cassini finale sept 15 2017 how to follow online

Artist’s concept of Cassini’s final plunge into Saturn.

NASA’s Cassini spacecraft is on final approach to Saturn, following confirmation by mission navigators that it is on course to dive into the planet’s atmosphere on Friday, September 15, 2017.

Cassini is ending its 13-year tour of the Saturn system with an intentional plunge into the planet to ensure Saturn’s moons – in particular Enceladus, with its subsurface ocean and signs of hydrothermal activity – remain pristine for future exploration. The spacecraft’s fateful dive is the final beat in the mission’s Grand Finale, 22 weekly dives, which began in late April, through the gap between Saturn and its rings. No spacecraft has ever ventured so close to the planet before. The mission’s final calculations predict loss of contact with the Cassini spacecraft will take place on September 15 at 7:55 a.m. EDT (11:55 UTC; translate to your time zone). Cassini will enter Saturn’s atmosphere approximately one minute earlier, at an altitude of about 1,190 miles (1,915 km) above the planet’s estimated cloud tops (the altitude where the air pressure is 1-bar, equivalent to sea level on Earth).

For the next couple of days, as Saturn looms ever larger, Cassini expects to take a last look around the Saturn system, snapping a few final images of the planet, features in its rings, and the moons Enceladus and Titan. The final set of views from Cassini’s imaging cameras is scheduled to be taken and transmitted to Earth on Thursday, September 14. If all goes as planned, images will be posted to the Cassini mission website beginning around 11 p.m. EDT (03:00 UTC on September 15). The unprocessed images will be available at:

http://ift.tt/2nALlPF

Live mission commentary and video from JPL Mission Control will air on NASA Television from 7 to 8:30 a.m. EDT (11 to 12:30 UTC; translate to your time zone) on September 15. A post-mission news briefing from JPL is currently scheduled for 9:30 a.m. EDT (13:30 UTC), also on NASA TV.

Click here to go to NASA TV

A new NASA e-book, The Saturn System Through the Eyes of Cassini, showcasing compelling images and key science discoveries from the mission, is available here, for free download, in multiple formats.

An online toolkit of information and resources about Cassini’s Grand Finale and final plunge into Saturn is available here.

Follow the Cassini spacecraft’s plunge on social media using #GrandFinale, or visit:

https://twitter.com/CassiniSaturn

http://ift.tt/2wKNIDC

During its dive into the atmosphere, the spacecraft’s speed will be approximately 70,000 miles (113,000 km) per hour. The final plunge will take place on the day side of Saturn, near local noon, with the spacecraft entering the atmosphere around 10 degrees north latitude.

When Cassini first begins to encounter Saturn’s atmosphere, the spacecraft’s attitude control thrusters will begin firing in short bursts to work against the thin gas and keep Cassini’s saucer-shaped high-gain antenna pointed at Earth to relay the mission’s precious final data. As the atmosphere thickens, the thrusters will be forced to ramp up their activity, going from 10 percent of their capacity to 100 percent in the span of about a minute. Once they are firing at full capacity, the thrusters can do no more to keep Cassini stably pointed, and the spacecraft will begin to tumble.

When the antenna points just a few fractions of a degree away from Earth, communications will be severed permanently. The predicted altitude for loss of signal is approximately 930 miles (1,500 kilometers) above Saturn’s cloud tops. From that point, the spacecraft will begin to burn up like a meteor. Within about 30 seconds following loss of signal, the spacecraft will begin to come apart; within a couple of minutes, all remnants of the spacecraft are expected to be completely consumed in the atmosphere of Saturn.

Due to the travel time for radio signals from Saturn, which changes as both Earth and the ringed planet travel around the Sun, events currently take place there 86 minutes before they are observed on Earth. This means that, although the spacecraft will begin to tumble and go out of communication at 6:31 a.m. EDT (3:31 a.m. PDT) at Saturn, the signal from that event will not be received at Earth until 86 minutes later.

Earl Maize, Cassini project manager at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California, said:

The spacecraft’s final signal will be like an echo. It will radiate across the solar system for nearly an hour and a half after Cassini itself has gone. Even though we’ll know that, at Saturn, Cassini has already met its fate, its mission isn’t truly over for us on Earth as long as we’re still receiving its signal.

Cassini’s last transmissions will be received by antennas at NASA’s Deep Space Network complex in Canberra, Australia.

Cassini is set to make groundbreaking scientific observations of Saturn, using eight of its 12 science instruments. All of the mission’s magnetosphere and plasma science instruments, plus the spacecraft’s radio science system, and its infrared and ultraviolet spectrometers will collect data during the final plunge.

Chief among the observations being made as Cassini dives into Saturn are those of the Ion and Neutral Mass Spectrometer (INMS). The instrument will directly sample the composition and structure of the atmosphere, which cannot be done from orbit. The spacecraft will be oriented so that INMS is pointed in the direction of motion, to allow it the best possible access to oncoming atmospheric gases.

Bottom line: Click here for links to the last few raw images gathered by Cassini prior to its plunge into Saturn on September 15, 2017, and to learn how to follow the mission’s end online.

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

Artist’s concept of Cassini’s final plunge into Saturn.

NASA’s Cassini spacecraft is on final approach to Saturn, following confirmation by mission navigators that it is on course to dive into the planet’s atmosphere on Friday, September 15, 2017.

Cassini is ending its 13-year tour of the Saturn system with an intentional plunge into the planet to ensure Saturn’s moons – in particular Enceladus, with its subsurface ocean and signs of hydrothermal activity – remain pristine for future exploration. The spacecraft’s fateful dive is the final beat in the mission’s Grand Finale, 22 weekly dives, which began in late April, through the gap between Saturn and its rings. No spacecraft has ever ventured so close to the planet before. The mission’s final calculations predict loss of contact with the Cassini spacecraft will take place on September 15 at 7:55 a.m. EDT (11:55 UTC; translate to your time zone). Cassini will enter Saturn’s atmosphere approximately one minute earlier, at an altitude of about 1,190 miles (1,915 km) above the planet’s estimated cloud tops (the altitude where the air pressure is 1-bar, equivalent to sea level on Earth).

