May's night skies

by Rich Heffern

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The warmer nights of May are prime conditions for galaxy hunting. The winter Milky Way is lost in the glare of the Sun. On these evenings we have an unobstructed view of what lies beyond our own galaxy as the night skies present us with a vista outside the Milky Way. At the center of this view, we find the constellation Virgo, a large constellation, second in size to Hydra.

The draw to Virgo for astronomers of all stripes is the Virgo Galaxy Cluster, which spills across its northern border into the constellation Coma Berenices. A neighbor to our own Local Group of galaxies, 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 3,000 galaxies, centered on the giant elliptical galaxy M 87, which is visible as a 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 degrees northwest of the star Rho Virginis. At low power in a telescope, 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.

On spring evenings the Big Dipper turns over as if to dump spring rains on the world, or so it appears to Northern Hemisphere sky watchers. Look for the Dipper very high in the northeast as the stars come out.

The planet Saturn is visible until mid-July, also in the sky near the constellation Virgo.

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