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Astronomy Picture of the Day (APoD)
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Discover the cosmos!
Discover the cosmos!

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Tardigrade in Moss
Image Credit & Copyright: Nicole Ottawa & Oliver Meckes / Eye of Science / Science Source Images
https://apod.nasa.gov/apod/ap170326.html

Is this an alien? Probably not, but of all the animals on Earth, the tardigrade might be the best candidate. That's because tardigrades are known to be able to go for decades without food or water, to survive temperatures from near absolute zero to well above the boiling point of water, to survive pressures from near zero to well above that on ocean floors, and to survive direct exposure to dangerous radiations. The far-ranging survivability of these extremophiles was tested in 2011 outside an orbiting space shuttle. Tardigrades are so durable partly because they can repair their own DNA and reduce their body water content to a few percent. Some of these miniature water-bears almost became extraterrestrials recently when they were launched toward to the Martian moon Phobos on board the Russian mission Fobos-Grunt, but stayed terrestrial when a rocket failed and the capsule remained in Earth orbit. Tardigrades are more common than humans across most of the Earth. Pictured here in a color-enhanced electron micrograph, a millimeter-long tardigrade crawls on moss.
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Ganymede's Shadow
Image Credit & Copyright: Damian Peach, Chilescope
https://apod.nasa.gov/apod/ap170325.html

Approaching opposition early next month, Jupiter is offering some of its best telescopic views from planet Earth. On March 17, this impressively sharp image of the solar system's ruling gas giant was taken from a remote observatory in Chile. Bounded by planet girdling winds, familiar dark belts and light zones span the giant planet spotted with rotating oval storms. The solar system's largest moon Ganymede is above and left in the frame, its shadow seen in transit across the northern Jovian cloud tops. Ganymede itself is seen in remarkable detail along with bright surface features on fellow Galilean moon Io, right of Jupiter's looming disk.
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The Comet, the Owl, and the Galaxy
Image Credit & Copyright: Barry Riu
https://apod.nasa.gov/apod/ap170324.html

Comet 41P/Tuttle-Giacobini-Kresak poses for a Messier moment in this telescopic snapshot from March 21. In fact it shares the 1 degree wide field-of-view with two well-known entries in the 18th century comet-hunting astronomer's famous catalog. Sweeping through northern springtime skies just below the Big Dipper, the faint greenish comet was about 75 light-seconds from our fair planet. Dusty, edge-on spiral galaxy Messier 108 (bottom center) is more like 45 million light-years away. At upper right, the planetary nebula with an aging but intensely hot central star, the owlish Messier 97 is only about 12 thousand light-years distant though, still well within our own Milky Way galaxy. Named for its discoverer and re-discoverers, this faint periodic comet was first sighted in 1858 and not again until 1907 and 1951. Matching orbit calculations indicated that the same comet had been observed at widely separated times. Nearing its best apparition and closest approach to Earth in over 100 years on April 1, comet 41P orbits the Sun with a period of about 5.4 years.
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SH2-155: The Cave Nebula
Image Credit & Copyright: Eric Coles and Mel Helm
https://apod.nasa.gov/apod/ap170323.html

This skyscape features dusty Sharpless catalog emission region Sh2-155, the Cave Nebula. In the telescopic image, data taken through a narrowband filter tracks the reddish glow of ionized hydrogen atoms. About 2,400 light-years away, the scene lies along the plane of our Milky Way Galaxy toward the royal northern constellation of Cepheus. Astronomical explorations of the region reveal that it has formed at the boundary of the massive Cepheus B molecular cloud and the hot, young stars of the Cepheus OB 3 association. The bright rim of ionized hydrogen gas is energized by radiation from the hot stars, dominated by the brightest star above and left of picture center. Radiation driven ionization fronts are likely triggering collapsing cores and new star formation within. Appropriately sized for a stellar nursery, the cosmic cave is over 10 light-years across.
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Central Cygnus Skyscape
Image Credit & Copyright: Robert Gendler, DSS, BYU
https://apod.nasa.gov/apod/ap170322.html

In cosmic brush strokes of glowing hydrogen gas, this beautiful skyscape unfolds across the plane of our Milky Way Galaxy near the northern end of the Great Rift and the center of the constellation Cygnus the Swan. A 36 panel mosaic of telescopic image data, the scene spans about six degrees. Bright supergiant star Gamma Cygni (Sadr) to the upper left of the image center lies in the foreground of the complex gas and dust clouds and crowded star fields. Left of Gamma Cygni, shaped like two luminous wings divided by a long dark dust lane is IC 1318 whose popular name is understandably the Butterfly Nebula. The more compact, bright nebula at the lower right is NGC 6888, the Crescent Nebula. Some distance estimates for Gamma Cygni place it at around 1,800 light-years while estimates for IC 1318 and NGC 6888 range from 2,000 to 5,000 light-years.
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Fast Stars and Rogue Planets in the Orion Nebula
Image Credit: +NASA, +European Space Agency, ESA, Hubble
https://apod.nasa.gov/apod/ap170321.html

