NGC 891 is a tenth magnitude unbarred spiral galaxy located in Andromeda. Also known as the Silver Sliver, it's one of the best examples of an edge-on galaxy in the sky, although a challenging object for small scopes. Due to its attractiveness and scientific appeal, NGC 891 was selected on October 12, 2005 to be the first light image of the Large Binocular Telescope at Mount Graham International Observatory in Arizona. In 2012, it was again selected as first light image, this time for the Discovery Channel Telescope (DCT) Large Monolithic Imager at the Lowell Observatory in Happy Jack, Arizona.
The Silver Sliver was discovered by William Herschel on October 6, 1784 and is best seen from the Northern Hemisphere during October, November and December. Astronomers think that our Milky Way galaxy would look remarkably similar if viewed edge-on.
The Silver Sliver is located in eastern Andromeda close to the Perseus border. It's positioned 3.5 degrees east of beautiful double star Almach (γ And - mag. +2.1) with naked-eye open cluster M34 (mag. +5.5) a further 3.5 degrees eastwards, in Perseus.
At mag. +10.0, NGC 891 is a difficult small telescope object. From a dark site it's possible to spot it with a small 80mm (3.1 inch) scope but only as a faint thin slither of light. However, for most observers a larger scope is required. A 200mm (8-inch) instrument shows a thin needle of nebulosity with a bright central core. On nights of good seeing a narrow dust lane bisecting the galaxy's long axis can be seen. Large amateur scopes show variations in the dust band with many foreground stars populating the view. Whatever type of instrument you're using, the best views of this object require dark skies with magnifications greater than 100x recommended. In total, NGC 891 covers 13.5 x 2.5 arc minutes of apparent sky.
The Silver Sliver is number 23 in the Caldwell catalogue. It's about 30 million light-years distant and has an actual diameter of 120,000 light-years. The galaxy is estimated to contain about 500 billion stars and is the dominant member of the NGC 1023 group of galaxies, which also includes NGC 1023, NGC 925, NGC 1058, NGC 1239 and many other smaller dwarf galaxies.
On August 21, 1986, a supernova (SN 1986J) that peaked at mag. +14 was discovered in NGC 891.
NGC 891 Data Table
|Object Type||Unbarred Spiral Galaxy|
|Distance (ly)||30 Million|
|RA (J2000)||02h 22m 33s|
|DEC (J2000)||42d 21m 03s|
|Apparent Size (arc mins)||13.5 x 2.5|
|Number of Stars||500 Billion|
|Notable Feature||Member of the NGC 1023 group of galaxies|