Messier 100 — Galaxy in Coma Berenices

M100 is a grand-design spiral galaxy in the constellation Coma Berenices, located approximately 55 million light-years from Earth. It is one of the brightest and largest members of the Virgo Cluster. Classified as type SAB(s)bc, it displays two prominent, well-defined spiral arms that are beautifully symmetric and studded with young blue star clusters and pinkish HII regions. The galaxy is seen nearly face-on, providing a textbook view of spiral structure. M100 spans about 107,000 light-years in diameter, comparable to the Milky Way. Its central region contains a smaller, secondary bar and a mini-spiral structure visible in high-resolution images.

Located in Coma Berenices, about 7 degrees north of the center of the Virgo Cluster. At magnitude 9.3, M100 is one of the brighter Virgo Cluster galaxies and can be detected in large binoculars as a faint fuzzy spot. A 4-inch telescope shows a round, diffuse glow with a brighter center. An 8-inch telescope under dark skies begins to show the extent of the disk. A 12-inch or larger telescope may reveal hints of the two main spiral arms with averted vision. M100 rewards patience and dark adaptation. Best observed from March through June when Coma Berenices is high overhead.

Discovered by Pierre Mechain on March 15, 1781, and cataloged by Messier on April 13, 1781. In 1994, M100 became one of the first galaxies observed by the repaired Hubble Space Telescope, which identified Cepheid variable stars within it. These Cepheids provided a crucial calibration point for the cosmic distance ladder and helped determine the Hubble constant. Five supernovae have been observed in M100, including SN 1979C and SN 2006X.