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The Night Sky of May

Dr. Wayne Wooten
Professor of Astronomy

For May 2016, the moon is new on May 6, and at first quarter on May 13th. The waxing gibbous moon passes 2 degrees south of Jupiter on May 19th The Full Moon, the Rose or Strawberry Moon, occurs on May 21s, with the moon 6 degrees north of Mars, which is at opposition the following evening. The following evening, the waning gibbous moon passes three degrees north of Saturn in SE sky. The moon is last quarter on the morning of May 29th, rising about midnight. 

Mercury passes directly between Earth and Sun on the morning of Monday, May 9th. This transit that will start locally about 6 AM sunrise, and end about 1:30 PM with Mercury leaving the sun’s disk. Note the tiny round sharp disk of Mercury is much smaller than the larger but les distinct sunspot; this sunspot was about as big as our own planet Earth.

Venus is moving behind the sun, from the morning into the evening sky, and thus lost in its glare now. But Mars is being overtaken by the earth, and dominates the SE evening sky with its red color. It comes to opposition on May 22nd, and is closest to Earth, almost exactly half the earth-sun distance, at month’s end. This is the best view of the red planet we have had this decade, so enjoy it the next few weeks, before we leave it behind and it fades and shrinks in the scopes. Jupiter is still well placed up in the eastern early evening sky, just south of the tail of Leo. This is a good month for Saturn as well, which comes to opposition on June 3rd, rising in the east just north of Antares in Scorpius at sunset. 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 shapley 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. 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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