The distribution of galaxies in the night sky is not random. They tend to congregate in groups or clusters, and our own Local Group, which includes the Milky Way, is very far from being exceptional. For instance, the Virgo Cluster, at a distance of around 60 million light-years, contains approximately 1500 members and some (such as M100, a grand design spiral galaxy) are much more massive than our galaxy.

Galaxy M100
M100 is a grand design spiral galaxy that presents an intricate structure, with a bright core and two prominent arms. ESO/IDA/Danish 1.5 m/R. Gendler, J.-E. Ovaldsen, C. C. Thone and C. Feron

M100 can be spotted with large binoculars and backyard telescopes in Coma Berenices, a faint constellation representing the locks of the Egyptian Queen Berenice, which she offered to the gods for the return of her husband from battle. M100 is the brightest and largest spiral galaxy in the Virgo Cluster and has a “grand design”, meaning that it has two symmetrically placed spiral arms that extend over most of its visible disk in professional telescopic images.

The galaxy is located 8° east of second-magnitude Denebola (Beta Leonis), and 2° northeast of the fifth-magnitude star 6 Comae Berenices. Through an 8-inch scope at low to medium power, look for a soft, round glow about 6′ across. You will not see M100’s spiral arms until you crank the magnification past 200X, and then only on the best nights.

The arms appear as brighter regions just to the east and west of the nucleus. Through a 12-inch telescope, the spiral structure can be traced twice as far from the core. Two faint dwarf galaxies lie to the north and east. Magnitude +13.9 NGC 4322, to the north, appears to be M100’s true companion, while magnitude +13.3 NGC 4328 lies in the foreground to the east.

Long-exposure photography has shown M100 to be far larger than previously believed, with a substantial portion of its mass contained in faint outer regions. The Hubble Space Telescope discovered over twenty Cepheid variables and one nova in M100 and was able to accurately determine its distance as 55 million light-years. Five supernova events have been observed in this galaxy – one as recently as February 2006!

Finder map – field width 15°, stars to magnitude +8.5.