M100
Mirror Galaxy
Spiral
Properties
Position & Identifiers
Visibility
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About M100
Description
M100 (also called the Mirror Galaxy) is a grand-design spiral galaxy in Coma Berenices, about 55 million light-years from Earth. It is one of the brightest and largest spirals in the Virgo Cluster, spanning about 107,000 light-years. Its two prominent, symmetric spiral arms are studded with blue star-forming regions and are among the best-defined of any Virgo galaxy.
Observing Tips
Located about 2 degrees north of M98, in the northern part of the Virgo Cluster. In a telescope it appears as a large, round, bright glow with a strong central concentration. The spiral arms require 8-inch or larger telescopes and dark skies. The face-on orientation gives it a round, symmetrical appearance. Best observed from March through June.
History
Discovered by Pierre Mechain on March 15, 1781. Charles Messier cataloged it on April 13, 1781. In 1994, the Hubble Space Telescope measured Cepheid variables in M100 as part of the Key Project to determine the Hubble Constant — the expansion rate of the universe.
Fun Facts
M100 played a key role in determining the expansion rate of the universe. Hubble Space Telescope observations of Cepheid variable stars in M100 provided one of the most precise distance measurements to the Virgo Cluster, helping pin down the Hubble Constant. Five supernovae have been observed in M100 (1901, 1914, 1959, 1979, 2006).
Community Photos (1)
Credit: ESO. License: CC BY 4.0. (Wikimedia Commons)
Skybred Feb 28, 2026