Imaging Team/ Carnegie Science.

Saturn’s moon Enceladus is one of the most fascinating worlds in our solar system. It has a subsurface water ocean and huge geyser-like plumes of vapor. The geysers erupt at the moon’s south pole through large cracks in Enceladus’ icy crust. These fissures – known to scientists as tiger stripes – have been one of the most distinctive and puzzling features of the moon since the Cassini spacecraft first spied them in 2005. Scientists have wanted to know … how did the tiger stripes form? Why are they parallel? And why are they so evenly spaced? Now they think they have some answers.

A new peer-reviewed study from the Carnegie Institution for Science, published in Nature Astronomy on December 9, 2019, is helping to explain the weird physics behind Enceladus’ curious tiger stripes. The findings were announced by Carnegie Science on the same day.

In a statement about the results, lead author Doug Hemingway said:

First seen by the Cassini mission to Saturn, these stripes are like nothing else known in our solar system. They are parallel and evenly spaced, about 130 kilometers long and 35 kilometers apart [about 80 miles and 20 miles apart]. What makes them especially interesting is that they are continually erupting with water ice, even as we speak. No other icy planets or moons have anything quite like them.

EarthSky 2020 lunar calendars are available! They make great gifts. Order now. Going fast!

A closer view of the mysterious tiger stripes on Enceladus. Image via NASA/ ESA/ JPL/ SSI/ Cassini Imaging Team/ Gizmodo.

Along with Max Rudolph of the University of California, Davis and Michael Manga of UC Berkeley, Hemingway used computer models to try to determine how the stripes form and how they remain in place for so long.

The study addressed questions regarding two odd features of the stripes in particular: why they are only located at the south pole of Enceladus and why they are as parallel and evenly spaced as they are.

As to the first question, the researchers found that the stripes could probably have formed at either the south or north pole. This could have occurred at either pole first, it just happened to be the south pole in this case.

Enceladus’ ice crust is thinnest over the poles, so it makes sense that this is where such cracks would tend to develop. This is due to the fact that the poles experience the greatest amount of deformation caused by Saturn’s powerful gravitational pull. When the water below the ice partially freezes during periods of gradual cooling, the ice crust will thicken from below. This causes pressure to increase until the ice splits open, creating a fissure, or stripe.

Illustration depicting the interior of Enceladus. Water from the subsurface ocean percolates to the surface through cracks in the ice at the south pole, erupting in huge plumes. Image via NASA/ JPL-Caltech.

The geysers of Saturn’s moon Enceladus. These huge plumes of water vapor erupt through cracks at Enceladus’ south pole. The Cassini spacecraft analyzed the plumes and found they contain water vapor, ice particles, salts, methane and a variety of complex organic molecules. Scientists believe they originate from an ocean below the moon’s icy crust. Image via NASA/ JPL-Caltech/ Space Science Institute.

The repeated deformation, or stretching of the crust, creates internal heat and keeps Enceladus’ ocean from completely freezing.

But why are the stripes parallel and equally spaced apart? The new study answers that question, Rudolph said:

Our model explains the regular spacing of the cracks.

The researchers think that the fissure called Baghdad Sulcus formed first. It remained open instead of freezing shut again, which allowed ocean water to spew out from the crevasse. Ice and snow – from jets of water that erupted from the ocean below and then froze and fell back down on the surface – had built up along the edges of the Baghdad Sulcus fissure, the weight of which created additional fissures. Rudolph said:

That caused the ice sheet to flex just enough to set off a parallel crack about 35 km away.

The same gravitational tidal effects that helps create the stripes also keeps them open. The fissures are like open wounds in Enceladus’ crust that never heal. The cracks repeatedly widen and narrow again, flushing water out in the process.

This is also partly thanks to Enceladus’ small size; if the noon was significantly larger, its gravity would prevent the fissures from re-opening.

Doug Hemingway at the Carnegie Institution of Science, who led the study. Image via Carnegie Science.

The fissures and water vapor plumes are of great interest to scientists, since they contain salty water from the subsurface ocean. NASA’s Cassini spacecraft was able to fly right through some of the plumes and sample them. It found water vapor, ice crystals, salts, methane and a variety of organic compounds. Cassini wasn’t equipped to detect if there was any life in the plumes, but it did confirm that the ocean is likely habitable by earthly standards. It even found evidence of hydrothermal vents on the ocean floor, thought to be similar to ones in Earth’s oceans. On Earth, they serve as oases for a wide range of microscopic and other life. As Hemingway concluded:

Since it is thanks to these fissures that we have been able to sample and study Enceladus’ subsurface ocean, which is beloved by astrobiologists, we thought it was important to understand the forces that formed and sustained them. Our modeling of the physical effects experienced by the moon’s icy shell points to a potentially unique sequence of events and processes that could allow for these distinctive stripes to exist.

Bottom line: A new study from the Carnegie Institution for Science is helping to explain how the unique tiger stripes on Saturn’s moon Enceladus formed.

Source: Cascading parallel fractures on Enceladus

Via Carnegie Science

from EarthSky https://ift.tt/2LLHRox