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The Night Sky of May

Dr. Wayne Wooten
Professor of Astronomy

For May 2015, the Full Moon, the Rose or Strawberry Moon, occurs on May 4th. The following evening, the waning gibbous moon passes two degrees north of Saturn in SE sky. The moon is last quarter on the morning of May 11th, rising about midnight. On May 18th, the moon is new. The next evening, the waxing crescent moon passes 6 degrees south of Mercury, low in the SW twilight. On May 21st, the crescent moon sits eight degrees south of Venus, well up in the SW sky. The moon is first quarter on May 25th, passing five degrees south of Jupiter overhead.

Mercury comes into the evening sky early in May, with its greatest eastern elongation on May 7th. Venus still dominates the evening sky, far brighter than any other planet. Mars is lost in the sunís glare for the next several weeks. Jupiter is still well placed of early evening sky in Cancer, just east of Regulus in Leo. This is the month for Saturn, which comes to opposition on May 25th, rising in the east in the claws of Scorpius at sunset.

The winter constellations will soon be swallowed up in the Sunís glare, but Orion is still visible, with its famed Orion Nebula, M-42, seen below the three stars marking his famed belt. Dominating the southwest is the Dog Star, Sirius, brightest star of the night sky. When Sirius vanishes into the Sunís glare in two months, this sets the period as "Dog Days".

The brightest star in the NW is Capella, distinctively yellow in color. It is a giant star, almost exactly the same temperature as our Sun, but about 100X more luminous. Just south of it are the stellar twins, the Gemini, with Castor closer to Capella, and Pollux closer to the Little Dog Star, Procyon.

Overhead, the Big Dipper rides high. Good scouts know to take its leading pointers north to Polaris, the famed Pole Star. For us, it sits 30 degrees (our latitude) high in the north, while the rotating earth beneath makes all the other celestial bodies spin around it from east to west. If you drop south from the bowl of the Big Dipper, Leo the Lion rides high. Note the Egyptian Sphinx is based on the shape of this Lion in the sky.

Taking the arc in the Dipperís handle, we "arc" SE to bright orange Arcturus, the brightest star of spring. Cooler than our yellow Sun, and much poorer in heavy elements, some believe its strange motion reveals it to be an invading star from another smaller galaxy, now colliding with the Milky Way in Sagittarius in the summer sky. Moving almost perpendicular to the plane of our Milky Way, Arcturus was the first star in the sky where its proper motion across the historic sky was noted, by Edmund Halley. Just east of Arcturus is Corona Borealis, the "northern crown", a shapley Coronet that Miss America would gladly don, and one of few constellations that look like their name. The bright star in the crownís center is Gemma, the Gem Star.

Spike south to Spica, the hot blue star in Virgo, then curve to Corvus the Crow, a four sided grouping. The arms of Virgo harbor the Virgo Supercluster of Galaxies, with thousands of "island universe" in the Spring sky.

To the northeast Hercules rises, with his body looking like a butterfly. It contains one of the skyís showpieces, M-13, the globular cluster faintly visible with the naked eye. Find it with binoculars midway on the top left wing of the cosmic butterfly, then take a look with a larger telescope and you will find it resolved into thousands of stars!

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