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The Sky of May
Dr. Wayne Wooten
Professor of Astronomy
Escambia Amateur Astronomers' Association
 For May 2008, the Moon will be
new on May 5th. The first and second full weeks of May will thus find the Moon waxing, passing just north of Mercury on May 6th, then passing just south of Mars on
May 10th, and reaching first quarter, two degrees south of Saturn, on May 12th. The full moon is on May 20th, and is called the ‘Milk Moon’ in tradition. It passes
two degrees south of Jupiter on the morning of May 24th, and is last quarter moon on May 28th. Thus the last weeks of May will be ideal for deep sky observing, with
the moon absent from the evening.
While the naked eye, dark adapted by several minutes away from any bright lights, is a wonderful instrument to stare up at the Galaxy arching
overhead, binoculars are better for spotting specific deep sky objects all along the plane of the Galaxy. For a detailed map of northern hemisphere skies, about April
30th visit www.skymaps.com website and download the map for May 2008; it will have a more extensive calendar, and list of
best objects for the naked eyes, binoculars, and scopes on the back of the map. Also available as the next month begins is wonderful video exploring the May sky,
available from the Hubble Space Telescope website at:
http://hubblesite.org/explore_astronomy/tonights_sky/.
Saturn is the brightest object overhead as darkness falls. Its rings are closing now, and will vanish edge-on at its 2010 equinox. If the
image is steady, look for the split in the two bright rings, the Cassini division, and the fainter crepe ring closer to the planet than the bright A and B rings. You
may also see some belts and zones on the planet’s disk. The largest, Titan,
will be seen in any small telescope, but others will need larger scopes to spot. To the west, Mercury puts on a nice display in the first two weeks of May. It passes
the Pleiades cluster on May 2nd, is joined by the Moon on May 6th, and is at its highest in the evening sky at greatest eastern elongation on May 14, some 22 degrees
from the setting Sun, about as good as it gets for Earth based observers. But it rapidly retrogrades between us and the Sun in the next week, to vanish in solar glare
by the 20th; it was not named for the speedy messenger god for nothing!
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. Below it is a fine open cluster,
M-41, easily spotted in binoculars. 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.
Mars starts the month just south of the pair, but moves eastward into adjacent Cancer by month’s end, moving through the fine Beehive cluster, M-44, a great binocular
target, on May 23rd.
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. Just north of the
Great Bear’s nose is this month’s featured photo by Bob Gaskin. The colliding pair of galaxies, M81 and M-82, are visible with binoculars on dark clear nights high
overhead, and while larger M-81 appears an almost normal spiral, M-82 is a starburst galaxy, the collision setting off waves of rapid star formation and blowing much
gas and dust into space.
If you drop south from the bowl of the Big Dipper, Leo the Lion rides high. Saturn lies just east of the bright star Regulus, the heart of the
King of Beasts. 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 its 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. It is above Corvus, in the arms of Virgo, where our large scopes will show members of the Virgo Supercluster, a swarm of over a thousand galaxies about 50 million light years away from us.
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