October 2006
Mercury begins the month shining, with an orange hue, at magnitude –0.1, in the constellation Boötes, the herdsman. Look for the planet low in the west-southwest about thirty minutes after sunset during the first half of October. To see it, though, you'll probably need optical aid and a ton of luck. Although it attains its greatest elongation, twenty-five degrees from the Sun, on October 17th, it remains south of the celestial equator, in the constellation Libra, the scales, and so lies low in the sky for observers in the Northern Hemisphere. By the end of the month, Mercury is so low and faint that few viewers north of the equator can see it at all.
Venus is out of sight in October; it reaches superior conjunction, on the far side of the Sun, on the 27th. The planet returns as a bright evening “star” by early to mid-December.
Mars, like Mercury and Venus, is hidden deep in the Sun's glow throughout the month. The Red Planet is in conjunction with the Sun on the 23rd.
Jupiter sets about an hour and three-quarters after the Sun at the start of October, but fifty minutes after sunset by month's end. Unfortunately, the solar system's largest planet is too low at dusk for good telescopic viewing, but binoculars help a lot. My guess is that, realistically, the evening of the 24th is the last time most observers can see it this month. If you do locate Jupiter that evening, try to spot the exceedingly thin crescent Moon about ten degrees to the planet's left, albeit somewhat lower in the sky. You might also spot dim Mercury, about four degrees below and to the left of Jupiter. Binoculars can also track Jupiter as it pulls away from the star Zubenelgenubi, in the constellation Libra, early in the month.
Shining at magnitude +0.5, Saturn reigns over the October skies, the only bright planet well placed for viewing. At midmonth it rises soon after 2 a.m. and is a good distance above the eastern horizon at dawn. Saturn creeps 2.5 degrees eastward in the constellation Leo, the lion, and closes the month six degrees west of the bluish, first-magnitude star Regulus, also in Leo. Of all the stars within thirty degrees of Saturn, only similarly hued Procyon, in the constellation Canis Minor, the little dog, shines brighter than the Ringed Planet. The edge of the rings continues tilting slowly toward our line of sight; a telescope shows the rings' southern side tilted 13.7 degrees toward us at the start of the month and 12.7 degrees by month's end. On the morning of the 16th Saturn lies below and slightly to the right of a fat crescent Moon.
The Moon is full on the 6th at 11:13 p.m. Because this full Moon is the one closest to the autumnal equinox, it is also known as the Harvest Moon. Late on the night of the 9th and into the early morning hours of the 10th, in its waning gibbous phase, the Moon occults, or passes in front of, the Pleiades star cluster. Because the Moon is so bright at the beginning of the occultation—87 percent of its disk is illuminated—viewing the stars may be difficult. It may be particularly hard to see them disappear, because the bright edge of the Moon passes in front of them first. It should be easier to catch them as they pop out from behind the dark edge. The Moon further wanes to last quarter on the 13th at 8:26 p.m., and to new Moon on the 22nd at 1:14 a.m. Our satellite waxes to first quarter on the 29th at 4:25 p.m. eastern standard time.
Daylight saving time ends on the 29th, the last Sunday of the month. People in most of Canada and the U.S. should set their clocks back one hour. On this date the “clock hour” from 1 until 2 a.m. officially repeats.
Unless otherwise noted, all times are given in eastern daylight time. Joe Rao is a broadcast meteorologist and a lecturer at the Hayden Planetarium.
Copyright © Natural History Magazine, Inc., 2006