The spiral galaxy M91 was discovered by Charles Messier in 1781. It was the last of the nine objects (M84 - M92) that Messier added to his catalog on a single night in March.
Located 60 million light-years from Earth with an apparent magnitude of only 11, M91 is one of the faintest objects in Messier’s catalog.
M91 is one of over a thousand galaxies that make up the Virgo cluster — a group of galaxies that are gravitationally bound to one another. It is an anemic galaxy, meaning that it has a lower rate of star formation compared to other spiral galaxies.
Messier 91 (also known as NGC 4548 or M91) is a barred spiral galaxy located in the Coma Berenices constellation and is part of the Virgo Cluster of galaxies. M91 is about 63 million light-years away from the earth. It was the last of a group of eight nebulae discovered by Charles Messier in 1781. Originally M91 was a missing Messier object in the catalogue as the result of a bookkeeping mistake by Messier.
Facts about M91 by Keith Turnecliff
It can be spotted with medium-sized telescopes in the constellation Coma Berenices most easily during May.