The Night Sky: May 2013

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The Night Sky in May 2013

By Harry J. Augensen

Professor of Physics & Astronomy, Widener University

Moon’s Phases
New Moon on the 9th       Full "Flower Moon" on the 25th

Stars and Constellations

May is often associated with a plethora of tree and shrub blossoms such as dogwood, cherry, and lilac on the terrestrial landscape, while the celestial sphere this month is also "blooming" with stars and planets.  Early in the month as darkness falls (around 8:30 pm EST), you may be able to catch a last look at Aldebaran (near Jupiter), Betelgeuse, Sirius, and Procyon.  These bright stars of winter are all fading into the early evening twilight, and will reappear in the night sky next autumn.  Pollux, Castor, and Capella are getting low in the northwest, but because of their high northern declinations you will still be able to see them through at least early June.

The stars of spring are now the undisputed rulers of the evening sky.  Regulus, the brightest star in Leo, the Lion, is high in the south, followed by Spica, or Alpha Virginis, which after about 10 pm should be well up in the southeast.  But the brightest of the spring stars is Arcturus, the yellow-orange star in the constellation Boötes, the Herdsman, which is high in the east-southeast. Arcturus is easily found by following the arc of the Big Dipper's handle. The Big Dipper, which is part of the constellation Ursa Major, is now rising in the northeast, and its pointer stars Merak and Dubhe, point to Polaris, the North Star.

Regulus, Spica, and Arcturus form the  "Spring Triangle," with the right angle at Spica.  Though not as famous as the soon-to-rise Summer Triangle (consisting of Vega, Altair and Deneb), the  Spring Triangle is larger and is fairly easy to discern during the evening hours of May.  An interesting fact is that during the months of spring, the three brightest stars in the northern skies, each representing a different season – yellow-white Capella (winter), orange-yellow Arcturus (spring), and blue-white Vega (summer) – can all be seen on the same night at the proper time of night.  That night occurs during the middle of May, at around 10 pm, when Capella is setting, low in the northwest, while Vega is in the opposite part of the sky, rising in the northeast, and Arcturus is ideally situated nearly overhead.

 It is worth pointing out that of the 88 existing constellations, the three largest (i.e., that cover the largest area in square degrees) can be found in the spring sky:  Hydra, Virgo, and Ursa Major.  Hydra (the Water Snake) has the distinction of being the largest of all the constellations, although most of its stars are pretty faint. According to British astronomer Chris Kitchin, Hydra dates back to at least the time of Ptolemy’s Almagest in 145 AD, but may go back even further to the ancient Babylonians (2000 BC). In Greek mythology, Hydra was a multi-headed serpent which haunted the river Amymone, and was eventually slain by Hercules as one of his twelve labors.   Hydra winds across the southern sky on spring nights, and its brightest star, orange Alphard, lies a bit below Regulus.  Alphard, which means the "solitary one," is appropriately situated in a region of the sky which contains almost no other nearby stars of comparable brightness.  Alphard, like Arcturus, is an orange giant star, but lies about five times further from our solar system and hence looks much dimmer.

Two other faint constellations that are nearby but often get little attention are Corvus (the Crow), and Crater (the Cup).  Both belong to Ptolemy’s original 48 constellations of two millennia ago, and both lie just above the tail of Hydra.  According to sky lore, the god Apollo gave a cup to a crow with instructions to fetch water from a river.  The crow dawdled too long, and when it returned the angry Apollo threw both the crow and the cup into the heavens near the Hydra.


Naked-Eye Planets In the Evening and Morning Sky

After having reached superior conjunction with the Sun in late March and spent nearly all of April lost in the solar glare, Venus gradually begins to emerge from the evening twilight in the second half of May.  Sharp-eyed observers will be able to spot it low above the western horizon shortly after sunset, so long as trees and houses do not block the view.  In fact, toward the end of May, Venus, Jupiter and Mercury will all reside in the same general region of the sky low above the northwestern horizon 30 minutes to an hour after sunset, and the (apparent) interactions between them will be fascinating to watch.

Jupiter resembles a brilliant golden star low in the west during the first hour or two after sunset, but it is slowly getting lower in west-northwest with each passing night.  Jupiter stands above and to the left of Aldebaran in the constellation Taurus. Jupiter sets by just before 11 pm EDT (just under three hours after the Sun) on the 1st, and by just before 8:30 pm at month's end.  As Jupiter sinks night by night toward the horizon, it passes first Mercury and then Venus which are on their way up.   

For the first half of May, Mercury lies in the morning sky, but is lost in the glare of the Sun.  By midmonth, however, Mercury swings into the evening sky, and can be spotted low above the horizon in the early morning hours.  Look toward the east about 30 minutes before sunrise, but binoculars or a telescope may be needed, and trees may block the view.  Toward the end of the month, Mercury climbs to a significant height above the horizon and joins Jupiter and Venus to form a beautiful trio hovering low above the northeastern horizon about a half hour or so after sunset.

Saturn reached opposition with the Sun in late April, at which time it was closest to Earth and also up all night long.  As darkness falls at the start of May, Saturn continues to be in excellent position for viewing, and can be seen rising low in the southeast.   Saturn resembles a bright, cream-colored star in the western portion of the constellation Libra, near the border with Virgo.  As the month progresses, Saturn moves westward, crossing the Libra-Virgo border in the middle of the month and continuing its westward (retrograde) trek into Virgo,  eventually winding up to the lower left of Virgo's brightest star, Spica. 

Mars was in conjunction with the Sun last month, and is still unobservable.

The Sun begins the month of May within the borders of the zodiac constellation Aries, then crosses into neighboring Taurus on the 13th.


Information on lunar phases and rise/set times of Sun and planets is obtained from the US Naval Observatory Data Services at Additional information comes from Astronomical Calendar 2013 by Guy Ottewell (Raynham, MA: Universal Workshop, 2013)Times given apply for observers near to the latitude and longitude of Philadelphia, USA: 40 degrees North latitude, 75 degrees West longitude.

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Augensen, H. (2013). The Night Sky: May 2013. Retrieved from