The Night Sky: June 2009

Contents

The Night Sky in June 2009

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

Moon’s Phases in Month
  Full "Strawberry" Moon on the 7thNew Moon on the 22nd

Stars and Constellations

The stars of spring remain quite prominent during June evenings, and the first star to poke through the evening twilight is Arcturus, the night sky's fourth brightest star, in the constellation of Boötes, the Herdsman.  Arcturus has a distinct yellow-orange tinge, and by around 9 pm EDT lies high in the south. Also easily found is bluish-white Regulus in the constellation Leo, the Lion.  Regulus stands high in the southwest in early evening, and sets around midnight.  A star with nearly the same color and brightness as Regulus is Spica, in Virgo, which stands below Arcturus, about halfway up in the south shortly after nightfall.  Regulus, Spica, and Arcturus form the "Spring Triangle," which, though not as famous as its summer counterpart, is nonetheless a noteworthy sight.

Later in the evening, as the stars of spring migrate toward the western horizon, the stars of summer begin to take center stage.  One of the most famous of these is blue-white Vega, in the constellation Lyra, which can be seen rising in the northeast.  Another is reddish Antares, in Scorpius, which is low in the southeast.  In mid-June, Antares rises around 7:30 pm EDT (before sunset) and crosses the south meridian just before midnight. Lying between Virgo and Scorpius is the constellation Libra, the Balances, which contains no first magnitude stars.

Leo, Virgo, Libra, and Scorpius are all zodiac constellations, through which the Sun "appears" to pass at some time during the year.  Specifically, the Sun passes through Leo from August 10 to September 15, Virgo from September 16 to October 30, Libra from October 31 to November 22, and Scorpius from November 23 to 29.  These constellations are naturally best visible in the night sky at the opposite time of the year from when the Sun is located in them.  Also note that these time intervals are roughly one month off from when the astrological signs of the same name are supposedly in effect, a direct result of precession of Earth’s axis over the two thousand years since ancient astrologers conjured up their pseudoscience.

It is during the month of June that the Earth, traveling in its orbit about the Sun, reaches the summer solstice point, where the Northern Hemisphere is tilted maximally toward the Sun.  This event occurs in 2009 on June 21st at 1:45 am EDT, and marks the beginning of astronomical summer in the Northern Hemisphere. The Southern Hemisphere is simultaneously tilted away from the Sun, thus marking the start of winter for those folks.  The politically correct designation is hence "June solstice."  From an Earth-bound observer's point of view, the noon Sun appears higher in the sky at this time than at any other time of the year.  For regions north of the equator, this translates into a higher concentration of solar radiation than at any other time of the year.  At latitude 40 degrees North (New York, Philadelphia, Cleveland, Chicago, Des Moines, Omaha, and Salt Lake City are all close to this latitude), the duration of daylight reaches around 15 hours, while night is shortened to only about 9 hours. Consequently, the night sky does not become really dark until after about 9:30 pm Daylight Time.

 Naked-Eye Planets In the Evening and Morning Sky

Saturn remains in good position for viewing during the first half of the night, setting around 2 am at the beginning of June, and at midnight by month's end.  Saturn is easily spotted high in the southwest in mid-evening in the constellation Leo, resembling a bright yellow star lying to the east of Regulus, which is only slightly less bright than Saturn.  Jupiter is about 25 times brighter than Saturn, and so sky watchers will have no trouble locating it once it rises.  Jupiter looks like a brilliant cream-colored star in the faint constellation Capricornus, nearly on the opposite side of the sky from Saturn in Leo.  As June begins, Jupiter rises around 1 am, just an hour before Saturn sets.  By the end of June, Jupiter rises at 11 pm.

Mars has been a less than impressive sight thus far this year, but that will be changing in the coming months as the distance between Earth and the Red Planet continues to decrease.  Mars will be moving from the morning into the evening sky late this fall, and will reach opposition with the Sun and closest approach to Earth in late January 2010.  Right now, reddish Mars is a little less bright than Saturn, and can be seen above the eastern horizon during the early morning hours.  Mars rises at around 3:30 am at the start of June, and by about 2:30 am at month's end.  Mars passes fairly close to Venus later in the month, making for a particularly fine sight.

Venus continues to stand out as the most brilliant object (other than the Moon) in the pre-dawn sky.  Venus has actually decreased in brightness over the past two months, but not by much.  Venus officially reaches greatest elongation with the Sun on the 5th, but this will not be particularly noteworthy because of the unfavorable orientation of the ecliptic plane to the eastern horizon at dawn.  Venus rises around 3:30 am at the beginning of June, or just about 2 hours before sunrise, and by about 3 am at the end of the month.   Of note is that Venus is paired with much fainter Mars for much of June.   Mercury, like Venus, reaches greatest morning elongation during June, on the 13th.  For about the last 3 weeks of June, Mercury rises about an hour before sunrise, and can be seen resembling a bright yellow star hovering low above the east-northeast horizon in the morning twilight.

The nearly full Moon will pass in front of the star Antares on the night of the 6th, as viewed from much of the US, and especially along the East Coast.   Disappearance/reappearance times are provided for major cities at:  www.lunar-occultations.com/iota/bstar/0607antares.htm.

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.