NGC 891 (also known as Caldwell 23, the Silver Sliver Galaxy, and the Outer Limits Galaxy) is an edge-on unbarred spiral galaxy about 30 millionlight-years away in the constellationAndromeda. It was discovered by William Herschel on October 6, 1784. The galaxy is a member of the NGC 1023 group of galaxies in the Local Supercluster. It has an H II nucleus.The object is visible in small to moderate size telescopes as a faint elongated smear of light with a dust lane visible in larger apertures.In 1999, the Hubble Space Telescope imaged NGC 891 in infrared.In 2005, due to its attractiveness and scientific interest, NGC 891 was selected to be the first light image of the Large Binocular Telescope.In 2012, it was again used as a first light image of the Lowell Discovery Telescope with the Large Monolithic Imager.Supernova SN 1986J was discovered on August 21, 1986 at apparent magnitude 14.
The galaxy is a member of a small group of galaxies, sometimes called the NGC 1023 Group. Other galaxies in this group are the NGCs 925, 949, 959, 1003, 1023, and 1058, and the UGCs 1807, 1865 (DDO 19), 2014 (DDO 22), 2023 (DDO 25), 2034 (DDO 24), and 2259. Its outskirts are populated by multiple low-surface brightness, coherent, and vast substructures, like giant streams that loop around the parent galaxy up to distances of approximately 50 kpc. The bulge and the disk are surrounded by a flat and thick cocoon-like stellar structure. These have vertical and radial distances of up to 15 kpc and 40 kpc, respectively,[15] and are interpreted as the remnant of a satellite galaxy disrupted and in the process of being absorbed by NGC 891.
 Visible in the constellation of Andromeda, NGC 891 is located approximately 30 million light-years away from Earth. The galaxy, spanning some 100,000 light-years, is seen exactly edge-on, and reveals its thick plane of dust and interstellar gas. While initially thought to look like our own Milky Way if seen from the side, more detailed surveys revealed the existence of filaments of dust and gas escaping the plane of the galaxy into the halo over hundreds of light-years. They can be clearly seen here against the bright background of the galaxy halo, expanding into space from the disk of the galaxy.Astronomers believe these filaments to be the result of the ejection of material due to supernovae or intense stellar formation activity. By lighting up when they are born, or exploding when they die, stars cause powerful winds that can blow dust and gas over hundreds of light-years in space.A few foreground stars from the Milky Way shine brightly in the image, while distant elliptical galaxies can be seen in the lower right of the image.NGC 891 is part of a small group of galaxies bound together by gravity.

Other tidbits of trivia: Hollywood found the galaxy’s image so compelling that it appears in the credits sequence of The Outer Limits — among other objects described in Astronomy’s June 2019 story “The Outer Limits universe.” The soundtrack for John Carpenter’s 1974 film Dark Star included a track called “When Twilight Falls on NGC 891.” That same year, Edgar Froese released an album that included the song “NGC 891.”