101 Must-See Cosmic Objects: M109

The third-largest constellation in the sky, Ursa Major, contains seven Messier objects. Five are galaxies. The least observed of these — based on the number of books and articles featuring it — is M109, also known as NGC 3992. Messier’s original catalog topped out at 103, but today, astronomers recognize 109 objects.

Discovered in 1781 by Pierre Méchain, M109 is the most distant Messier object, located a whopping 83.5 million light-years away. (The closest is M45, the