Stars over Sisters

May is a great month to view the constellation of Ursa Major.

Located near the north celestial pole, this collection of stars is one of only a handful of circumpolar constellations that can be seen from our latitude. A circumpolar constellation never sets and is visible year-round as it rotates counterclockwise around the North Star.

The easiest way to find Ursa Major this time of year is to look nearly overhead for its familiar asterism, the Big Dipper. Two stars at the end of the dipper's bowl are commonly used to locate the North Star.

According to legend, Ursa Major was once known as Callisto, a young woman who was an apprentice to Artimis, goddess of the hunt. Zeus, king of the gods, fell in love with Callisto, and one day when she was separated from her hunting party, Zeus took the opportunity to seduce her.

From this encounter, Callisto eventually gave birth to their son, Arcus, whom she trained as a hunter. Upon discovering her husband's infidelity, Zeus' wife Hera transformed Callisto into a bear and put her in front of Arcus who was out hunting. Before Arcus could shoot his mother, Zeus snatched the pair up and placed them among the stars, where his wife couldn't get to them.

To this day both Callisto and Arcus are safe from Hera's jealousy as they live among the stars as Ursa Major and Ursa Minor.

One of finest examples of a face-on galaxy is found in Ursa Major. Known as the Pinwheel galaxy, this vast collection of stars is located some 21-million light-years from Earth. A bright supernova occurred in this galaxy last August, and several local amateur astronomers were able to see it with their telescopes.

The month of May is also host to an annular solar eclipse. An annular eclipse happens when the moon is at its farthest distance from the earth as it passes in front of the sun. Because the apparent size of the moon isn't quite big enough to completely cover the sun, the result is a ring of light that surrounds the dark moon. The eclipse will begin at 5:08 p.m. PDT on Sunday, May 20. It will only be a partial eclipse here in Central Oregon, when at 6:24 p.m. the eclipse reaches its maximum, obscuring about 83 percent of the sun's surface.

The planets Mars in Leo and Saturn in Virgo will still be well up in the evening sky in May. The planet Venus still shines like a beacon in the west, but is gradually moving toward the sun and will be low in the sky by month's end.

The month begins with a waxing moon that becomes full on May 5. Seven days later, at last quarter, only half of the moon's surface is lit. The moon is new on May 20 as it eclipses the sun; first quarter occurs on May 28.