Star Trails of the North and South Image Credit & Copyright: Saeid Parchini
Explanation: What divides the north from the south? It all has to do with the spin of the Earth. On Earth’s surface, the equator is the dividing line, but on Earth’s sky, the dividing line is the Celestial Equator — the equator’s projection onto the sky. You likely can’t see the Earth’s equator around you, but anyone with a clear night sky can find the Celestial Equator by watching stars move. Just locate the dividing line between stars that arc north and stars that arc south. Were you on Earth’s equator, the Celestial Equator would go straight up and down. In general, the angle between the Celestial Equator and the vertical is your latitude. The featured image combines 325 photos taken every 30 seconds over 162 minutes. Taken soon after sunset earlier this month, moonlight illuminates a snowy and desolate scene in northwest Iran. The bright streak behind the lone tree is the planet Venus setting.
Explanation: Interstellar clouds of hydrogen gas and dust abound in this gorgeous skyscape. The 3 degree wide field of view stretches through the faint but fanciful constellation Monoceros, the Unicorn. A star forming region cataloged as NGC 2264 is centered, a complex jumble of cosmic gas, dust and stars about 2,700 light-years distant. It mixes reddish emission nebulae excited by energetic light from newborn stars with dark dust clouds. Where the otherwise obscuring dust clouds lie close to hot, young stars they also reflect starlight, forming blue reflection nebulae. A few light-years across, a simple sculpted shape known as the Cone Nebula is near center. Outlined by the red glow of hydrogen gas, the cone points toward the left and bright, blue-white S Monocerotis. Itself a multiple system of massive, hot stars S Mon is adjacent to bluish reflection nebulae and the convoluted Fox Fur nebula. Expansive dark markings on the sky are silhouetted by a larger region of fainter emission with yellowish open star cluster Trumpler 5 near the top of the frame. The curious compact cometary shape right of center is known as Hubble’s Variable Nebula.
NGC 7331 Close Up Image Credit & License: ESA/Hubble & NASA/D. Milisavljevic (Purdue University)
Explanation: Big, beautiful spiral galaxy NGC 7331 is often touted as an analog to our own Milky Way. About 50 million light-years distant in the northern constellation Pegasus, NGC 7331 was recognized early on as a spiral nebula and is actually one of the brighter galaxies not included in Charles Messier’s famous 18th century catalog. Since the galaxy’s disk is inclined to our line-of-sight, long telescopic exposures often result in an image that evokes a strong sense of depth. In this Hubble Space Telescope close-up, the galaxy’s magnificent spiral arms feature dark obscuring dust lanes, bright bluish clusters of massive young stars, and the telltale reddish glow of active star forming regions. The bright yellowish central regions harbor populations of older, cooler stars. Like the Milky Way, a supermassive black hole lies at the core of spiral galaxy NGC 7331.
Explanation: The Moon’s south pole is near the top of this detailed telescopic view. Looking across the rugged southern lunar highlands it was captured from southern California, planet Earth. At the Moon’s third quarter phase the lunar terminator, the sunset shadow line, is approaching from the left. The scene’s foreshortened perspective heightens the impression of a dense field of craters and makes the craters themselves appear more oval shaped close to the lunar limb. Below and left of center is sharp-walled crater Tycho, 85 kilometers in diameter. Young Tycho’s central peak is still in sunlight, but casts a long shadow across the crater floor. The large prominent crater to the south (above) Tycho is Clavius. Nearly 231 kilometers in diameter its walls and floor are pocked with smaller, more recent, overlaying impact craters. Mountains visible along the lunar limb at the top can rise about 6 kilometers or so above the surrounding terrain.