Astr111 Photography Projects, Fall 2005

M33 Triangulum Galaxy, Laura Hollingsworth

The Triangulum galaxy M33 is a member of the "Local Group" of galaxies which include the Andromeda galaxy M31, and our own Milky Way galaxy. This galaxy is smaller then both of these galaxies, but would be considered an average size for spiral galaxies in the universe. Its popular names include the Pinwheel Galaxy or just the Triangulum galaxy. M33 was probably first found by Hodierna before 1654. It was independently rediscovered by Charles Messier, and cataloged by him on August 25, 1764. William Herschel gave it the number "H V.17", based on an observation dated September 11, 1784. Also, the brightest and largest HII region (a diffuse emission nebula containing ionized hydrogen) has been given a NGC number of its own (NGC 604) because of the cataloging of Herschel (It is situated in the northeastern part of the galaxy).

This galaxy was nick-named the "pinwheel galaxy" because of the spiral arms that extend from the bright center. William Herschel described it as a "a faint, extended milky Ray of about 17' in length and 12' in breadth". It is brightest and broadest in the middle, while the the spirals are fainter and less defined than those of other spiral galaxies. Newly formed stars are brightest in the outer bands. There is a small, round, very faint nebula just north of it which is also characterized by a brighter spot. It is almost far enough away to form a seperate nebula. The linear size of this galaxy is 17,453.2 lightyears.

References:
The Messier Catalog

Astronomy Picture of the Day

DeepSky Observer's Companion