The Triangulum Galaxy gets its name from being the largest-appearing galaxy in the constellation Triangulum. It is approximately 2.5 million light-years from Earth and may be gravitationally bound to the Great Andromeda Galaxy, M31, which is about three times larger. The Triangulum Galaxy is cataloged as M33 and NGC 598.

The Triangulum Galaxy is home to one of the largest known emission nebulae, seen at the 1 o’clock position glowing in the red light emitted by ionized hydrogen gas. The nebula is so large that it was given its own catalog entry when it was discovered by William Herschel in 1784 and is now known as NGC 604. It is over 40 times the size of the Orion Nebula and contains a cluster of relatively newly formed, massive stars at its center.

128 minutes L and 144 minutes RGB (binned 2x2) on 2013-01-07 and 176 minutes H-a on 2013-01-26 using a QSI 583 from northern New Jersey through an Astro-Physics 155mm refractor at f5.4. North is to the right. ©2013

M33, detail from the above image.