The lovely pinwheel spiral galaxy M33 in the constellation Triangulum is likely the most distant object you can see with your unaided eye. Sometimes called the Triangulum galaxy, M33 is one of three spirals in our Local Group along with the Andromeda Galaxy and our own Milky Way. It displays lovely associations of blue-white stars along its loose spiral arms, along with many rose-pink star forming regions. The emission nebula NGC 604 is especially striking. This star factory in M33 is nearly 3 million light years away but still lies within reach of a backyard telescope.
How is it possible to see this nebula from such a great distance? NGC 604 lies within reach of a small telescope because of its enormous size and brightness. It’s about 1,500 light years across, forty times larger than the Orion Nebula (M42) and about as large as the Orion Nebula is distant from us. It shines some 6,000 times brighter that M42. If NGC 604 replaced the Orion Nebula, it would shine as bright as the planet Venus, although the light would spread across a patch of sky as large as your outstretched hand.
First seen by William Herschel in 1784, NGC 604 is the second-largest emission nebula in the Local Group of galaxies. Only the Tarantula Nebula in the Large Magellanic is larger.
If you have a small telescope and dark, clear sky, look for NGC 604 about 12′ northeast of the nucleus of the Triangulum. The nebula is sometimes mistaken for the 10th magnitude star about 1′ to the southeast. A UHC or OIII light pollution filter will help, as will a moderately high magnification of 100-150x.
NGC 604 is set aglow by a cluster of blazing-hot O-type stars near its middle. The light and radiation from these stars blows a hole in the middle of the nebula and gives us a clearer view of the innards of the star forming region.
Many more regions of glowing ionized hydrogen in M33 lie within the reach of imagers with small telescopes. The image above, courtesy of astrophotographer Jeff Johnson of New Mexico, shows many such reddish-pink regions in M33. NGC 604 is located at the upper right edge of the galaxy in this image. See more of Jeff’s work at jeffjastro.com.
Publisher’s Note: M33 and NGC 604 in Triangulum are two of nearly 100 objects features in the guide “What to See in a Small Telescope: October – December”. Click here to learn more about this guide…