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The Night Sky of May

Dr. Wayne Wooten
Professor of Astronomy

For May 2017, the moon is first quarter on May 2nd. The waxing gibbous moon passes two degrees north of Jupiter in the SE twilight sky on May 7th. The full moon, the Rose or Strawberry Moon, is on May 10th. The waning gibbous moon passes three degrees north of Saturn, both rising about 10 PM, on May 13th. The moon is last quarter and rises about midnight on May 18th. The waning crescent passes two degrees south of brilliant Venus in the dawn sky on May 22nd. The new moon is on May 25th, and there are only three more new moons until the total solar eclipse on August 21st!

Mercury is in the morning sky this month, and reaches greatest western elongation on May17th, some 26 degrees to the right of the rising sun. Venus is also in the dawn sky, but much brighter. Look for the crescent moon in the morning daytime sky on May 22nd, and look just above it to catch Venus in broad daylight with your eyes alone. Mars in low in the southwest after sunset, getting lost in the sunís glare by monthís end. But Jupiter is spectacular in the SE evening sky now, reaching opposition in early April. Be sure to check out the four large Galilean moons with small telescopes, arrayed in a line around Jupiterís equator. The bright star Spica of Virgo is just to the lower right of it presently. This is a good month for Saturn as well, which comes to opposition on June 15th, rising in the east on the Scorpius-Sagittarius border. Good telescopes Saturn with its rings about as open as they can appear in the telescope. You can also see Titan, Saturnís biggest moon, in small telescopes easily.

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, the 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. 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 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! This monthís featured photo shows the way this fine cluster can be resolved visually in scopes about 8" in aperture. The bigger the scope, the more stars!

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