For the next couple of days, as Saturn looms ever larger, Cassini expects to take a last look around the Saturn system, snapping a few final images of the planet, features in its rings, and the moons Enceladus and Titan. The final set of views from Cassini’s imaging cameras is scheduled to be taken and transmitted to Earth on Thursday, September 14. If all goes as planned, images will be posted to the Cassini mission website beginning around 11 p.m. EDT (03:00 UTC on September 15). The unprocessed images will be available at:

http://ift.tt/2nALlPF

Live mission commentary and video from JPL Mission Control will air on NASA Television from 7 to 8:30 a.m. EDT (11 to 12:30 UTC; translate to your time zone) on September 15. A post-mission news briefing from JPL is currently scheduled for 9:30 a.m. EDT (13:30 UTC), also on NASA TV.

Click here to go to NASA TV

A new NASA e-book, The Saturn System Through the Eyes of Cassini, showcasing compelling images and key science discoveries from the mission, is available here, for free download, in multiple formats.

An online toolkit of information and resources about Cassini’s Grand Finale and final plunge into Saturn is available here.

Follow the Cassini spacecraft’s plunge on social media using #GrandFinale, or visit:

https://twitter.com/CassiniSaturn

http://ift.tt/2wKNIDC

During its dive into the atmosphere, the spacecraft’s speed will be approximately 70,000 miles (113,000 km) per hour. The final plunge will take place on the day side of Saturn, near local noon, with the spacecraft entering the atmosphere around 10 degrees north latitude.

When Cassini first begins to encounter Saturn’s atmosphere, the spacecraft’s attitude control thrusters will begin firing in short bursts to work against the thin gas and keep Cassini’s saucer-shaped high-gain antenna pointed at Earth to relay the mission’s precious final data. As the atmosphere thickens, the thrusters will be forced to ramp up their activity, going from 10 percent of their capacity to 100 percent in the span of about a minute. Once they are firing at full capacity, the thrusters can do no more to keep Cassini stably pointed, and the spacecraft will begin to tumble.

When the antenna points just a few fractions of a degree away from Earth, communications will be severed permanently. The predicted altitude for loss of signal is approximately 930 miles (1,500 kilometers) above Saturn’s cloud tops. From that point, the spacecraft will begin to burn up like a meteor. Within about 30 seconds following loss of signal, the spacecraft will begin to come apart; within a couple of minutes, all remnants of the spacecraft are expected to be completely consumed in the atmosphere of Saturn.

Due to the travel time for radio signals from Saturn, which changes as both Earth and the ringed planet travel around the Sun, events currently take place there 86 minutes before they are observed on Earth. This means that, although the spacecraft will begin to tumble and go out of communication at 6:31 a.m. EDT (3:31 a.m. PDT) at Saturn, the signal from that event will not be received at Earth until 86 minutes later.

Earl Maize, Cassini project manager at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California, said:

The spacecraft’s final signal will be like an echo. It will radiate across the solar system for nearly an hour and a half after Cassini itself has gone. Even though we’ll know that, at Saturn, Cassini has already met its fate, its mission isn’t truly over for us on Earth as long as we’re still receiving its signal.

Cassini’s last transmissions will be received by antennas at NASA’s Deep Space Network complex in Canberra, Australia.

Cassini is set to make groundbreaking scientific observations of Saturn, using eight of its 12 science instruments. All of the mission’s magnetosphere and plasma science instruments, plus the spacecraft’s radio science system, and its infrared and ultraviolet spectrometers will collect data during the final plunge.

Chief among the observations being made as Cassini dives into Saturn are those of the Ion and Neutral Mass Spectrometer (INMS). The instrument will directly sample the composition and structure of the atmosphere, which cannot be done from orbit. The spacecraft will be oriented so that INMS is pointed in the direction of motion, to allow it the best possible access to oncoming atmospheric gases.

Bottom line: Click here for links to the last few raw images gathered by Cassini prior to its plunge into Saturn on September 15, 2017, and to learn how to follow the mission’s end online.

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

Irma turns Caribbean islands brown

The British and U.S. Virgin Islands, before and after Hurricane Irma (The white spots are clouds.) Image via NASA Earth Observatory.

By Kathryn Hansen/NASA Earth Observatory

Hurricane Irma churned across the Atlantic Ocean in September 2017, battering several Caribbean islands before moving on to the Florida Keys and the U.S. mainland. As the clouds cleared over places like the Virgin Islands, the destruction became obvious even from space.

These natural-color images, captured by the Operational Land Imager (OLI) on the Landsat 8 satellite, show some of Irma’s effect on the British and U.S. Virgin Islands. The views were acquired on August 25 and September 10, 2017, before and after the storm passed. They are among the few relatively cloud-free satellite images of the area so far.

The most obvious change is the widespread browning of the landscape. There are a number of possible reasons for this. Lush green tropical vegetation can be ripped away by a storm’s strong winds, leaving the satellite with a view of more bare ground. Also, salt spray whipped up by the hurricane can coat and desiccate leaves while they are still on the trees.

Irma passed the northernmost Virgin Islands on the afternoon of September 6. At the time, Irma was a category 5 storm with maximum sustained winds of 185 miles (295 kilometers) per hour. According to news reports, the islands saw “significant devastation.”

A close-up of Virgin Gorda gives a better sense of the changes. Note how some of the vegetation on the south and west of the island is a bit greener, likely because it was partly shielded from winds by the hills in the center. Differences in ocean color likely stem from differences in the ocean surface; rougher surfaces scatter more light, and appear brighter and lighter. Image via NASA Earth Observatory.

The destruction is also clearly visible on Barbuda. This small island in the eastern Caribbean was directly hit by the category-5 storm early on September 6, 2017. The left image shows Barbuda on August 21. The right image shows the ravaged landscape on September 8. In contrast, vegetation on Antigua appears relatively healthy and intact. With the storm’s center passing to the north, the island sustained less damage. Ground reports noted that by September 7, electricity had been restored to most of the island, and the international airport reopened. Image via NASA Earth Observatory.

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The British and U.S. Virgin Islands, before and after Hurricane Irma (The white spots are clouds.) Image via NASA Earth Observatory.

By Kathryn Hansen/NASA Earth Observatory

Hurricane Irma churned across the Atlantic Ocean in September 2017, battering several Caribbean islands before moving on to the Florida Keys and the U.S. mainland. As the clouds cleared over places like the Virgin Islands, the destruction became obvious even from space.

