The sky in September

Natural History, Sept, 2002 by Joe Rao

Mercury spends most of September too near the Sun to be seen from Earth. On the 27th it reaches inferior conjunction.

Venus begins September shining low in the west-southwest after sundown, less than 1[degrees] from Spica, in Virgo, and sinks a little deeper into the glow of twilight every day. The planet reaches greatest brilliancy (magnitude -4.5) on September 26. By the 30th, it sets well before the end of twilight. Most of Venus's sunlit hemisphere faces away from Earth, leaving us with a lovely waning crescent; through a telescope, observers can see it growing rapidly thinner and longer as the month progresses. For laypersons, a crescent Venus is a favorite telescopic sight, although a few people will insist that the planet is the Moon, even when our satellite is in a different phase or not visible at all. The late George Lovi, a well-known Hayden Planetarium astronomy lecturer and author, once had just such an experience while conducting a public event at the Brooklyn College Observatory. The telescope was pointed right at Venus, yet one student insisted he was seeing the Moon. When Lovi commented that the Moon wasn't even in the sky, the student replied, "So what? Doesn't a telescope show you things you can't see without it?"

Mars is still too near the Sun to be readily seen for much of this month. Ocher-hued and resembling a second-magnitude star, it appears above the east-northeastern horizon about one and a half hours before sunup in late September.

Jupiter rises at about 3:45 A.M. local daylight time at the start of the month but comes up about ninety minutes earlier by the end. The largest planet, it now resides in Cancer; looking for Jupiter with your binoculars early in September reveals the pretty Beehive star cluster just above it. The planet passes about 1[degrees] south of this spattering of faint stars (also known as Praesepe or M44) on the 4th. The same morning, a crescent Moon hovers nearby.

Saturn slowly becomes more visible during the late evening. Rising at about 12:45 A.M. local daylight time on September 1, it is up before midnight by the 13th and just before 11:00 P.M. by month's end. At the start of September it passes out of Taurus and into the club of Orion. On the 21st, Saturn reaches western quadrature--90[degrees] west of the Sun. The planet's shadow, now highly visible, is cast on the wide-open rings, and the effect suggests an image in 3-D. Saturn is the yellowish zero-magnitude "star" below and to the right of the last-quarter Moon on the night of September 28-29.

The Moon is new on September 6 at 11:10 P.M., waxing to first quarter on September 13 at 2:08 P.M. Full Moon comes on the 21st at 9:59 A.M. Since this is the full Moon closest to the autumnal equinox, it is designated the harvest Moon. It wanes to last quarter on September 29 at 1:03 P.M.

The autumnal equinox occurs at 12:55 A.M. on September 23, when the Sun crosses the equator into the Southern Hemisphere.

Unless otherwise noted, all times are given in Eastern Daylight Time.