Object Type: Galaxy + Galaxy Cluster
Scope: AP 5" Refractor
Exposure 140 minutes
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 million light-years away in the constellation Andromeda. 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.
NGC 891 looks as the Milky Way would look like when viewed edge-on (some astronomers have even noted how similar to NGC 891 our galaxy looks as seen from the Southern Hemisphere) and, in fact, both galaxies are considered very similar in terms of luminosity and size; studies of the dynamics of its molecular hydrogen have also proven the likely presence of a central bar. Despite this, recent high-resolution images of its dusty disk show unusual filamentary patterns. These patterns are extending into the halo of the galaxy, away from its galactic disk. Scientists presume that supernova explosions caused this interstellar dust to be thrown out of the galactic disk toward the halo.
Less than 1 degree from NGC 891 is Abell 347 galaxy cluster. This image shows many of the most prominent members of the galaxy group, including 7 galaxies listed in the New General Catalog about 20 galaxies listed in the Principal Galaxy Catalog.
The distance to this cluster is about 240 million light years. The galaxies are moving away from us at about 1.9% of the speed of light.