The APODs (Featured Link on the right) continue to be spectacular. Here are my favs from the past few weeks. Descriptions below the jump.
Ghostly Zodiacal light, featured near the center of this remarkable panorama, is produced as sunlight is scattered by dust in the Solar System’s ecliptic plane. In the weeks surrounding the March equinox (today at 1732 UT) Zodiacal light is more prominent after sunset in the northern hemisphere, and before sunrise in the south, when the ecliptic makes a steep angle with the horizon. In the picture, the narrow triangle of Zodiacal light extends above the western horizon and seems to end at the lovely Pleiades star cluster. Arcing above the Pleiades are stars and nebulae along the plane of our Milky Way Galaxy. Recorded on March 10 from Teide National Park on the island of Tenerife, the vista is composed of 4 separate pictures spanning over 180 degrees.
What’s happening in the middle of this massive galaxy? There, two bright sources at the center of this composite x-ray (blue)/radio (pink) image are thought to be co-orbiting supermassive black holes powering the giant radio source 3C 75. Surrounded by multimillion degree x-ray emitting gas, and blasting out jets of relativistic particles the supermassive black holes are separated by 25,000 light-years. At the cores of two merging galaxies in the Abell 400 galaxy cluster they are some 300 million light-years away. Astronomers conclude that these two supermassive black holes are bound together by gravity in a binary system in part because the jets’ consistent swept back appearance is most likely due to their common motion as they speed through the hot cluster gas at 1200 kilometers per second. Such spectacular cosmic mergers are thought to be common in crowded galaxy cluster environments in the distant universe. In their final stages the mergers are expected to be intense sources of gravitational waves.
What creates these picturesque dark streaks on Mars? No one knows for sure. A leading hypothesis is that streaks like these are caused by fine grained sand sliding down the banks of troughs and craters. Pictured above, dark sand appears to have flowed hundreds of meters down the slopes of Acheron Fossae. The sand appears to flow like a liquid around boulders, and, for some reason, lightens significantly over time. This sand flow process is one of several which can rapidly change the surface of Mars, with other processes including dust devils, dust storms, and the freezing and melting of areas of ice. The above image was taken by the HiRise camera on board the Mars Reconnaissance Orbiter which has been orbiting Mars since 2006. Acheron Fossae is a 700 kilometer long trough in the Diacria quadrangle of Mars.
International Space Station seen from above.