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NASA Astronomy Picture of the Day:

Can some supernovas explode twice? Yes, when the first explosion acts like a detonator for the second. This is a leading hypothesis for the cause of supernova remnant (SNR) 0509-67.5. In this two-star system, gravity causes the larger and fluffier star to give up mass to a smaller and denser white dwarf companion. Eventually the white dwarf's near-surface temperature goes so high that it explodes, creating a shock wave that goes both out and in -- and so triggers a full Type Ia supernova near the center. Recent images of the SNR 0509-67.5 system, like the featured image from the Very Large Telescope in Chile, show two shells with radii and compositions consistent with the double detonation hypothesis. This system, SNR 0509-67.5 is also famous for two standing mysteries: why its bright supernova wasn't noted 400 years ago, and why no visible companion star remains.

An Airstream Safari trailer in Joshua Tree National Park at dusk. Airstream founder Wally Byam died on this day in 1962.

Dllu, CC BY-SA 4.0, via Wikimedia Commons. View source.

Mary Ann Evans (1819 - 1880) Also known by her pen name George Eliot, was one of the leading English writers of the Victorian era .

NASA Astronomy Picture of the Day:

Nebulas are perhaps as famous for being identified with familiar shapes as perhaps cats are for getting into trouble. Still, no known cat could have created the vast Cat's Paw Nebula visible toward the constellation of the Scorpion (Scorpius). At 5,700 light years distant, Cat's Paw is an emission nebula within a larger molecular cloud. Alternatively known as the Bear Claw Nebula and cataloged as NGC 6334, stars nearly ten times the mass of our Sun have been born there in only the past few million years. Pictured here is a recently released image of the Cat's Paw taken in infrared light by the James Webb Space Telescope. This newly detailed view into the nebula helps provide insight for how turbulent molecular clouds turn gas into stars. Explore Your Universe: Random APOD Generator

SQM "Boxcabs" 603 and 607 hauling empty nitrate hoppers from Tocopilla to Barriles, Chile.

Kabelleger / David Gubler (http://www.bahnbilder.ch), CC BY-SA 3.0, via Wikimedia Commons. View source.

NASA Astronomy Picture of the Day:

About 1,300 images from the Lunar Reconnaissance Orbiter spacecraft's wide angle camera were used to compose this spectacular view of a familiar face - the lunar nearside. But why is there a lunar nearside? The Moon rotates on its axis and orbits the Earth at the same rate, about once every 28 days. Tidally locked in this configuration, the synchronous rotation always keeps one side, the nearside, facing Earth. As a result, featured in remarkable detail in the full resolution mosaic, the smooth, dark, lunar maria (actually lava-flooded impact basins), and rugged highlands, are well-known to earthbound skygazers. To find your favorite mare or large crater, just follow this link or slide your cursor over the picture. The LRO images used to construct the mosaic were recorded over a two week period in December 2010.

Goëngarijpsterpoelen (Frysk), or Goaiïngarypster Puollen. View of the lake from Heerenzijl. The first rays of sunshine in the morning dispel the mist, and shine on the trees and the reeds.

Dominicus Johannes Bergsma, CC BY-SA 4.0, via Wikimedia Commons. View source.

NASA Astronomy Picture of the Day:

The sixth object in Charles Messier's famous catalog of things which are not comets, Messier 6 is a galactic or open star cluster. A gathering of 100 stars or so, all around 100 million years young, M6 lies some 1,600 light-years away toward the central Milky Way in the constellation Scorpius. Also cataloged as NGC 6405, the pretty star cluster's outline suggests its popular moniker, the Butterfly Cluster. Surrounded by diffuse reddish emission from the region's hydrogen gas the cluster's mostly hot and therefore blue stars are near the center of this colorful cosmic snapshot. But the brightest cluster member is a cool K-type giant star. Designated BM Scorpii it shines with a yellow-orange hue, seen near the end of one of the butterfly's antennae. This telescopic field of view spans nearly 2 Full Moons on the sky. That's 25 light-years at the estimated distance of Messier 6.

Photo by Xinran Li

STS-135 final flyaround of ISSThis picture of the International Space Station was photographed from the space shuttle Atlantis as the orbiting complex and the shuttle performed their relative separation in the early hours of July 19, 2011. Onboard the station were Russian cosmonauts Andrey Borisenko, Expedition 28 commander; Sergei Volkov and Alexander Samokutyaev, both flight engineers; Japan Aerospace Exploration astronaut Satoshi Furukawa, and NASA astronauts Mike Fossum and Ron Garan, all flight engineers. Onboard the shuttle were NASA astronauts Chris Ferguson, STS-135 commander; Doug Hurley, pilot; and Sandy Magnus and Rex Walheim, both mission specialists.

NASA, Public domain, via Wikimedia Commons. View source.