These natural-color images, captured by the Operational Land Imager (OLI) on the Landsat 8 satellite, show some of Irma’s effect on the British and U.S. Virgin Islands. The views were acquired on August 25 and September 10, 2017, before and after the storm passed. They are among the few relatively cloud-free satellite images of the area so far.

The most obvious change is the widespread browning of the landscape. There are a number of possible reasons for this. Lush green tropical vegetation can be ripped away by a storm’s strong winds, leaving the satellite with a view of more bare ground. Also, salt spray whipped up by the hurricane can coat and desiccate leaves while they are still on the trees.

Irma passed the northernmost Virgin Islands on the afternoon of September 6. At the time, Irma was a category 5 storm with maximum sustained winds of 185 miles (295 kilometers) per hour. According to news reports, the islands saw “significant devastation.”

A close-up of Virgin Gorda gives a better sense of the changes. Note how some of the vegetation on the south and west of the island is a bit greener, likely because it was partly shielded from winds by the hills in the center. Differences in ocean color likely stem from differences in the ocean surface; rougher surfaces scatter more light, and appear brighter and lighter. Image via NASA Earth Observatory.

The destruction is also clearly visible on Barbuda. This small island in the eastern Caribbean was directly hit by the category-5 storm early on September 6, 2017. The left image shows Barbuda on August 21. The right image shows the ravaged landscape on September 8. In contrast, vegetation on Antigua appears relatively healthy and intact. With the storm’s center passing to the north, the island sustained less damage. Ground reports noted that by September 7, electricity had been restored to most of the island, and the international airport reopened. Image via NASA Earth Observatory.

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Donate to EarthSky: Your support means the world to us

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Things That Go Boom? Take Batteries Off The List

Army and university researchers have developed a battery that uses a water-salt solution as its electrolyte and reaches the 4.0 volt mark desired for household electronics, such as laptop computers, without the fire and explosive risks associated with some batteries.

from http://ift.tt/2y5Co35

Army and university researchers have developed a battery that uses a water-salt solution as its electrolyte and reaches the 4.0 volt mark desired for household electronics, such as laptop computers, without the fire and explosive risks associated with some batteries.

from http://ift.tt/2y5Co35

Andromeda galaxy: Milky Way’s next-door neighbor

Josh Blash captured this image of the Andromeda galaxy.

Although a couple of dozen minor galaxies lie closer to our Milky Way, the Andromeda galaxy is the closest major galaxy to ours. Excluding the Large and Small Magellanic Clouds, which can’t be seen from northerly latitudes, the Andromeda galaxy – also known as M31 – is the brightest galaxy in all the heavens. It’s the most distant thing you can see with your unaided eye, at 2.3 million light-years. To the eye, it appears as a smudge of light larger than a full moon. Follow the links below to learn more about the Andromeda galaxy.

When to look for the Andromeda Galaxy

Find the Andromeda galaxy using the Great Square of Pegasus

Find the Andromeda galaxy using the constellation Cassiopeia

History of our knowledge of the Andromeda galaxy

Andromeda and Milky Way in context

Earthsky friend Thomas Wildoner, caught the Andromeda galaxy in August 2014.

When to look for the Andromeda Galaxy. From mid-northern latitudes, you can see M31 – also called the Andromeda galaxy – for at least part of every night, all year long. But most people see the galaxy first in northern autumn, when it’s high enough in the sky to be seen from nightfall till daybreak.

In late September and early October, the Andromeda galaxy shines in your eastern sky at nightfall, swings high overhead around midnight (1 a.m. daylight saving time) and stands rather high in the west at the onset of morning dawn. Winter evenings are also good for viewing the Andromeda galaxy.

If you are far from city lights, and it’s a moonless night – and you’re looking on an autumn or winter evening – it’s possible you’ll simply notice the galaxy in your night sky. It’s looks like a hazy patch in the sky, as wide across as a full moon.

But if you look, and don’t see the galaxy – yet you know you’re looking at a time when it’s above the horizon – you can star-hop to find the galaxy in one of two ways. First, you can use the Great Square of Pegasus. Second, you can use the constellation Cassiopeia.

Use the Great Square of Pegasus to find the Andromeda Galaxy. A line between Mirach and Mu Andromedae points to the galaxy.

Find the Andromeda galaxy using the Great Square of Pegasus. You’ll be hopping to the Andromeda galaxy from the Great Square of Pegasus. In autumn, the Great Square of Pegasus looks like a great big baseball diamond in the eastern sky. Envision the bottom star of the Square’s four stars as home plate, then draw an imaginary line from the “first base” star though the “third base” star to locate two streamers of stars flying away from the Great Square. These stars belong to the constellation Andromeda the Princess.

On each streamer, go two stars north (left) of the third base star, locating the stars Mirach and Mu Andromedae. Draw a line from Mirach through Mu Andromedae, going twice the Mirach/Mu Andromedae distance. You’ve just landed on the Andromeda galaxy, which looks like a smudge of light to the unaided eye.

If you can’t see the Andromeda galaxy with the eye alone, by all means use binoculars.

Many people use the M- or W-shaped constellation Cassiopeia to find the Andromeda galaxy. See how the star Schedar points to the galaxy?

Find the Andromeda galaxy using the constellation Cassiopeia. The constellation Cassiopeia the Queen is one of the easiest constellations to recognize. It is shaped like the letter M or W. Look generally northward on the sky’s dome to find this constellation. If you can recognize the north star, Polaris – and if you know how to find the Big Dipper – be aware that the Big Dipper and Cassiopeia move around Polaris like the hands of a clock, always opposite each other.

To find the Andromeda galaxy via Cassiopeia, look for the star Schedar. In the illustration above, see how the star Schedar points to the galaxy?

Many people use the Cassiopeia to find the Andromeda galaxy, because Cassiopeia itself is so easy to spot.

The Great Andromeda Nebula, photographed in the year 1900. At this point, astronomers could not discern individual stars in the galaxy. Many thought it was a cloud of gas within our Milky Way – a place where new stars were forming. Image via Wikimedia Commons.

History of our knowledge of the Andromeda galaxy. At one time, the Andromeda galaxy was called the Great Andromeda Nebula. Astronomers thought this patch of light was composed of glowing gases, or was perhaps a solar system in the process of formation.

