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The Triangulum Galaxy Messier 33 (M33, NGC 598) is another prominent member of the Local Group of galaxies. This galaxy is small compared to its big apparent neighbor, the Andromeda galaxy M31, and to our Milky Way galaxy, but more of an average size for spiral galaxies in the universe. M33 may be a remote but gravitationally bound companion of the Andromeda galaxy M31.

Several knots in the spiral arms of M33 have been assigned their own NGC catalog numbers - the largest of which in this image is in the lower mid-left and is NGC 604. This is one of the largest H II regions known at all: it has a diameter of nearly 1500 light-years, and a spectrum similar to the Orion nebula M42. Over 200 young hot massive stars (of 15 to 60 solar masses) have recently formed here.

Some other catalogued objects are identified in this map.

December 11, 2009