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Sat12202014

Last updateWed, 27 Aug 2014 10am

Astronomy

Near the start of December every year, the first-magnitude star Aldebaran, eye of Taurus the Bull, and “follower” of the Pleiades, or Seven Sisters, is visible all night as Earth makes its annual passage between Aldebaran and the sun. Look for Aldebaran low in the east-northeast at dusk, high in the south in the middle of the night, and low in the west-northwest at dawn.

On New Year’s Eve, the brightest star, Sirius the Dog Star, reaches its high point in the south in the middle of the night. You can observe Sirius for much of that night, but not at dusk or dawn, because the star’s path from rising to setting is too far south and too short to keep it above the horizon through the long winter night.

Some 21 to 22 minutes earlier, and 36 degrees lower than Sirius at its highest, observers in Southern California can look for Canopus, the second-brightest star visible in the nighttime skies. However, from the Coachella Valley, the star appears 3 to 4 degrees up at its highest. (I’ve spotted Canopus from Palm Springs—as it passed through a gap in the Santa Rosa Mountains.)

The four brightest “stars” at dusk: Venus (after it emerges around midmonth) is at magnitude 3.9; Mercury (near month’s end) -0.8; Vega 0.0; and Capella +0.1.

Watch for the slow emergence of Venus from beyond the sun, followed by Mercury, closing to 3 degrees to the lower right of Venus at month’s end, in the southwest to west-southwest. Binoculars can help you spot Mercury very low in the bright twilight by closing days of December. On Jan. 10, Mercury will approach to just 0.6 degrees to the lower right of Venus! Mars (+1.0 to 1.1) is in the south-southwest to southwest throughout December, to the upper left of Venus.

As for stars: Thee Summer Triangle of Vega, Altair and Deneb is high in the west, still well up at dusk as winter arrives. Fomalhaut, mouth of the Southern Fish, crosses south. Capella is in the northeast, with Aldebaran in the east-northeast, both moving to the upper right as the month progresses. Appearing above the eastern horizon late in the month are Orion’s Betelgeuse and Rigel, and Gemini’s Pollux (with fainter Castor above it, not shown on the map).

The full moon appears closely to the upper right of Aldebaran at dusk on Dec. 5 (passing it overnight), and widely to the lower left of that star on the next evening. On Dec. 22, about 30 minutes after sunset, Venus appears about 6 degrees to the south (lower left) of the young crescent moon. On the next evening, look for Venus about 11 degrees to the moon’s lower right. On Dec. 24, look for Mars 6 to 7 degrees south (lower left) of the moon. On Dec. 5, Mars appears about 11 degrees to the moon’s lower right.

The five brightest “stars” at dawn: Jupiter (magnitude -2.3 to -2.4); Sirius (-1.4); Arcturus (mag. -0.1); Vega (0.0); and Capella (+0.1).

Jupiter is high in the southwestern sky; Saturn (+0.5) is ascending in the east-southeast to southeast.

All of the stars of the huge Winter Hexagon, except Rigel, are visible in the western morning sky at the start of December. As the month progresses, two more of its stars, Aldebaran and Sirius, drop out, as well as Betelgeuse within the Hexagon. The trailing side of the Hexagon, forming the arch of Procyon, Pollux (and Castor, not shown) and Capella, remains in view throughout December. Jupiter and Regulus are close in tow, following the descending arch into the western sky. In the eastern sky, Arcturus dominates, with Vega and Deneb far to its lower left, and Spica to its lower right. Find Saturn to Spica’s lower left and, late in month, Antares below and a little left of Saturn.

The full moon appears closely to the upper left of Aldebaran low in the west-northwest at dawn on Dec. 6. A waning gibbous moon appears between Procyon and Pollux on Dec. 9; near Jupiter on Dec. 11 and 12; and near Regulus on Dec. 12. A waning crescent moon appears near Spica on Dec. 16 and 17; closely to the upper right of Saturn on Dec. 19; and to the lower left of Saturn and upper left of Antares on Dec. 20.

Robert C. Victor was a staff astronomer at Abrams Planetarium at Michigan State University. He is now retired and enjoys providing skywatching opportunities for school children in and around Palm Springs. Robert D. Miller, who provided the twilight charts, did graduate work in planetarium science and later astronomy and computer science at Michigan State University and remains active in research and public outreach in astronomy.

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