August 2006

by Deane Morrison

The warm, lazy nights of August are perfect for exploring the richness of the night sky. This month the planets all hug the horizon, as if standing back to let the perennial beauty of the stars shine through.

Jupiter, a beacon in the southwest at sunset, sets earlier each night; by month's end it will be gone by 11 p.m. The planet is unmistakable, shining west of the baleful red Antares, the heart of Scorpius, in the south. Mars, the other evening planet, is close to the western horizon and sets very soon after sunset, before twilight has faded.

Venus still rules the morning sky but drops ever farther toward the rising sun. Still, Venus is worth a look, especially the mornings of the 18th and 19th, when it will be near the Beehive star cluster. Binoculars will help in finding the Beehive when it's this low in the sky. You may spot Mercury just below Venus the second week of the month, or Saturn as it pops above the eastern horizon a little later on. By the end of August, Saturn will be higher than Venus, and Mercury will have disappeared.

The full moon of August, called the green corn moon or the grain moon, arrives at 5:54 a.m. CDT on the 9th, only a few minutes before setting. If you're up early you can see it glowing soft and round in the west against the pale morning twilight.

A few nights later, that nice pretty moon causes mischief by spoiling the Perseid meteor shower. The shower peaks in mid-day on the 12th, but the nights of the 11th and 12th will both share the sky with a bright waning moon. The moon earns some measure of redemption, however, on the morning of the 22nd, when its thin, waning crescent rises between Venus and Saturn in the predawn sky.

The stars offer many delights, especially along the Milky Way stretching from northeast to southwest during the evening. Start with Sagittarius and Scorpius in the south and move up along the Milky Way to the Summer Triangle of bright stars. Southernmost is Altair, in Aquila, the eagle; next comes brilliant Vega, in Lyra, the lyre, a little bit west of the Milky Way; then Deneb, in Cygnus, the swan. Deneb lies in the direction our solar system is moving as it makes its way through the disk of the Milky Way. Moving past Deneb, the W- or M-shaped chair of Cassiopeia points the way to Perseus, near the northern horizon.

In one of its most predictable performances, the sun is slowly sinking in the northern sky this month. But in other ways the sun is quite unpredictable, such as when it occasionally hurls pieces of its corona off into space. In August this year, NASA is set to launch twin spacecraft, called STEREO, which will orbit the sun ahead of and behind the Earth, giving us our first stereoscopic view of these solar outbursts. Several University of Minnesota physicists have designed and built instruments that will be aboard both spacecraft, helping researchers better understand and predict the doings of our parent star.

The feast of Lammas, celebrated the 1st of August, began as a Celtic holiday called Lughnasaid (LOON-eh-sed). It was one of the Celtic world's four cross-quarter days, falling midway between a solstice and an equinox. The other cross-quarter days are Imbolc (Groundhog Day), Beltane (May Day) and Samhain (Halloween). Lughnasaid was a harvest festival at which bread baked from the new crop of grain was served. The Christian Church adopted the holiday as the Loaf Mass, which was eventually corrupted to Lammas.