It wasn’t until the 20th century that astronomers were able to resolve the Andromeda spiral nebula into individual stars. This discovery lead to a controversy about whether the Andromeda spiral nebula and other spiral nebulae lie within or outside the Milky Way.

In the 1920s Edwin Hubble finally put the matter to rest, when he used Cepheid variable stars within the Andromeda galaxy to determine that it is indeed an island universe residing beyond the bounds of our Milky Way galaxy.

Artist’s illustration of our Local Group via Chandra X-Ray Observatory.

Andromeda and Milky Way in context. The Andromeda galaxy and our Milky Way galaxy reign as the two most massive and dominant galaxies within the Local Group of Galaxies. The Andromeda Galaxy is the largest galaxy of the Local Group, which, in addition to the Milky Way, also contains the Triangulum Galaxy, and about 30 other smaller galaxies.

Both the Milky Way and the Andromeda galaxies lay claim to about a dozen satellite galaxies. Both are some 100,000 light-years across, containing enough mass to make billions of stars.

Astronomers have discovered that our Local Group is on the outskirts of a giant cluster of several thousand galaxies – which astronomers call the Virgo Cluster.

We also know of an irregular supercluster of galaxies, which contains the Virgo Cluster, which in turn contains our Local Group, which in turn contains our Milky Way galaxy and the nearby and Andromeda galaxy. At least 100 galaxy groups and clusters are located within this Virgo Supercluster. Its diameter is thought to be about 110 million light-years.

The Virgo Supercluster is thought to be one of millions of superclusters in the observable universe.

The Andromeda Galaxy with two of its satellite galaxies, via Wikimedia Commons. Click here to expand.

Bottom line: At 2.3 million light-years, the Great Andromeda galaxy (Messier 31) rates as one of the most distant objects you can see with the unaided eye.

The Andromeda galaxy (M31) is at RA: 0h 42.7m; Dec: 41^o 16′ north

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Josh Blash captured this image of the Andromeda galaxy.

Although a couple of dozen minor galaxies lie closer to our Milky Way, the Andromeda galaxy is the closest major galaxy to ours. Excluding the Large and Small Magellanic Clouds, which can’t be seen from northerly latitudes, the Andromeda galaxy – also known as M31 – is the brightest galaxy in all the heavens. It’s the most distant thing you can see with your unaided eye, at 2.3 million light-years. To the eye, it appears as a smudge of light larger than a full moon. Follow the links below to learn more about the Andromeda galaxy.

When to look for the Andromeda Galaxy

Find the Andromeda galaxy using the Great Square of Pegasus

Find the Andromeda galaxy using the constellation Cassiopeia

History of our knowledge of the Andromeda galaxy

Andromeda and Milky Way in context

Earthsky friend Thomas Wildoner, caught the Andromeda galaxy in August 2014.

When to look for the Andromeda Galaxy. From mid-northern latitudes, you can see M31 – also called the Andromeda galaxy – for at least part of every night, all year long. But most people see the galaxy first in northern autumn, when it’s high enough in the sky to be seen from nightfall till daybreak.

In late September and early October, the Andromeda galaxy shines in your eastern sky at nightfall, swings high overhead around midnight (1 a.m. daylight saving time) and stands rather high in the west at the onset of morning dawn. Winter evenings are also good for viewing the Andromeda galaxy.

If you are far from city lights, and it’s a moonless night – and you’re looking on an autumn or winter evening – it’s possible you’ll simply notice the galaxy in your night sky. It’s looks like a hazy patch in the sky, as wide across as a full moon.

But if you look, and don’t see the galaxy – yet you know you’re looking at a time when it’s above the horizon – you can star-hop to find the galaxy in one of two ways. First, you can use the Great Square of Pegasus. Second, you can use the constellation Cassiopeia.

Use the Great Square of Pegasus to find the Andromeda Galaxy. A line between Mirach and Mu Andromedae points to the galaxy.

Find the Andromeda galaxy using the Great Square of Pegasus. You’ll be hopping to the Andromeda galaxy from the Great Square of Pegasus. In autumn, the Great Square of Pegasus looks like a great big baseball diamond in the eastern sky. Envision the bottom star of the Square’s four stars as home plate, then draw an imaginary line from the “first base” star though the “third base” star to locate two streamers of stars flying away from the Great Square. These stars belong to the constellation Andromeda the Princess.

On each streamer, go two stars north (left) of the third base star, locating the stars Mirach and Mu Andromedae. Draw a line from Mirach through Mu Andromedae, going twice the Mirach/Mu Andromedae distance. You’ve just landed on the Andromeda galaxy, which looks like a smudge of light to the unaided eye.

If you can’t see the Andromeda galaxy with the eye alone, by all means use binoculars.

Many people use the M- or W-shaped constellation Cassiopeia to find the Andromeda galaxy. See how the star Schedar points to the galaxy?

Find the Andromeda galaxy using the constellation Cassiopeia. The constellation Cassiopeia the Queen is one of the easiest constellations to recognize. It is shaped like the letter M or W. Look generally northward on the sky’s dome to find this constellation. If you can recognize the north star, Polaris – and if you know how to find the Big Dipper – be aware that the Big Dipper and Cassiopeia move around Polaris like the hands of a clock, always opposite each other.

To find the Andromeda galaxy via Cassiopeia, look for the star Schedar. In the illustration above, see how the star Schedar points to the galaxy?

Many people use the Cassiopeia to find the Andromeda galaxy, because Cassiopeia itself is so easy to spot.

The Great Andromeda Nebula, photographed in the year 1900. At this point, astronomers could not discern individual stars in the galaxy. Many thought it was a cloud of gas within our Milky Way – a place where new stars were forming. Image via Wikimedia Commons.

History of our knowledge of the Andromeda galaxy. At one time, the Andromeda galaxy was called the Great Andromeda Nebula. Astronomers thought this patch of light was composed of glowing gases, or was perhaps a solar system in the process of formation.

It wasn’t until the 20th century that astronomers were able to resolve the Andromeda spiral nebula into individual stars. This discovery lead to a controversy about whether the Andromeda spiral nebula and other spiral nebulae lie within or outside the Milky Way.

