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The Night Sky of May

Dr. Wayne Wooten
Professor of Astronomy

For May, the moon is full on April 29th, so the first two weeks of May find it waning in the morning sky. The waning gibbous moon passes two degrees north of Saturn on May 4th, and three degrees north of Mars on May 6th. It is last quarter on May 7th. The new moon occurs on May 15th. The waxing crescent moon passes five degrees south of bright Venus on the evening of May 17th. The first quarter moon is on May 21st, and the waxing gibbous moon passes four degrees north of Jupiter on May 27th. The full moon, the flower moon, occurs on May 29th. On the 31st, the waning gibbous moon again passes 1.6 degrees north of Saturn, both rising about 10 p.m. in SE.

Mercury is in the morning sky early this month, but disappears in the sun’s glare by the 10th. Venus dominates the evening sky in the SW, and appears as a featureless brilliant gibbous disk in the telescope. Mars in still in the morning sky, but as the faster earth overtakes it at opposition on July 27th, is getting bigger and brighter each day. Jupiter is spectacular in the SE evening sky now, reaching opposition in early May in Libra. Be sure to check out the four large Galilean moons with small telescopes, arrayed in a line around Jupiter’s equator. All except Callisto can pass in front of Jupiter and cast shadows.

This is a good month for Saturn as well, which comes to opposition on June 27th, rising in the east in Sagittarius. Good telescopes Saturn with its rings about as open as they can appear in the telescope. You can also see Titan, Saturn’s biggest moon, in small telescopes easily.

The winter constellations will soon be swallowed up in the Sun’s 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 Sun’s 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 Dipper’s 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 shapely Coronet that Miss America would gladly don, and one of few constellations that look like their name. The bright star in the crown’s 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. Note Jupiter now near Spica. 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 sky’s 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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