The Night Sky: August 2008

The Night Sky in August, 2008 

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

Moons Phases in August
New Moon on the 1stFull "Sturgeon" Moon on the 16th

Stars and Constellations
As darkness falls on clear August evenings, the first star to appear is orange-yellow Arcturus, which stands high in the west about an hour or so after sunset. This identification can be verified once it gets dark enough to locate the Big Dipper, a part of the constellation Ursa Major, which is beginning to dip into the northwest. The two bright stars in the front of the Dipper, Merak and Dubhe, point to Polaris, the North Star, while the arc of the Big Dippers handle leads to Arcturus. If the sky is dark enough, you may be able to see the Little Dipper, which is part of Ursa Minor, extending outward from Polaris toward the upper left. Try also to make out the large, but faint summer constellation Draco, which winds across the sky high above the Little Dipper. Draco represents the mythological dragon that guarded the golden apples in the Garden of the Hesperides. As one of his twelve labors, Hercules slew the dragon and made off with the apples. Draco is especially notable because one of its stars, Thuban, was the polestar some 4000 years ago.

You may be able get one last glimpse of the spring star Spica as it sets in the southwest. To the far left of Spica is orange-red Antares in Scorpius, the Scorpion, which is visible low in the south-southwest. The body of the Scorpion snakes down toward the horizon and then upward into a curved stinger. Look closely, and you will see the cats eyes, a pair of stars located at the end of the tail which seem to be winking at you. Shaula is the left and brighter of the two stars, while Lesath is the fainter one on the right. To the upper left of the cats eyes is the teapot of Sagittarius, an easy grouping to identify. The teapot marks the general direction of the center of our Milky Way galaxy. If you live away from city lights, you can make out the Milky Way as a hazy band stretching across the sky from southwest to northeast. In fact it passes through the region of the summer triangle, which at this time stands high in the east-northeast. The triangle is comprised of Vega in the constellation Lyra (the Harp), Deneb in Cygnus (the Swan), and Altair in Aquila (the Eagle). About halfway between Vega and Altair is the moderately bright star Albireo, also known as beta Cygni. A telescope reveals that this star is actually two stars, one yellow and the other blue. The color of a star indicates its surface temperature: blue stars are the hottest (upwards of 20,000 °F), white stars are less so (15,000 °F), yellow stars like the Sun are moderately cool (11,000 °F), and red stars like Antares are the coolest (6000 °F or less). All three stars of the summer triangle are whitish in color, indicating that they are all somewhat hotter than our Sun.

On August evenings you should be able to distinguish the W shaped constellation Cassiopeia as it rises low in the northeast. Late in the evening the Great Square of Pegasus, which consists of four stars in the form of a rectangle lying on its edge, can be seen rising in the east. These are two signs that autumn is just around the corner!

Planets
Mercury is lost in the evening twilight in early August, but by mid-month it has risen high enough to be seen low in the northeast within an hour or so after sunset. Also in mid-August, Mercury passes close (apparently) to Saturn and a few days later Venus. Speaking of Venus, it is beginning to make a gradual reappearance in the evening sky, but you will need an unobstructed western horizon to see it low above the western horizon. During the month of August, Venus sets at best only about an hour after the Sun; not until late October will it become truly prominent. Saturn is still visible low in the west at the beginning of August, setting a little over an hour after the Sun. Venus and Mercury pass very close (as seen from Earth) to Saturn on the 13th and 15th, respectively, making for a marvelous sight in binoculars or a small telescope. By months end, however, Saturn will have disappeared into the evening twilight, only to reappear in September in the morning sky before sunrise.

Mars can be spotted in the western sky shortly after sunset, to the upper left of Saturn and Venus. Mars is now on the opposite side of the Sun from the Earth, and hence is much fainter than it was back in December 2007 when it was closest to Earth. Mars sets about one and a half hours after the Sun in mid-August. Jupiter is in fine position for viewing this August. It resembles a brilliant cream-colored star as it hovers above the southeastern/southern horizon during the evening hours. Jupiter continues to reside within the constellation Sagittarius, just to the east of the famous teapot asterism. In mid-August, Jupiter reaches its highest point above the southern horizon (i.e., transits the meridian) around 10 pm and sets at about 3 pm.

Earth passes through the debris of Comet Swift-Tuttle on August 11-12, producing the Perseid Meteor Shower. Meteors should become visible in late evening, with the best show occurring after midnight. Look toward the northeast, but meteors can be seen in any part of the 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