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01 Dec 2016

December Astronomy: Venus Dominates the Sky, While the Full Moon Puts a Damper on the Geminid Meteor Shower

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Evening twilight: Venus rules! You won’t fail to notice this brilliant light in the southwest at dusk. Look for Mars to its upper left, and, for the first two or three weeks of December, Mercury to Venus’ lower right, provided you have an unobstructed view. The moon passes through this section of sky Nov. 30-Dec. 5.

The Summer Triangle of Vega, Altair, and Deneb is not far west of overhead in twilight in early December, and drifts westward as this month progresses. Blue-white Vega is next in brightness after Venus among objects visible in December’s evening twilight. Yellow Capella in the northeast is almost as bright. To Capella’s lower right, red-orange in color, is Aldebaran, eye of Taurus, the Bull, ascending in the east-northeast to east. Later in the month, Orion’s brightest stars, reddish Betelgeuse and bluish Rigel, rise almost together not far from due east. In December at dusk, look for Fomalhaut, mouth of the Southern Fish, crossing the southern sky about 25 degrees above the horizon.

Later in the evening, Orion is higher, and now the “Dog stars,” Sirius and Procyon, following the Hunter across the sky, have risen into view. Notice that Orion’s belt points downward to Sirius, the brightest star, and upward toward Aldebaran and the Hyades star cluster, and beyond to the Pleiades, or Seven Sisters, star cluster. Both star clusters are spectacular fields for binoculars!

Morning twilight: Now Orion and company are descending in the western sky, with some stars already out of view. Jupiter is the dominant “morning star” in the southeast to south, with first-magnitude Spica in Virgo not far below. After Sirius departs in the southwest, the brightest actual star remaining is golden-orange Arcturus in the east. Vega, reincarnated in the northeast, and Capella, sinking in the northwest, are almost as bright. Regulus, heart of Leo, the Lion, is high in the southern sky, going west as weeks pass. Before month’s end, watch for Antares and Saturn emerging out of the sun’s glare in the southeast.

Moon and planets: Watch the waxing crescent moon pass three planets Nov. 30-Dec. 5. The moon will appear to the upper right of Mercury on Nov. 30; above Mercury and to the lower right of Venus on Dec. 1; near Venus on Dec. 2 and 3; and near Mars on Dec. 4 and 5. Mercury stays 24 degrees to the lower right of Venus Dec. 2-12, then falls away and fades. Venus-Mars are 23 degrees apart on Dec. 2, narrowing to 12 degrees on Dec. 31.

See Venus in daytime: On Tuesday, Dec. 6, Venus follows the sun’s path. Place the sun just above an object such as a treetop or building around midday or in the afternoon. Return to the same observing location three hours and 12 minutes later, and Venus will appear in the same spot! On that date, telescopes show Venus two-thirds full. Watch for big changes in coming months, as Venus draws closer to Earth and becomes backlighted by the sun.

Aldebaran, eye of Taurus, is occulted by the moon on evening of Monday, Dec. 12. Since the moon is almost full, a telescope is needed to observe the star’s disappearance and reappearance. From the Coachella Valley, the leading dark edge of the moon covers the star shortly after 7:02 p.m., and the star reappears at the moon’s bright edge at 8:09 p.m.

The full moon on Tuesday, Dec. 13, rises within a quarter-hour after sunset. The peak of the Geminid meteor shower later that night will be greatly spoiled by moonlight; only the brighter meteors will be seen. Meteors might appear anywhere in the sky. To check if a meteor is a member of the Geminid shower, extend its track backward beyond the point where you saw the meteor light up. The track should extend back toward the radiant of the shower, near the star Castor in Gemini. Castor is very low in the northeast two hours after sunset, and nearly overhead shortly before 2 a.m.

After passing full, the waning gibbous moon, in the morning sky, passes the Twin stars Pollux and Castor in Gemini on Dec. 16; and Regulus, heart of Leo, on Dec. 18.

Winter begins on Dec. 21 at 2:44 a.m. On the next morning, Dec. 22, the moon appears as a thick crescent near Jupiter and Spica, and then several days later on Dec. 26 and 27 as a much thinner crescent near Antares and Saturn.

On Tuesday, Dec. 27, as morning twilight brightens, bright Jupiter is in the south-southeast, approaching its high point in the south. Look low in the southeast to east-southeast for the last easy old crescent moon, with Saturn 4 degrees below. In late December, Jupiter and Saturn are 60 degrees apart.

On Wednesday, Dec. 28, the old moon is hard to see, but it’s worth trying for rare opposing crescent moons on consecutive days: Dec. 28 at dawn, and Dec. 29 at dusk. On Dec. 28, using binoculars 20 to 30 minutes before sunrise, try for the crescent moon rising 9-10 degrees to the lower left of Saturn. The new moon occurs later that day, at 10:53 p.m. At early dusk on Thursday, Dec. 29, about 20 minutes after sunset, note Venus well up in the southwest. Using binoculars, try for the young crescent moon within 39 degrees to the lower right of Venus. To see the old moon on Dec. 28 and the young moon on Dec. 29, you’ll need very clear skies, unobstructed views, and binoculars or a telescope. Good luck!

On New Year’s Eve, you can conveniently find the most distant planet of our solar system. Get your telescope out at nightfall (about 90 minutes after sunset), and point it at Mars. Neptune, very faint at eighth magnitude, will appear very closely east of Mars, following the red planet through the telescopic field. As the evening progresses, Mars will appear to close in on the dim, more-distant planet.

Star parties: They provide wonderful opportunities to join with other folks to get great views of astronomical objects through a variety of binoculars and telescopes. The Whitewater Preserve will be hosting a star party on Saturday, Dec. 10, weather permitting, from dusk until 9 p.m. Reservations are requested; please call 760-325-7222.

The Astronomical Society of the Desert will host the next of our series of monthly star parties on Saturday, Dec. 17, from 5 to 8 p.m. They are held at the Visitor Center of the Santa Rosa and San Jacinto Mountains National Monument, on Highway 74, within 4 miles south of Highway 111 in Palm Desert. Check www.astrorx.org for listings of our high altitude star parties at Sawmill Trailhead starting at dusk. The next one (at 4,000 feet—wear warm clothes!) will be held on Saturday, Dec. 3. Also, check the link to our “Impromptu Star Parties,” which could be announced on short notice at any time.

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 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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