M33, the Triangulum Galaxy, is a perennial favorite of amateur and
professional astronomers alike, due to its orientation and relative
proximity to us. It is the second nearest spiral galaxy to our Milky Way
(after M31, the Andromeda Galaxy) and a prominent member of the "local
group" of galaxies. From our Milky Way perspective, M33's stellar disk
appears at moderate inclination, allowing us to see its internal structure
clearly, whereas M31 is oriented nearly edge-on.
The Galaxy Evolution Explorer imaged M33 as it appears in ultraviolet
wavelengths. Ultraviolet imaging primarily traces emission from the
atmospheres of hot stars, most of which formed in the past few hundred
million years. These data provide a reference point as to the internal
composition of a typical star-forming galaxy and will help scientists
understand the origin of ultraviolet emission in more distant galaxies.
These observations of M33 allow astronomers to compare the population of
young, massive stars with other components of the galaxy, such as
interstellar dust and gas, on the scale of individual giant molecular
clouds. The clouds contain the raw material from which stars form. This
presents direct insight into the star formation process as it occurs
throughout an entire spiral galaxy and constitutes a unique resource for
broader studies of galaxy evolution.