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The sky in October

Natural History, Oct, 2004 by Joe Rao

Mercury reaches superior conjunction--on the opposite side of the Sun from Earth's vantage point--on the 5th, and thereafter moves into the evening sky. But the planet remains hidden in the glow of sunset throughout the rest of October.

Venus, at magnitude -4.1, dominates the eastern sky for more than three hours before sunrise. It is the brightest morning "star" this month, and remains so throughout autumn. Although Venus appears less luminous and slightly lower in the sky than it did in September, the planet still dazzles. Seen through a telescope on successive nights, however, the planet is shrinking. Before dawn on the 3rd, Venus appears only 0.3 degree (about half the apparent diameter of the full Moon) from the star Regulus, as seen the East Coast of the United States, and 0.2 degree as seen from the West.

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Dim, red Mars, shining at magnitude 1.7, emerges from the morning Sun's glare toward the end of October. On the 31st the planet rises in the east-southeast less than an hour and a half before sunrise. During the next twelve months, as Mars slowly approaches opposition, it will rise progressively earlier and become nearly forty times brighter than it is now.

Jupiter leaps out of the glow of sunrise this month. At the beginning of October the giant planet shines low, in the murk above the horizon, as day brightens. But by month's end it beams brightly in the east at dawn, drawing to within five degrees of Venus by month's end. Jupiter is now in the constellation Virgo, the virgin; the planet shines from that constellation for the next year. Because Jupiter takes twelve years to orbit the Sun, it advances though the zodiac by one constellation each year. A slender crescent Moon, just thirty-six hours from new, appears to hover above Jupiter on the morning of the 12th.

Saturn rises in the east-northeast about six hours after sunset on the 1st. By the end of the month the ringed planet rises two hours earlier than it did at the beginning of the month, which, with shortening days and the return to standard time, works out to five hours after sunset. At any rate, Saturn has climbed high in the south-southeastern sky by dawn all month. At magnitude 0.2, Saturn is the brightest "star" in the constellation Gemini, the twins. In the early morning hours of the 7th, sky watchers can see Saturn and a fat crescent Moon hovering near the twin stars Castor and Pollux.

The Moon wanes to last quarter on the 6th at 6:12 A.M. and becomes new on the 13th at 10:48 P.M. It waxes to first quarter on the 20th at 5:59 P.M. and to full on the 27th at 11:07 P.M. That full Moon, the first after the harvest Moon, is sometimes called the hunter's Moon.

On the night of October 27-28 the Moon is totally eclipsed over North America, less than a year after the last such event over the continent. Almost everyone in the Americas and Western Europe has a beautiful view of the eclipse. Over most of the United States and Canada the eclipse begins well after dark, and the Moon is well up in the evening sky; only along the far West Coast does it begin in twilight, just minutes after the Sun has set and the Moon has risen. But by late twilight even westerners will have a fine view of the totally eclipsed Moon, probably glowing dimly like a reddish ember low in the eastern sky. Across much of Alaska the eclipse is already underway when the Moon comes up; over southwestern Alaska, the Moon rises totally eclipsed, appearing like a weird, mottled, dim ball among the twilight stars. Over Hawai'i, moonrise conies just after the end of totality; the Moon gradually emerges from Earth's shadow as the satellite rises.

Totality lasts eighty-two minutes, which is somewhat longer than average, because the Moon tracks through the northern portion of the Earth's shadow. Unless airborne volcanic aerosols or other atmospheric effects influence its appearance, the Moon's disk should appear relatively bright, particularly during the beginning and end of totality. The upper part of the Moon is likely to appear brightest and to glow with a ruddy or coppery hue, whereas the lower half of the Moon should look more gray or chocolate.

The Moon enters the Earth's shadow at 9:14 P.M. on the 27th. Totality begins at 10:23 P.M.; mid-eclipse comes at 11:04 P.M. and totality ends at 11:45 P.M. The Moon exits the shadow at 12:54 A.M. on the 28th.

The Sun is partially eclipsed by the Moon late on the afternoon of the 13th. Sky watchers living in the western half of Alaska can see the eclipse reaching a spectacular peak just as the Sun is setting below the west-southwestern horizon. Look for an eerie counterfeit twilight to fall over the landscape just prior to sunset.

Never look at even the smallest sliver of the Sun's disc unless you are using a proper filtering device, such as #13 welder's glass or aluminized Mylar plastic, to protect your eyes. You'll get all the safety tips from the local media--be sure to observe them!

Daylight saving time ends on the 31st, the last Sunday in October. Clocks in Canada and most of the U.S. (with the exceptions of Arizona, Hawai'i, and Indiana) are set back one hour, and the clock hour from 1:00 A.M. until 1:59 A.M. is repeated. The mnemonic is "spring ahead; fall back."

The sky in October

Natural History, Oct, 2004 by Joe Rao

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