The faint but famous constellation Hercules climbs into the sky on May evenings, and stands high in the east as night falls by the end of the month. It is marked by a four-sided figure known as the Keystone. The huge star cluster M13 perches between the Keystone's top two stars. Libra, the balance scales, climbs into view in the south, heralding the pending return of the summer constellation Scorpius.
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In the Sky This Month
May 20: Moon and Planets
Jupiter, the solar system’s largest planet, rises to the upper right of the Moon late this evening. It looks like a brilliant star. The second-ranked planet, Saturn, follows them in the wee hours of the morning, well to the lower left of the Moon.
May 21: Moon and Saturn
Look for the Moon and a bright companion the next couple of mornings. The planet Saturn will be close to the upper left of the Moon at first light tomorrow, and closer to the right of the Moon on Thursday.
May 22: Ophiuchus
Ophiuchus, the serpent bearer, wheels high across the south tonight. It’s not that much to look at — only a few modest stars climbing above the scorpion.
May 23: Changing the Guard
Some of the brightest stars of winter are dropping from the evening sky. Low in the west at nightfall, look for bright white Procyon in Canis Minor, the little dog. The “twins” of Gemini, Pollux and Castor, are well to the upper right of Procyon.
May 24: Omega Centauri
Omega Centauri contains millions of stars packed into a ball a few dozen light-years across. It is bright enough to see with the eye alone, but only from the southern third of the U.S. It is quite low in the south about 11 p.m. and looks like a fuzzy star.
May 25: Last-Quarter Moon
The Moon will be at last quarter tomorrow, indicating that it is three-quarters of the way through its monthly cycle of phases. Sunlight will illuminate half of the lunar hemisphere that faces Earth.
May 26: Guitar Nebula
Cepheus, the king, is low in the north at nightfall. The constellation’s brightest stars form a shape that resembles a child’s drawing of a house.