In the 1920s Edwin Hubble finally put the matter to rest, when he used Cepheid variable stars within the Andromeda galaxy to determine that it is indeed an island universe residing beyond the bounds of our Milky Way galaxy.

Artist’s illustration of our Local Group via Chandra X-Ray Observatory.

Andromeda and Milky Way in context. The Andromeda galaxy and our Milky Way galaxy reign as the two most massive and dominant galaxies within the Local Group of Galaxies. The Andromeda Galaxy is the largest galaxy of the Local Group, which, in addition to the Milky Way, also contains the Triangulum Galaxy, and about 30 other smaller galaxies.

Both the Milky Way and the Andromeda galaxies lay claim to about a dozen satellite galaxies. Both are some 100,000 light-years across, containing enough mass to make billions of stars.

Astronomers have discovered that our Local Group is on the outskirts of a giant cluster of several thousand galaxies – which astronomers call the Virgo Cluster.

We also know of an irregular supercluster of galaxies, which contains the Virgo Cluster, which in turn contains our Local Group, which in turn contains our Milky Way galaxy and the nearby and Andromeda galaxy. At least 100 galaxy groups and clusters are located within this Virgo Supercluster. Its diameter is thought to be about 110 million light-years.

The Virgo Supercluster is thought to be one of millions of superclusters in the observable universe.

The Andromeda Galaxy with two of its satellite galaxies, via Wikimedia Commons. Click here to expand.

Bottom line: At 2.3 million light-years, the Great Andromeda galaxy (Messier 31) rates as one of the most distant objects you can see with the unaided eye.

The Andromeda galaxy (M31) is at RA: 0h 42.7m; Dec: 41^o 16′ north

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Openings in Antarctic sea ice influence global climate

A polynya, or opening in the sea ice, occurred in the Southern Ocean’s Weddell sea during the winters of 1974-76, triggering a series of climatic and oceanographic changes. This image shows the sea ice concentration averaged over three September months 1974-1976 during the Weddell Polynya, made with data from the NIMBUS-V satellite from the National Snow Ice Data Center. Image via University of Pennsylvania.

According to a new analysis of climate models by an international team of researchers, heat escaping from the ocean through em>polynyas – or openings in sea ice – influences sea and atmospheric temperatures and wind patterns around the globe – even rainfall around the tropics.

In 1974, satellite images revealed a 250,000 square kilometer (96,526 square mile) polynya in the Weddell Sea, south of South America, that persisted over three winters. Such expansive ice-free areas in the ocean surrounding Antarctica haven’t been seen – until a small polynya was observed last year.

The new study, published September 8, 2017 in the Journal of Climate reveals the significant global effects that these seemingly anomalous polynyas can have. Though this process is part of a natural pattern of climate variability, the researchers say that it has implications for how the global climate will respond to future anthropogenic warming.

Irina Marinov, of the University of Pennsylvania is study author. She said in a statement:

This small, isolated opening in the sea ice in the Southern Ocean can have significant, large-scale climate implications. Climate models suggest that, in years and decades with a large polynya, the entire atmosphere warms globally, and we see changes in the winds in the Southern Hemisphere and a southward shift in the equatorial rain belt. This is attributable to the polynya.

Typically, the Southern Ocean is covered in ice during the Southern Hemisphere’s winter. Polynyas occur when warm subsurface waters of North Atlantic and equatorial origin mix locally with cold surface waters.

Until recently, climate scientists and oceanographers believed that atmospheric and ocean conditions around the tropics were the primary drivers in affecting conditions outside the tropics. But in the last few years, scientists have shown that the opposite is also true: the Southern Ocean has an important role in affecting tropical and Northern Hemisphere climates.

When the polynyas occur- roughly every 75 years – they act as a release valve for the ocean’s heat, said the researchers. Not only does the immediate area warm, but there are also increases in overall sea-surface and atmospheric temperatures of the entire Southern Hemisphere and, to a lesser extent, the Northern Hemisphere. Changes in north-south temperature gradients lead to changes in wind patterns as well. Marinov said:

We are seeing a decrease in what we call the Southern Hemisphere westerlies and changes in trade winds. And these winds affect storms, precipitation and clouds.

Among these changes in precipitation is a shift in an equatorial belt where trade winds converge, resulting in intense precipitation. When a polynya occurs, this rain belt moves south a few degrees and stays there for 20 to 30 years before shifting back. Marinov said:

This affects water resources in, for example, Indonesia, South America and sub-Saharan Africa. We have a natural variation in climate that may be, among other effects, impacting agricultural production in heavily populated regions of the world.

Bottom line: Heat escaping through polynyas – openings in sea ice – influences sea and atmospheric temperatures and wind patterns around the globe, according to new study.

Read more from the University of Pennsylvania

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A polynya, or opening in the sea ice, occurred in the Southern Ocean’s Weddell sea during the winters of 1974-76, triggering a series of climatic and oceanographic changes. This image shows the sea ice concentration averaged over three September months 1974-1976 during the Weddell Polynya, made with data from the NIMBUS-V satellite from the National Snow Ice Data Center. Image via University of Pennsylvania.

According to a new analysis of climate models by an international team of researchers, heat escaping from the ocean through em>polynyas – or openings in sea ice – influences sea and atmospheric temperatures and wind patterns around the globe – even rainfall around the tropics.

In 1974, satellite images revealed a 250,000 square kilometer (96,526 square mile) polynya in the Weddell Sea, south of South America, that persisted over three winters. Such expansive ice-free areas in the ocean surrounding Antarctica haven’t been seen – until a small polynya was observed last year.

The new study, published September 8, 2017 in the Journal of Climate reveals the significant global effects that these seemingly anomalous polynyas can have. Though this process is part of a natural pattern of climate variability, the researchers say that it has implications for how the global climate will respond to future anthropogenic warming.

Irina Marinov, of the University of Pennsylvania is study author. She said in a statement:

This small, isolated opening in the sea ice in the Southern Ocean can have significant, large-scale climate implications. Climate models suggest that, in years and decades with a large polynya, the entire atmosphere warms globally, and we see changes in the winds in the Southern Hemisphere and a southward shift in the equatorial rain belt. This is attributable to the polynya.

Typically, the Southern Ocean is covered in ice during the Southern Hemisphere’s winter. Polynyas occur when warm subsurface waters of North Atlantic and equatorial origin mix locally with cold surface waters.

