Galaxies M98, M99, and M100 are part of the Virgo Galaxy Cluster, a collection of more than a thousand galaxies that forms the heart of the Local Supercluster of galaxies. It is sometimes also called the Virgo-Coma Cluster. Galaxy M100, at upper left, is a grand-design spiral galaxy. It is also one of the brightest galaxies in the Virgo Cluster at a visual magnitude of 9.3. It has an apparent size of 6 x 7 arc minutes. It lies at a distance of about 50 million light years and contains more than 100 billion stars. The Hubble Space Telescope's study of Cepheid variable stars in M100 led to the first reliable distance measurement of a galaxy in the Virgo Cluster. Galaxy M99, at bottom center, is a 9.9 magnitude spiral galaxy with an apparent size of 5 x 5 arc minutes. Galaxy M98, at right, is a 10th magnitude spiral with an apparent size of 3 x 9 arc minutes. Pierre Mechain discovered M100 and M99 on March 15, 1781, and then M98 on March 17 of the same year.