M33 was cataloged by Charles Messier on August 25, 1764. Nicknamed the Triangulum Galaxy, M33 is a spiral galaxy that contains between 10 and 40 billion stars. It is about 3 million light years away when observed from earth, or just past the Andromeda Galaxy. A spiral galaxy is a spiral-shaped system of stars, dust, and gas clouds.1 M33 contains one of the largest known HII regions, a "diffuse emission nebula containing ionized hydrogen," measuring 1500 light years across.2 It is the small red area just above and to the right of the yellow center of the galaxy. M33 is found in the Triangulum constellation, and under excellent conditions, can be seen from earth with the naked eye. The field of view of this photograph displays 956.3 arc seconds top to bottom. If the galaxy is 3 million light years away, therefore, this photograph has a linear scale of 13,909 light years.
The Triangulum Galaxy contains interstellar clouds of stars, gas, and dust set into an overall glow of starlight.3 The blue-tinted areas in M33 are where stars are currently forming. New stars burn hotter, and therefore more blue in color, than their older counterparts. We can only see the most massive and hot clusters of the new stars. The red-tinted areas in the photograph are HII regions made up of hydrogen gas. The dark regions contrasted against the yellow glow are clouds of dust that block light and obscure the objects behind them. At the very center of M33, there is a clearly defined nuclear bulge characterized by a pale but bright yellow tint.
1 "Glossary." Hubble Site. <http://hubblesite.org/reference_desk/glossary/index.php?topic=topic_galaxies>.
2 Frommert, Hartmut and Kronberg, Christine. "Messier 33." Students for the Exploration and Development of Space. <http://messier.seds.org/m/m033.html>
3 Comins, Neil F. and Kaufmann, William J. III. (1999). Discovering the Universe. New York: W.H. Freeman and Company.
|Right Ascension (J2000)||01:33:51|
|Filters used||B (Blue), C (Clear), R (Red), V (Green)|
|Exposure time per filter||B, V, R, and C (60s x 5)|
|Date observed||October 18, 2011|