In the vast Orion Molecular Cloud complex, several bright blue nebulas are particularly apparent. Pictured here are two of the most prominent reflection nebulas – dust clouds lit by the reflecting light of bright embedded stars. The more famous nebula is M78, in the image center, cataloged over 200 years ago. To its left is the lesser known NGC 2071. Astronomers continue to study these reflection nebulas to better understand how interior stars form. The Orion complex lies about 1500 light-years distant, contains the Orion and Horsehead nebulas, and covers much of the constellation of Orion.
If you could circle the Earth aboard the International Space Station, what might you see? Some amazing vistas, one of which was captured in this breathtaking picture in mid-2015. First, visible at the top, are parts of the space station itself including solar panels. Just below the station is the band of our Milky Way Galaxy, glowing with the combined light of billions of stars, but dimmed in patches by filaments of dark dust. The band of red light just below the Milky Way is airglow — Earth’s atmosphere excited by the Sun and glowing in specific colors of light. Green airglow is visible below the red. Of course that’s our Earth below its air, with the terminator between day and night visible near the horizon. As clouds speckle the planet, illumination from a bright lightning bolt is seen toward the lower right. Between work assignments, astronauts from all over the Earth have been enjoying vistas like this from the space station since the year 2000.
Large spiral galaxy NGC 891 spans about 100 thousand light-years and is seen almost exactly edge-on from our perspective. In fact, about 30 million light-years distant in the constellation Andromeda, NGC 891 looks a lot like our Milky Way. At first glance, it has a flat, thin, galactic disk of stars and a central bulge cut along the middle by regions of dark obscuring dust. But remarkably apparent in NGC 891’s edge-on presentation are filaments of dust that extend hundreds of light-years above and below the center line. The dust has likely been blown out of the disk by supernova explosions or intense star formation activity. Fainter galaxies can also be seen near the edge-on disk in this deep portrait of NGC 891. (Editor’s Note: The NGC 891 image used in today’s APOD posting has been replaced and the credit corrected to indicate the author of the original work.)
Mimas is an icy, crater-pocked moon of Saturn a mere 400 kilometers (250 miles) in diameter. Its largest crater Herschel is nearly 140 kilometers wide. About a third the diameter of Mimas itself, Herschel crater gives the small moon an ominous appearance, especially for scifi fans of the Death Star battlestation of Star Wars fame. In fact, only a slightly bigger impact than the one that created such a large crater on a small moon could have destroyed Mimas entirely. In this Cassini image from October 2016, the anti-Saturn hemisphere of the synchronously rotating moon is bathed in sunlight, its large crater near the right limb. Casting a long shadow across the crater floor, Herschel’s central mountain peak is nearly as tall as Mount Everest on planet Earth.
What’s happening in the center of spiral NGC 5033? Many things — some circular, some energetic, and some not well understood. NGC 5033 is known as a Seyfert galaxy because of the great activity seen in its nucleus. Bright stars, dark dust, and interstellar gas all swirl quickly around a galactic center that appears slightly offset from a supermassive black hole. This offset is thought to be the result of NGC 5033 merging with another galaxy sometime in the past billion years. The featured image was taken by the Hubble Space Telescope in 2005. NGC 5033 spans about 100,000 light years and is so far away that we see it only as it existed about 40 million years ago.
Moonset on January 1 is captured in this sea and night sky snapshot from the port city of New York. Its warm moonlight shining through haze and thin clouds, this New Year’s Moon was about 3 days old, in a waxing crescent phase. The visible lunar disk is about 10 percent illuminated. Also easy to spot in hazy urban skies, Venus blazes forth over the western horizon, begining the year as Earth’s evening star. Like the Moon, Venus goes through a range of phases as seen from planet Earth. As the year began, telescopic views of the brilliant inner planet’s disk would show it about 50 percent illuminated, growing into a larger but thinner crescent by early March. New York Harbor’s welcoming beacon, the Statue of Liberty, anchors a terrestrial corner of the night’s triangle at the far left.
An old comet has returned to the inner Solar System. Not only is Comet 45P/Honda–Mrkos–Pajdušáková physically ancient, it was first discovered 13 orbits ago in 1948. Comet 45P spends most of its time out near the orbit of Jupiter and last neared the Sun in 2011. Over the past few months, however, Comet 45P‘s new sunward plummet has brightened it considerably. Two days ago, the comet passed the closest part of its orbit to the Sun. The comet is currently visible with binoculars over the western horizon just after sunset, not far from the much brighter planet Venus. Pictured, Comet 45P was captured last week sporting a long ion tail with impressive structure. Comet 45P will pass relatively close to the Earth early next month.
Higher than the highest building, higher than the highest mountain, higher than the highest airplane, lies the realm of the aurora. Auroras rarely reach below 60 kilometers, and can range up to 1000 kilometers. Aurora light results from energetic electrons and protons striking molecules in the Earth’s atmosphere. Frequently, when viewed from space, a complete aurora will appear as a circle around one of the Earth’s magnetic poles. The featured wide-angle image, horizontally compressed, captured an unexpected auroral display that stretched across the sky five years ago over eastern Norway.