The warm nights of June offer prime conditions for galaxy hunting. The winter Milky Way is lost in the glare of the Sun, while the star clouds of Cygnus and Sagittarius are just rising in the east. It is on these evenings that we have an unobstructed view of what lies beyond our own galaxy. At the center of this view, we find the constellation Virgo.
Virgo is a large constellation, second in size to Hydra and spanning more than 1295°. Despite its large size Virgo is not a particularly prominent constellation, with the notable exception of silver-blue Spica, magnitude +1. Spica is over twice as hot as Sirius (the brightest star in the night sky) and 100 times more luminous. However, Spica appears fainter than Sirius because of its considerably greater distance, 270 light-years.
The primary telescopic draw to Virgo is the Virgo Galaxy Cluster, which spills across its northern border in Coma Berenices. A neighbor to our own Local Group, the Virgo Cluster is the richest gathering of galaxies in the Local Supercluster – a large group of associated small galaxy clusters that include the Local Group and therefore our own galaxy, the Milky Way.
The Virgo Galaxy Cluster contains about 3000 galaxies, centered on the giant elliptical galaxy M 87, which is visible as a 9th-magnitude smudge in small telescopes or even binoculars. M 87 has a total mass of nearly 800 billion suns, making it one of the most massive galaxies known. Long-exposure photographs show a jet of luminous gas being shot out of M 87, as though the galaxy has suffered a violent event. Astronomers now believe that the activity in M 87 is due to a black hole with a mass of three billion suns, which lurks in the galaxy’s nucleus.
M 87 is easily located in northern Virgo, about 3° northwest of the 5th-magnitude star Rho Virginis. At low power, the 8.6-magnitude galaxy resembles an unresolved globular cluster, about 3′ across and perfectly round. A very bright core, one-third of the galaxy’s overall size, blazes in the center.
Finder map – field width 15 degrees, stars to magnitude +9.