The Night Sky: May 2010

Contents

The Night Sky in May 2010

By Harry J. Augensen
Professor of Physics & Astronomy, Widener University

Moon’s Phases
New Moon on the 13thFull "Flower Moon" on 27th                            

Stars and Constellations

Starlit nights in May are often pleasantly cool, with just a light jacket required for outdoor viewing.  But with the Sun setting around 8 pm or later during the month, you will need to wait until close to 9 pm for the sky to get dark enough to make out the constellations.   Get a last look at Aldebaran and the Pleiades star cluster, Rigel and Betelgeuse, Pollux and Castor, and Sirius and Procyon.  Bright yellow Capella is setting in the northwest, but will still be visible through June.  These bright stars of winter are all fading into the evening twilight, not to reappear in the night sky until autumn.

 The celestial stage now belongs to the stars of spring.  Regulus in Leo is high in the southeast, and another fairly bright star, Alphard, in the constellation Hydra, the Water Snake, is now rising, a bit below Regulus.  If you wait until after 10 pm, you will see yet another bright star, Spica, in the constellation Virgo, rising in the southeast.  The Big Dipper, which is part of the constellation Ursa Major, is now rising in the northeast, and its famous "pointer stars" point to Polaris, the North Star.  The handle of the Dipper arcs to Arcturus, the bright yellow-orange star in the constellation Boötes, the Herdsman, which is rising in the east.  Mizar, the second star from the end of the Big Dipper’s handle, is actually a multiple system. As a test of vision, see if you can spot Mizar’s faint companion star, Alcor.

One of the largest and most spectacular constellations in the night sky at this time of year is Centaurus (Chiron in Greek mythology) but only the uppermost portions of this group can be glimpsed from latitudes north of the Gulf Coast states.  Centaurus lies just below the tail end of Hydra, and skims the southern horizon around midnight in May.  Like Orion, Centaurus boasts two first-magnitude stars: alpha and beta Centauri.  Alpha Centauri, also known as Rigel Kentaurus, is a triple-star system, and has the distinction of being our Sun’s nearest stellar neighbor, at a distance of 4.3 light years.  Even more interesting is that the brightest of the three components, alpha Centauri A, is nearly identical in chemical composition and intrinsic brightness to the Sun.  Beta Centauri, by contrast, is a blue-white giant star many times larger than the Sun and it lies much farther away than alpha, around 200 light years.  If your travels take you to Mexico, Hawaii, or, even better, South America, southern Africa, Australia, or New Zealand, watch for brilliant Centaurus in the night sky in May.

Naked-Eye Planets In the Evening and Morning Sky 

There is no mistaking the planet Venus, which looks like a magnificent yellow diamond hovering above the western horizon during the early evening hours of May.  Throughout the entire month, Venus remains visible during the evening for a generous amount of time, setting around two and a half hours after sunset, or at about 10:15 pm EDT on the 1st and by 11 pm on the 31st.

 Mars continues to shine like a bright, copper-colored star just to the west of Regulus in Leo.  Mars remains in view until well after midnight, setting around 2:30 am on the 1st and by about 1 am on the 31st.   Mars’ distance from Earth has more than doubled since its opposition with the Sun back in January, and its brightness has faded by nearly a factor of ten.  Saturn, now located in the western part of the constellation Virgo, near the border with Leo, resembles a yellow star situated roughly between the (true) blue-white stars Regulus  to its upper right and Spica to its lower left.  Saturn’s brightness has faded since its opposition with the Sun back in March, and it is now about equal with that of nearby Mars.  Saturn remains in good position for viewing for nearly the entire month of May, setting during the very early hours of morning.

Jupiter begins to emerge from the dawn twilight during May, rising about 4 am EDT (roughly two hours before sunrise) at the beginning of the month and by 2:30 am on the 31st.   Allow Jupiter an hour or so to clear the horizon after it rises, and you will easily spot it looking like a bright cream-colored star.  Mercury reached inferior conjunction with the Sun late last month, and is therefore be unobservable until very late in May, when it appears low above the eastern horizon before the Sun rises. Mercury reaches greatest elongation on the 26th, rising about an hour before sunrise, but it will be a challenge to spot it against the glare of the dawn sky.

For more information on astronomy and weather, visit the Widener University Public Viewing Website at http://www.widener.edu/stargazing/, then click on Web Links & Resources. A set of free sky maps can be obtained at http://www.skymaps.com/

Some content for this article has been obtained from US Naval Observatory Data Services

Times given apply for observers near to the latitude and longitude of Philadelphia, USA: 40 degrees North latitude, 75 degrees West longitude.