Astronomy Picture Of the Day (APOD)Deep Field: Nebulae of Sagittarius
These three bright nebulae are often featured on telescopic tours of the constellation Sagittarius and the crowded starfields of the central Milky Way. In fact, 18th century cosmic tourist Charles Messier cataloged two of them; M8, the large nebula just left of center, and colorful M20 on the top left.
Planets of the Solar System: Tilts and Spins
How does your favorite planet spin? Does it spin rapidly around a nearly vertical axis, or horizontally, or backwards? The featured video animates NASA images of all eight planets in our Solar System to show them spinning side-by-side for an easy comparison.
A Circumhorizontal Arc Over Ohio
Why would clouds appear to be different colors? The reason here is that ice crystals in distant cirrus clouds are acting like little floating prisms. Sometimes known as a fire rainbow for its flame-like appearance, a circumhorizon arc lies parallel to the horizon.
Atlas, Daphnis, and Pan
Atlas, Daphnis, and Pan are small, inner, ring moons of Saturn. They are shown at the same scale in this montage of images by the Cassini spacecraft that made its grand final orbit of the ringed planet in September 2017. In fact, Daphnis was discovered in Cassini images from 2005.
Pulsating RS Puppis, the brightest star in the image center, is some ten times more massive than our Sun and on average 15,000 times more luminous. In fact, RS Pup is a Cepheid...
Dark Skies: Turn on the Night
Have you ever experienced a really dark night sky? One common and amazing feature is the glowing band of our Milky Way galaxy stretching from horizon to horizon. If you live in or near...
Anemic Spiral NGC 4921 from Hubble
How far away is spiral galaxy NGC 4921? It's surpringly important to know. Although presently estimated to be about 300 million light years distant, a more precise determination could be coupled with its known recession speed to help humanity better calibrate the expansion rate of the entire visible universe.
Young Star Cluster Trumpler 14 from Hubble
Why does star cluster Trumpler 14 have so many bright stars? Because it is so young. Many cluster stars have formed only in the past 5 million years and are so hot they emit detectable X-rays.
Rho Ophiuchi Wide Field
The colorful clouds surrounding the star system Rho Ophiuchi compose one of the closest star forming regions. Rho Ophiuchi itself is a binary star system visible in the blue reflection nebula just to the left of the image center.
Ash and Lightning above an Icelandic Volcano
Why did a picturesque volcanic eruption in Iceland create so much ash? Although the large ash plume was not unparalleled in its abundance, its location was particularly noticeable because it drifted across such well-populated areas.