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The sky in September
Natural History, Sept, 2005 by Joe Rao
Mercury, shining at magnitude -1.2, can be glimpsed with the naked eye during the first week of September, even though it is barely above the eastern horizon at middawn. On the morning of the 4th the first-magnitude star Regulus can be seen just over one degree (two full-Moon diameters) to the lower right of Mercury. The planet reaches superior conjunction on the 17th, making it invisible in the solar glare as it passes behind the Sun.
Venus and Jupiter will make for an eye-catching pair low in the west-southwestern sky shortly after sunset as September begins. The two appear less than one and a half degrees apart on the 1st, and then gradually separate throughout the month. Venus moves off to the east, while Jupiter slowly descends ever deeper into the sunset glow. Venus was languishing low in the dusk all summer, but now it manages to stay above the west-southwestern horizon during midtwilight.
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Actually, Venus still sets an hour and a half after sundown, as it has all summer, but because twilight shortens as summer wanes, Venus shines in a dark, purple sky before disappearing.
Dazzling Mars has become the "star" of late night as it approaches opposition. This month the Red Planet rises earlier each week; at the beginning of the month it rises around 10:20 P.M., but it's up by about 8:40 P.M. on the 30th. During this period its distance from us decreases from 61 million to 49 million miles, so the planet doubles in apparent brightness, from magnitude -1.0 to -1.7. The best time to view Mars is about 4 A.M., when it is high in the south.
Jupiter should be visible to the naked eye on most clear evenings, at least during the first part of the month. Look for it low in the west-southwestern sky half an hour after sunset. It finally disappears in late September.
Saturn is about one degree from the pretty Beehive Star Cluster, in the constellation Cancer, the crab, during most of the month. The planet shines at magnitude 0.3. On the 15th it rises at about 2:45 A.M.; as the month progresses, it continues to climb in the morning sky. By month's end it is nearly forty degrees above the eastern horizon at the beginning of morning twilight.
The Moon is new on the 3rd at 2:45 P.M. It waxes to first quarter on the 11th at 7:37 A.M. and to full on the 17th at 10:01 P.M. The full Moon that occurs closest to the autumnal equinox is called the harvest Moon, because it provides extra hours of light during the height of the autumn harvest. The Moon wanes to last quarter on the 25th at 2:41 A.M.
The Equinox takes place on the 22nd at 6:23 P.M. The Sun crosses the projection of Earth's equator on the sky and passes into the Southern Hemisphere. Autumn begins in the Northern Hemisphere, spring in the Southern Hemisphere.
Unless otherwise noted, all times are eastern daylight time.
COPYRIGHT 2005 Natural History Magazine, Inc.
COPYRIGHT 2008 Gale, Cengage Learning
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