The Night Sky: June 2010

Contents

The Night Sky in June 2010

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

Moon’s Phases
New Moon on the 12thFull "Strawberry Moon" on 26th                            

Stars and Constellations

Although summer officially begins this month, the stars of spring are still viewable during the early evening, including blue-white Regulus in the constellation Leo.  Regulus stands high in the southwest in early evening, and sets around midnight.  A star with similar color and brightness is Spica, which stands about halfway up in the south shortly after nightfall.  But the first true star to be spotted through the evening twilight is Arcturus, the fourth brightest star in the entire sky, in the constellation of Boötes, the Herdsman.  Arcturus has a distinct yellow-orange color, and lies high above Spica in the south at around 9 pm EDT.  To find Arcturus and Spica, first locate the Big Dipper, and follow the arc of the Dipper’s handle outward until you encounter Arcturus, then continue on to meet Spica.

 To the east of Virgo is the next zodiac constellation Libra (the Scales).  Its two brightest stars are Zubenelgenubi  and Zubeneschamali, the latter of which appears to have a greenish tinge when seen through a telescope.  If the sky is especially dark where you live, try to locate the semicircle of stars representing the constellation Corona Borealis (Northern Crown) just a bit above and to the east of Arcturus.  In mythology, Corona Borealis represented the crown of Princess Ariadne, daughter of King Minos of Crete.  The crown’s brightest star is blue-white Alphekka, also known as Gemma. To the east of Corona Borealis is Hercules, the fifth largest constellation in the sky.  The brightest star in Hercules is Rasalgethi, which is both a variable star and a double star.

One of the least known spring constellations is Canes Venatici (Hunting Dogs), which passes nearly overhead in the early evening hours of June.  This tiny group was originally part of Ursa Major, but in 1690 Johannes Hevelius introduced it to represent a faithful pair of dogs to accompany Boötes. Canes Venatici contains only one relatively bright star, Alpha Canum Venaticorum, better known as Cor Caroli, or "Heart of Charles."  The name may have been bestowed by Edmond Halley in the late 1600s in honor of his king, Charles II.  When viewed through a telescope, Cor Caroli is revealed to be a splendid double star, with the brighter component blue and the fainter one yellow.  The blue star is peculiar, showing evidence of a powerful magnetic field.  Cor Carolis is important enough to be listed in astronomer Dr. James Kaler’s book, The Hundred Greatest Stars (New York: Copernicus Books, 2002). The system lies about 110 light years from our solar system. 

Each June the Sun passes in front of the stars of Taurus and Gemini, and so these constellations are too overwhelmed by solar glare to be seen at this time of year.  The Sun reaches the solstice point on the 21st at 7:28 am, when the North Pole of Earth is tilted maximally toward the Sun, marking the beginning of summer in the Northern Hemisphere. 
 

Naked-Eye Planets In the Evening and Morning Sky 

Venus easily outshines all the other planets.  It sparkles like a yellow diamond in the west-northwest during the early evening hours. Throughout June, Venus sets roughly two and a half hours after sunset, or at 11 pm EDT, which is about as late as it can set.  Mars begins the month just to the west of Regulus, but it is moving steadily eastward, and passes just above Regulus on the 7th.  By month’s end Mars stands well to the east of Regulus. The color contrast between the orange planet and the blue-white star is quite striking.  Mars remains in view until after midnight for most of the month, setting around 1 am on the 1st and by about 11:30 pm on the 30th.    

Saturn continues to inhabit the constellation Virgo near its western border with Leo.  Saturn resembles a yellow star situated between the blue-white true stars Regulus to its right and Spica to its left.  Both Mars and Saturn have been steadily diminishing in brightness since their respective oppositions with the Sun back in January and March, although Mars has faded more dramatically and is now slightly fainter than Saturn.   Saturn remains in good position for viewing for the entire month of June, setting around 2:30 am on the 1st and by 12:30 am at month’s end.

Situated in the early morning sky, Jupiter rises by 2:30 am as June begins and around 12:30 am as the month closes.   After Jupiter has cleared the horizon, it looks like an extremely bright cream-colored star hovering low in  the eastern sky.  Also in the morning, Mercury rises about an hour before sunrise as June begins, but it will be quite a challenge to spot it against the glare of the dawn twilight.  Moreover, if your eastern horizon is obstructed by houses or trees, you will have little hope of seeing Mercury.  Toward the end of the month, Mercury sinks toward the morning twilight, and reaches superior conjunction with the Sun (i.e., Mercury lies on the opposite side of the Sun from Earth) on the 28th; it will reappear in the evening sky a few days afterwards.

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.