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Starwatch May 2012

April 20, 2012

Colliding galaxies.

Known as "the Bird" or "Tinkerbell," this stunning and rare triple merger of galaxies took place some 650 million light-years away. The wings extend 100,000 light-years, comparable to the diameter of the Milky Way. Image: ESO

By Deane Morrison

May is full of delights, starting with a full moon on the 5th.

This moon, known to Algonquin Indians as the flower moon, milk moon or corn planting moon, rises only about two hours before the moment of perfect fullness, which comes at 10:35 p.m. Not only that, but the moon will be at perigee—its closest approach to Earth in its orbit—only three minutes before fullness, so it will be not only round but big, although the size difference may well be imperceptible.

Venus is busy this month taking a spectacular plunge into the sun's afterglow. Through a small telescope or even a pair of steady binoculars, you can see the planet's crescent shape as it wanes away. On June 5, Venus will make a rare passage right across the face of the sun.

Mars and Saturn are front and center in the south after nightfall. Mars is higher and in the south-southwest. Just to the northwest of Mars is Regulus, the brightest star in Leo. Saturn, in the south-southeast, is also paired with a bright star; its companion, shining just below the planet, is Spica, in Virgo. High above Saturn and Spica is Arcturus, the brilliant beacon in Bootes, the herdsman.

On the 20th, we're treated to a partial eclipse of the sun. The show begins at 7:20 p.m., and the sun will set while still in a state of partial eclipse. A little more than half its surface will be covered by the moon. The usual warnings about solar eclipses apply: Do not look at the sun without proper protection. If you're unsure—don't look. The safest way to view a solar eclipse is with a pinhole camera—or on TV.

Whether partial or total, solar eclipses always occur at the time of a new moon, when the moon is gliding between Earth and the sun. Usually, the moon passes either north or south of the sun. But since the orbits of the Earth around the sun and the moon around the Earth aren't aligned, their paths cross; the intersections are called nodes. Solar eclipses happen when a new moon crosses a node. When a full moon does, we get a lunar eclipse.

If skies are dark, see if you can make out the star pattern called Three Leaps of the Gazelle. It comprises three evenly spaced pairs of stars between the bowl of the Big Dipper and the curved Sickle of stars outlining Leo's head.

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:

Twin Cities, Minnesota Institute for Astrophysics (during fall and spring semesters):

4/20/12 Contact: Deane Morrison, University Relations, (612) 624-2346,

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Star map: White on black

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