The spiral galaxy M33 also is called the Triangulum Galaxy for the constellation in which it resides. About four times smaller (in radius) than our Milky Way Galaxy and the Andromeda Galaxy (M31), it is much larger than the many of the local dwarf spheroidal galaxies. The galaxy's proximity to M31 causes it to be thought by some to be a satellite galaxy of this more massive galaxy.
In the above picture, visible light is shown in red and ultraviolet light superposed in blue. Stars in M33 are the most distant ever to be studied spectroscopically.
Image credit: NASA, UIT