Until recently, climate scientists and oceanographers believed that atmospheric and ocean conditions around the tropics were the primary drivers in affecting conditions outside the tropics. But in the last few years, scientists have shown that the opposite is also true: the Southern Ocean has an important role in affecting tropical and Northern Hemisphere climates.

When the polynyas occur- roughly every 75 years – they act as a release valve for the ocean’s heat, said the researchers. Not only does the immediate area warm, but there are also increases in overall sea-surface and atmospheric temperatures of the entire Southern Hemisphere and, to a lesser extent, the Northern Hemisphere. Changes in north-south temperature gradients lead to changes in wind patterns as well. Marinov said:

We are seeing a decrease in what we call the Southern Hemisphere westerlies and changes in trade winds. And these winds affect storms, precipitation and clouds.

Among these changes in precipitation is a shift in an equatorial belt where trade winds converge, resulting in intense precipitation. When a polynya occurs, this rain belt moves south a few degrees and stays there for 20 to 30 years before shifting back. Marinov said:

This affects water resources in, for example, Indonesia, South America and sub-Saharan Africa. We have a natural variation in climate that may be, among other effects, impacting agricultural production in heavily populated regions of the world.

Bottom line: Heat escaping through polynyas – openings in sea ice – influences sea and atmospheric temperatures and wind patterns around the globe, according to new study.

Read more from the University of Pennsylvania

from EarthSky http://ift.tt/2wpj3rA

Does organic material in comets predate our solar system?

Comet 67P/Churyumov-Gerasimenko as seen by ESA’s Rosetta spacecraft.

On September 4, 2017, researchers in Paris announced the results of their study of the organic compounds – combinations of carbon, hydrogen, nitrogen, and oxygen – in comet 67P Churyumov-Gerasimenko. This is the comet studied up-close and in detail by ESA’s Rosetta spacecraft for two years, beginning in August 2014. The sorts of organic molecules found in this comet and others have long been proposed by scientists as possible building blocks for life on Earth. Published in late August in the peer-reviewed journal Monthly Notices of the Royal Astronomical Society, the French researchers advance the theory that this organic matter has its origin in interstellar space and predates the birth of our solar system.

The Rosetta mission found a large amount of organic material in the nucleus of the comet, which some people simply 67P and others call Chury for Klim Ivanovich Churyumov, one of its discovers. The Rosetta mission found that organic matter made up 40% (by mass) of the nucleus of the comet. According to researchers Jean-Loup Bertaux and Rosine Lallement, not only were the organic molecules were produced in interstellar space, well before the formation of the solar system, but also other astronomers are already very familiar with the source of this matter. Their statement explained:

For 70 years, scientists have known that analysis of stellar spectra indicates unknown absorptions, throughout interstellar space, at specific wavelengths called the diffuse interstellar bands (DIBs). DIBs are attributed to complex organic molecules that American astrophysicist Theodore Snow believes may constitute the largest known reservoir of organic matter in the universe.

This interstellar organic material is usually found in the same proportions. However, very dense clouds of matter like presolar nebulae are exceptions. In the middle of these nebulae, where matter is even denser, DIB absorptions plateau or even drop. This is because the organic molecules responsible for DIBs clump together there. The clumped matter absorbs less radiation than when it floated freely in space.

Such primitive nebulae end up contracting to form a solar system like our own, with planets . . . and comets. The Rosetta mission taught us that comet nuclei form by gentle accretion of grains progressively greater in size. First, small particles stick together to form larger grains. These in turn combine to form still larger chunks, and so on, until we have a comet nucleus a few kilometers wide.

Thus, the organic molecules that formerly populated the primitive nebulae—and that are responsible for DIBs—were probably not destroyed, but instead incorporated into the grains making up cometary nuclei. And there they have remained for 4.6 billion years. A sample-return mission would allow laboratory analysis of cometary organic material and finally reveal the identity of the mysterious interstellar matter underlying observed patterns in stellar spectra.

If cometary organic molecules were indeed produced in interstellar space—and if they played a role in the emergence of life on our planet, as scientists believe today—might they not also have seeded life on many other planets of our galaxy?

Artist’s concept of comets seeding the early Earth – or perhaps another planet – with organic material. Image via Mdosnewscienceworld.

Bottom line: French researchers advance the theory that the organic matter found in comets – possible building blocks for earthly life – has its origin in interstellar space and predates the birth of our solar system.

Via CNRS

from EarthSky http://ift.tt/2h0LN8h

Comet 67P/Churyumov-Gerasimenko as seen by ESA’s Rosetta spacecraft.

On September 4, 2017, researchers in Paris announced the results of their study of the organic compounds – combinations of carbon, hydrogen, nitrogen, and oxygen – in comet 67P Churyumov-Gerasimenko. This is the comet studied up-close and in detail by ESA’s Rosetta spacecraft for two years, beginning in August 2014. The sorts of organic molecules found in this comet and others have long been proposed by scientists as possible building blocks for life on Earth. Published in late August in the peer-reviewed journal Monthly Notices of the Royal Astronomical Society, the French researchers advance the theory that this organic matter has its origin in interstellar space and predates the birth of our solar system.

The Rosetta mission found a large amount of organic material in the nucleus of the comet, which some people simply 67P and others call Chury for Klim Ivanovich Churyumov, one of its discovers. The Rosetta mission found that organic matter made up 40% (by mass) of the nucleus of the comet. According to researchers Jean-Loup Bertaux and Rosine Lallement, not only were the organic molecules were produced in interstellar space, well before the formation of the solar system, but also other astronomers are already very familiar with the source of this matter. Their statement explained:

For 70 years, scientists have known that analysis of stellar spectra indicates unknown absorptions, throughout interstellar space, at specific wavelengths called the diffuse interstellar bands (DIBs). DIBs are attributed to complex organic molecules that American astrophysicist Theodore Snow believes may constitute the largest known reservoir of organic matter in the universe.

This interstellar organic material is usually found in the same proportions. However, very dense clouds of matter like presolar nebulae are exceptions. In the middle of these nebulae, where matter is even denser, DIB absorptions plateau or even drop. This is because the organic molecules responsible for DIBs clump together there. The clumped matter absorbs less radiation than when it floated freely in space.

