The sky in October

Natural History, Oct, 2005 by Joe Rao

Mercury, shining at magnitude zero, can be seen shortly after sunset all month, albeit with some difficulty. To find the planet, use binoculars to locate Venus in the southwestern sky. Mercury is twenty-nine degrees to the lower far right of Venus on October 12. By month's end the two planets are four degrees closer to each other. The best chance to spot Mercury also comes at month's end, when it lies below and to the right of the star Antares, in the constellation Scorpius, the scorpion.

Venus glitters low in the southwestern sky at dusk, growing brighter throughout the month. On the evening of the 6th Venus sparkles about four degrees above and to the left of a three-and-a-half-day-old crescent Moon. Through a telescope Venus is a remarkable sight, as it changes in phase from gibbous (two-thirds illuminated) at the start of October to half illuminated by the end of the month.

October belongs to Mars, and after Venus sets, Mars is the brightest "star" in the evening sky. In early October it comes up about half an hour after twilight, and by month's end it rises just twenty minutes after sunset. For best viewing, wait about two hours after Mars rises and take a look once it has climbed at least twenty degrees above the horizon (as seen from forty degrees north latitude). Mars comes closest to the Earth--within 43,137,071 miles--on the 29th at about 11:25 P.M. On the evening of the 18th the nearly full Moon rises well above and to the right of the planet.

Jupiter is in conjunction with the Sun on the 22nd; the planet is lost in the solar glare throughout the month.

Saturn rises in the east-northeast about five hours before sunrise on the 1st and about six hours after sunset at the end of the month. By dawn it has shifted to a point high in the south-southeastern sky. The ringed planet is the brightest "star" in the constellation Cancer, the crab. Saturn starts the month very close to the fourth-magnitude star Delta Cancri and slowly moves away to the east as the month progresses.

The Moon is new on the 3rd at 6:28 A.M. It waxes to first quarter on the 10th at 3:01 P.M. and to full on the 17th at 8:14 A.M. Our satellite wanes to last quarter on the 24th at 9:17 P.M.

A partial eclipse of the Moon takes place on the morning of the 17th. At its maximum, at 7:03 A.M. central daylight time, less than 7 percent of the Moon's diameter will be eclipsed. The umbral phase of the eclipse lasts less than an hour. The Moon sets before the eclipse ends in the central and eastern United States and Canada.

The Sun undergoes an annular, or ring-shaped, eclipse on the 3rd. The entire silhouette of the Moon's disk appears against a brilliant "ring of fire" for four minutes and eleven seconds, beginning at 8:56 A.M. Greenwich mean time. The track of the eclipse makes landfall on the Atlantic coast of Europe, near the border shared by Portugal and Spain. The track then crosses the Mediterranean and sweeps south and east across Africa.

Follow safety tips from the local media when viewing eclipses. Never look at the Sun's disc unless you are using a proper filtering device, such as #13 welder's glass or aluminized Mylar plastic.

Daylight saving time ends on the 30th; people in Canada and the U.S. should set their clocks back one hour.

Unless otherwise noted, all times are eastern daylight time.

CHARLES LIU is a professor of astrophysics at the City University of New York and an associate with the American Museum of Natural History.