Have you ever seen a fireball? In astronomy, a fireball is a very bright meteor -- one at least as bright as Venus and possibly brighter than even a full Moon. Fireballs are rare -- if you see one you are likely to remember it for your whole life. Physically, a fireball is a small rock that originated from an asteroid or comet that typically leaves a fading smoke trail of gas and dust as it shoots through the Earth's atmosphere. It is unlikely that any single large ground strike occurred -- much of the rock likely vaporized as it broke up into many small pieces. The featured picture was captured last week from a deadwood beach in Cape San Blas, Florida, USA. Piece it Back Together: Astronomy Puzzle 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.
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
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.
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.
This month, bright planet Saturn rises in evening skies, its rings oriented nearly edge-on when viewed from planet Earth. And in the early morning hours on July 6, it posed very briefly with the International Space Station when viewed from a location in Federal Way, Washington, USA. This well-planned image, a stack of video frames, captures their momentary conjunction in the same telescopic field of view. With the ISS in low Earth orbit, space station and gas giant planet were separated by almost 1.4 billion kilometers. Their apparent sizes are comparable but the ISS was much brighter than Saturn and the ringed planet's brightness has been increased for visibility in the stacked image. Precise timing and an exact location were needed to capture the ISS/Saturn conjunction.