Such primitive nebulae end up contracting to form a solar system like our own, with planets . . . and comets. The Rosetta mission taught us that comet nuclei form by gentle accretion of grains progressively greater in size. First, small particles stick together to form larger grains. These in turn combine to form still larger chunks, and so on, until we have a comet nucleus a few kilometers wide.

Thus, the organic molecules that formerly populated the primitive nebulae—and that are responsible for DIBs—were probably not destroyed, but instead incorporated into the grains making up cometary nuclei. And there they have remained for 4.6 billion years. A sample-return mission would allow laboratory analysis of cometary organic material and finally reveal the identity of the mysterious interstellar matter underlying observed patterns in stellar spectra.

If cometary organic molecules were indeed produced in interstellar space—and if they played a role in the emergence of life on our planet, as scientists believe today—might they not also have seeded life on many other planets of our galaxy?

Artist’s concept of comets seeding the early Earth – or perhaps another planet – with organic material. Image via Mdosnewscienceworld.

Bottom line: French researchers advance the theory that the organic matter found in comets – possible building blocks for earthly life – has its origin in interstellar space and predates the birth of our solar system.

Via CNRS

from EarthSky http://ift.tt/2h0LN8h

Farthest lunar perigee on September 13

Moon image via US Naval Observatory

The moon sweeps to perigee – its closest point to Earth in its monthly orbit – on September 13, 2017. Yet, at a distance of 369,860 km, this particular perigee counts as the most distant of this year’s 13 perigees. That’s in contrast to the year’s closest perigee of 357,207 km on May 26, 2017.

The moon swings to perigee and reaches its last quarter phase on September 13, 2017. One fortnight (two weeks) previous to the year’s farthest perigee, the moon had swung out to its closest apogee – farthest point from Earth in its monthly orbit – on August 30. It’s no accident that the year’s farthest perigee (close moon) and year’s closest apogee (far moon) happen in close vicinity of the quarter moons.

Lunar perigee and apogee calculator

Like everything else in nature, the moon’s orbit is always in flux. Its shape, and its orientation relative to the Earth and sun, change all the time. The complexities of the lunar orbit all combine to bring about today’s most distant lunar perigee of the year at 16:04 UTC (11:04 a.m. CDT; translate to your time zone).

If you’re game, we’ll share a secret with you. We’ll tell you why a quarter moon at perigee is farther than the mean perigee of 363,396 km, and why a quarter moon at apogee is closer than the mean apogee distance of 405,504 km. We’ll also explain why a full moon or new moon at perigee is closer than the mean perigee, yet why a full moon or new moon at apogee is farther than the mean apogee. It all has to do with the varying eccentricity of the moon’s orbit.

The moon’s eccentric orbit

The moon’s orbit around Earth, like the Earth’s orbit around the sun, is not a perfect circle. It’s a slightly oblong ellipse. That’s why, every month, the moon reaches a nearest point to Earth at perigee and a farthest point at apogee.

However, the moon’s orbit is not highly eccentric (oblong), but nearly circular, as shown on the illustration below.

The moon’s orbit around Earth is not a perfect circle. But it is very nearly circular, as the above diagram shows. Diagram by Brian Koberlein.

The illustrations above and below label perigee (moon’s closest point to Earth) and apogee (moon’s farthest point from Earth). A line drawn from perigee to apogee defines the major axis, or the longest diameter, of the moon’s elliptical orbit. In the parlance of astronomers, the perigee-to-apogee line is called the line of apsides. The center of the line of apsides to either the perigee point or apogee point is called the semi-major axis.

Image credit: NASA. The moon’s orbit is closer to being a circle than the diagram suggests, but the exaggeration helps to clarify. The moon is closest to Earth in its orbit at perigee and farthest away at apogee.

Earth does not lie at the center of the line of apsides. Instead, the Earth is offset from the center of the major axis, or line of apsides, toward the lunar perigee point. To be more precise, the Earth resides at one of the two foci of the ellipse.

Keep in mind, also, that the moon’s major axis (longest diameter of an ellipse) always makes a right angle to the moon’s minor axis (shortest diameter of an ellipse).

Varying eccentricity of the moon’s orbit

When the moon’s major axis, or line of apsides, makes a right angle to the sun-Earth line (B in below diagram), the moon’s eccentricity decreases to a minimum. In other words, the moon’s orbit is closest to being circular when the moon’s minor axis points toward the sun. Although the moon still swings closest to Earth at perigee and farthest from Earth at apogee, the perigee distance increases and the apogee distance decreases whenever the moon’s eccentricity lessens, or more closely approaches a circle in shape.

Image via Bedford Astronomy Club.

Therefore, in 2017, the moon’s minimal eccentricity ushers in the closest apogee of the year on August 30 (404,308 km), and the year’s farthest perigee one fortnight (two weeks) later, on September 13 (369,860 km). (See B in above diagram.)

Read more: Close and far moons in 2017

Some 103 days after the minor axis points sunward (B in above diagram), it’s then the moon’s major axis that points in the sun’s direction (C in above diagram). When the major axis, or line of apsides, aligns with the sun-Earth line, the eccentricity of the moon’s orbit increases to a maximum, and its orbit becomes maximally oblong. That causes the moon to swing extra-far from Earth at lunar apogee – yet extra-close to Earth at lunar perigee.

Therefore, the new moon of December 18, 2017, will closely align with the year’s most distant apogee (406,603 km). One fortnight (two weeks) after the farthest perigee in 2017, the full moon on January 2, 2018, will present the closest perigee of 2018 (356,565 km). (See C in the above diagram.)

Also, some 103 days before the minor axis points sunward (B in above diagram), the moon’s major axis also points in the sun’s direction (A in above diagram). Again, this causes the eccentricity of the moon’s orbit to increase, to bring about a closer perigee yet farther apogee.

So, in 2017, the new supermoon of May 25, 2017 (A in above diagram) closely coincided with the year’s nearest perigee (357,207 km). Then 7 lunar months (some 206 days) thereafter (C in above diagram), the new moon of December 18, 2017, will closely align with the year’s most distant apogee (406,603 km).

And 7 lunar months (206 days) after the year’s farthest full moon (micro moon) on June 9, 2017, it’ll be the closest full moon of 2018 on January 2, 2018.

