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Starwatch April 2012

March 21, 2012


M100 Galaxy in the Virgo Cluster.

The galaxy known as M100 is one of the brightest in the Virgo Cluster. It's about 56 million light-years away, and some of its stars have been useful in determining the size and age of the Universe.

Photo: NASA

By Deane Morrison

It may be April, but 'tis the start of the fall season. The fall of Venus from the evening sky, that is.

Our sister planet begins the month about as high as it ever gets. Look about 90 minutes after sunset on the evening of April Fools Day, when the Pleiades star cluster comes out in the west just above brilliant Venus. Grab your binoculars and hope the waxing moon doesn't interfere with this beautiful pairing.

Venus begins its descent in April, but the going is slow at first. Through a telescope its phase thins from 48 percent to 27 percent lit, but its diameter and brightness increase because it's getting closer. On the 23rd and 24th, watch a young crescent moon climb past Venus. Next month the planet will drop faster, en route to a spectacular transit of the sun's face on June 5.

Earth laps Saturn in the orbital race on April 15, when the ringed planet rises in the east and stays up all night. Saturn's current companion, the bright star Spica, in Virgo, rises just west of the planet. Shining high to their upper left is Arcturus, the jewel of Bootes, the herdsman.

Virgo is famous for its rich collection of more than 1,000 galaxies, called the Virgo Cluster. It is a neighbor of the Local Group, the cluster of galaxies to which the Milky Way belongs. The Virgo Cluster has at least 20 times as many galaxies as the Local Group, and its combined gravity is so strong we are actually being drawn toward it. The Virgo Cluster isn't visible to the naked eye, but it spans five degrees of sky, an area as wide as 10 full moons.

Mars is high in the south after sunset, fading but still a ruddy beacon. Like Saturn, it's paired with a star: Regulus, the heart of Leo, just west of the planet. While you're admiring Leo, use binoculars and look west of Regulus, about halfway to the Gemini twins, to find the subdued but lovely Beehive star cluster in Cancer.

April's full moon rises the night of the 6th. This moon has been called several Algonquin Indian names: the pink moon, for the carpet of flowering ground phlox that appears in early spring; the full sprouting grass moon; the egg moon; and, in coastal areas, the full fish moon, as mid-April was the time of the shad spawning runs. It travels the night sky close to Spica and Saturn.

The Lyrid meteor shower peaks around midnight April 22. Meteors will radiate from the east, between the constellations Lyra and Hercules.

The University of Minnesota offers public viewings of the night sky at its Duluth and Twin Cities campuses. For more information and viewing schedules, see:

Duluth, Marshall W. Alworth Planetarium: www.d.umn.edu/planet

Twin Cities, Minnesota Institute for Astrophysics (during fall and spring semesters): www.astro.umn.edu/outreach/pubnight

3/21/12 Contact: Deane Morrison, University Relations, (612) 624-2346, morri029@umn.edu

Find U of M astronomers and links to the world of astronomy at http://www.astro.umn.edu.

Tags: College of Science and Engineering

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Star map: White on black

Star map: Black on white