Start with the constellation of Orion. Below Orion's belt is a fuzzy area known as the Great Nebula of Orion. In this nebula is a bright star cluster known as the Trapezium, marked by four bright stars near the image center. The newly born stars in the Trapezium and surrounding regions show the Orion Nebula to be one of the most active areas of star formation to be found in our area of the Galaxy. In Orion, supernova explosions and close interactions between stars have created rogue planets and stars that rapidly move through space. Some of these fast stars have been found by comparing different images of this region taken by the Hubble Space Telescope many years apart. Many of the stars in the featured image, taken in visible and near-infrared light, appear unusually red because they are seen through dust that scatters away much of their blue light.
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The Aurora Tree
Image Credit & Copyright: Alyn Wallace Photography
https://apod.nasa.gov/apod/ap170320.html

Yes, but can your tree do this? Pictured is a visual coincidence between the dark branches of a nearby tree and bright glow of a distant aurora. The beauty of the aurora -- combined with how it seemed to mimic a tree right nearby -- mesmerized the photographer to such a degree that he momentarily forgot to take pictures. When viewed at the right angle, it seemed that this tree had aurora for leaves! Fortunately, before the aurora morphed into a different overall shape, he came to his senses and capture the awe-inspiring momentary coincidence. Typically triggered by solar explosions, aurora are caused by high energy electrons impacting the Earth's atmosphere around 150 kilometers up. The unusual Earth-sky collaboration was witnessed earlier this month in Iceland.
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Equinox on a Spinning Earth
Image Credit: +NASA, Meteosat, Robert Simmon
https://apod.nasa.gov/apod/ap170319.html

When does the line between day and night become vertical? Tomorrow. Tomorrow is an equinox on planet Earth, a time of year when day and night are most nearly equal. At an equinox, the Earth's terminator -- the dividing line between day and night -- becomes vertical and connects the north and south poles. The featured time-lapse video demonstrates this by displaying an entire year on planet Earth in twelve seconds. From geosynchronous orbit, the Meteosat satellite recorded these infrared images of the Earth every day at the same local time. The video started at the September 2010 equinox with the terminator line being vertical. As the Earth revolved around the Sun, the terminator was seen to tilt in a way that provides less daily sunlight to the northern hemisphere, causing winter in the north. As the year progressed, the March 2011 equinox arrived halfway through the video, followed by the terminator tilting the other way, causing winter in the southern hemisphere -- and summer in the north. The captured year ends again with the September equinox, concluding another of billions of trips the Earth has taken -- and will take -- around the Sun.
2017 March 19

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JWST: Ghosts and Mirrors
Image Credit: Chris Gunn, +NASA
https://apod.nasa.gov/apod/ap170318.html

Ghosts aren't actually hovering over the James Webb Space Telescope. But the lights are out as it stands with gold tinted mirror segments and support structures folded in Goddard Space Flight Center's Spacecraft Systems Development and Integration Facility clean room. Following vibration and acoustic testing, bright flashlights and ultraviolet lights are played over the stationary telescope looking for contamination, easier to spot in a darkened room. In the dimness the camera's long exposure creates the ghostly apparitions, blurring the moving lights and engineers. A scientific successor to Hubble, the James Webb Space Telescope is optimized for the infrared exploration of the early Universe. Its planned launch is in 2018 from French Guiana on a European Space Agency Ariane 5 rocket.
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Phases of Venus
Image Credit & Copyright: Daniel Herron
https://apod.nasa.gov/apod/ap170317.html

Just as the Moon goes through phases, Venus' visible sunlit hemisphere waxes and wanes. This composite of telescopic images illustrates the steady changes for the inner planet, seen in the west as the evening star, as Venus grows larger but narrows to a thin crescent from December 20, 2016 through March 10. Gliding along its interior orbit between Earth and Sun, Venus grows larger during that period because it is approaching planet Earth. Its crescent narrows, though, as Venus swings closer to our line-of-sight to the Sun. Closest to the Earth-Sun line but passing about 8 degrees north of the Sun on March 25, Venus will reach a (non-judgmental) inferior conjunction. Soon after, Venus will shine clearly above the eastern horizon in predawn skies as planet Earth's morning star.
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