Top: When the moon’s major axis (perigee-apogee line) points sunward, with perigee residing between the Earth and sun, the result is a new moon at perigee. Bottom: Some 206 days later, the moon’s major axis again aligns with the Earth and sun, but this time around, perigee is opposite the sun in Earth’s sky, giving rise to a full moon at perigee. Image and caption via NOAA.

Want to know more? Eclipses and the moon’s orbit

Resources:

Lunar perigee and apogee calculator

Moon at perigee and apogee: 2001 to 2100

Phases of the moon: 2001 to 2100

Bottom line: In 2017, the moon swings to its most distant perigee on September 13, 2017.

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

Moon image via US Naval Observatory

The moon sweeps to perigee – its closest point to Earth in its monthly orbit – on September 13, 2017. Yet, at a distance of 369,860 km, this particular perigee counts as the most distant of this year’s 13 perigees. That’s in contrast to the year’s closest perigee of 357,207 km on May 26, 2017.

The moon swings to perigee and reaches its last quarter phase on September 13, 2017. One fortnight (two weeks) previous to the year’s farthest perigee, the moon had swung out to its closest apogee – farthest point from Earth in its monthly orbit – on August 30. It’s no accident that the year’s farthest perigee (close moon) and year’s closest apogee (far moon) happen in close vicinity of the quarter moons.

Lunar perigee and apogee calculator

Like everything else in nature, the moon’s orbit is always in flux. Its shape, and its orientation relative to the Earth and sun, change all the time. The complexities of the lunar orbit all combine to bring about today’s most distant lunar perigee of the year at 16:04 UTC (11:04 a.m. CDT; translate to your time zone).

If you’re game, we’ll share a secret with you. We’ll tell you why a quarter moon at perigee is farther than the mean perigee of 363,396 km, and why a quarter moon at apogee is closer than the mean apogee distance of 405,504 km. We’ll also explain why a full moon or new moon at perigee is closer than the mean perigee, yet why a full moon or new moon at apogee is farther than the mean apogee. It all has to do with the varying eccentricity of the moon’s orbit.

The moon’s eccentric orbit

The moon’s orbit around Earth, like the Earth’s orbit around the sun, is not a perfect circle. It’s a slightly oblong ellipse. That’s why, every month, the moon reaches a nearest point to Earth at perigee and a farthest point at apogee.

However, the moon’s orbit is not highly eccentric (oblong), but nearly circular, as shown on the illustration below.

The moon’s orbit around Earth is not a perfect circle. But it is very nearly circular, as the above diagram shows. Diagram by Brian Koberlein.

The illustrations above and below label perigee (moon’s closest point to Earth) and apogee (moon’s farthest point from Earth). A line drawn from perigee to apogee defines the major axis, or the longest diameter, of the moon’s elliptical orbit. In the parlance of astronomers, the perigee-to-apogee line is called the line of apsides. The center of the line of apsides to either the perigee point or apogee point is called the semi-major axis.

Image credit: NASA. The moon’s orbit is closer to being a circle than the diagram suggests, but the exaggeration helps to clarify. The moon is closest to Earth in its orbit at perigee and farthest away at apogee.

Earth does not lie at the center of the line of apsides. Instead, the Earth is offset from the center of the major axis, or line of apsides, toward the lunar perigee point. To be more precise, the Earth resides at one of the two foci of the ellipse.

Keep in mind, also, that the moon’s major axis (longest diameter of an ellipse) always makes a right angle to the moon’s minor axis (shortest diameter of an ellipse).

Varying eccentricity of the moon’s orbit

When the moon’s major axis, or line of apsides, makes a right angle to the sun-Earth line (B in below diagram), the moon’s eccentricity decreases to a minimum. In other words, the moon’s orbit is closest to being circular when the moon’s minor axis points toward the sun. Although the moon still swings closest to Earth at perigee and farthest from Earth at apogee, the perigee distance increases and the apogee distance decreases whenever the moon’s eccentricity lessens, or more closely approaches a circle in shape.

Image via Bedford Astronomy Club.

Therefore, in 2017, the moon’s minimal eccentricity ushers in the closest apogee of the year on August 30 (404,308 km), and the year’s farthest perigee one fortnight (two weeks) later, on September 13 (369,860 km). (See B in above diagram.)

Read more: Close and far moons in 2017

Some 103 days after the minor axis points sunward (B in above diagram), it’s then the moon’s major axis that points in the sun’s direction (C in above diagram). When the major axis, or line of apsides, aligns with the sun-Earth line, the eccentricity of the moon’s orbit increases to a maximum, and its orbit becomes maximally oblong. That causes the moon to swing extra-far from Earth at lunar apogee – yet extra-close to Earth at lunar perigee.

Therefore, the new moon of December 18, 2017, will closely align with the year’s most distant apogee (406,603 km). One fortnight (two weeks) after the farthest perigee in 2017, the full moon on January 2, 2018, will present the closest perigee of 2018 (356,565 km). (See C in the above diagram.)

Also, some 103 days before the minor axis points sunward (B in above diagram), the moon’s major axis also points in the sun’s direction (A in above diagram). Again, this causes the eccentricity of the moon’s orbit to increase, to bring about a closer perigee yet farther apogee.

So, in 2017, the new supermoon of May 25, 2017 (A in above diagram) closely coincided with the year’s nearest perigee (357,207 km). Then 7 lunar months (some 206 days) thereafter (C in above diagram), the new moon of December 18, 2017, will closely align with the year’s most distant apogee (406,603 km).

And 7 lunar months (206 days) after the year’s farthest full moon (micro moon) on June 9, 2017, it’ll be the closest full moon of 2018 on January 2, 2018.

Top: When the moon’s major axis (perigee-apogee line) points sunward, with perigee residing between the Earth and sun, the result is a new moon at perigee. Bottom: Some 206 days later, the moon’s major axis again aligns with the Earth and sun, but this time around, perigee is opposite the sun in Earth’s sky, giving rise to a full moon at perigee. Image and caption via NOAA.

Want to know more? Eclipses and the moon’s orbit

Resources:

Lunar perigee and apogee calculator

Moon at perigee and apogee: 2001 to 2100

Phases of the moon: 2001 to 2100

Bottom line: In 2017, the moon swings to its most distant perigee on September 13, 2017.

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