December 2009
Skywatchers’ Guide for December 2009
THE GEMINID METEOR SHOWER PEAKS ON DECEMBER 13!
 This sky chart shows the eastern sky at 8:45 p.m. on Dec. 13 (MST) from the Desert Southwest. |
On December 13-14 (Sunday night into Monday morning), the bright Geminid meteor shower is at its best, from late evening until first light of dawn. The moon is a waning crescent, and rises around 5 a.m. on the 13th, making it a great year for viewing this major meteor shower! The Geminids are considered one of the best meteor showers of the year, and should be much more impressive than this year’s Leonid shower. Stargazers can start viewing by 8 p.m. or 9 p.m. to see this major meteor shower, which lasts all night long. Conversely, early rises can simply get up at 4 or 5 a.m. to catch some shooting stars before sunrise. If you see a bright Geminid meteor, you should be able to trace its path backward to a point in the sky near Castor and Pollux, the Gemini twins. To see the shower simply look high in the eastern and northern sky and overhead after 8 p.m. Expect to see upwards of 50 meteors per hour in a clear, dark sky away from city lights, into the late night hours. If it is cloudy on the night of December 13-14, meteors can also be seen in numbers on Saturday night and on Monday night.
Dark viewing locations are highly recommended: glare from any artificial light sources will certainly reduce the amount of meteors seen. Dark sky locations in Tucson favored for viewing this shower will be east of Tucson, such as Saguaro National Park East, at the east end of Speedway and Broadway Boulevards (dress warmly!).
PLANETS
 The evening sky on December 18 around one hour after sunset facing southwest. This sky chart is most useful for the southern United States and northern Mexico.  The evening sky on December 20 around one hour after sunset facing southwest. This sky chart is most useful for the southern United States and northern Mexico.  The eastern late night sky with Mars and the Moon on December 7 at around 12:00 a.m. (MST). This sky chart is most useful for the United States, southern Canada and northern Mexico.  The morning sky with Mars, Saturn and the Moon on December 10 at around one hour before sunrise, looking overhead. This sky chart is most useful for the United States, southern Canada and northern Mexico. |
Bright Jupiter continues to dominate the southern sky on evenings this December but is setting earlier into the southwestern horizon. This month, as during November, the best time to view it will be during the first half of the month, when it’s up longer in our sky. Jupiter sets by 10:30 p.m. in early December, by 9:30 p.m. on December 22, and by 9:00 p.m. on December 31. Gas giant Jupiter appears one hour after sunset as a very bright, almost brilliant white star-like object, high above the south-southwestern horizon in early December evenings, but moving earlier toward the southwestern horizon by the last half of December. On December 1 Jupiter is still bright (at magnitude -2.2) and large in a telescope (around 38 arc seconds wide). By December 30 it’s 35 arc seconds wide and has faded slightly. Early to mid-December continues to be a very good time to view the giant planet in the evening twilight and 1-2 hours after sunset. Look for bright, whitish Jupiter in Capricornus, the Sea Goat, far east (or roughly far ‘left’) of the Teapot of Sagittarius: It’s the brightest star like object well up in the evening sky in December. Jupiter is highest and due south in bright evening twilight in early and middle December (at around 37 degrees in altitude for much of the Desert Southwest). Also, look for the waxing crescent Moon to slide below (and south) of Jupiter in the southern sky on Sunday evening, December 20.
When looking at Jupiter in a telescope to view its cloud belts and festoons, the sharpest views should be just after sunset in evening twilight, when at or near its highest in the twilight sky this month. As with any planet viewing is dependent on atmospheric stability and conditions, and of course, the quality and size of the telescope used. However to view its moons, a good pair of binoculars is all that’s needed.
The planet Mars is noticeably brightening in our late night and morning sky, starts December as a false bright, rusty-orange star ‘within’ the constellation of Cancer, the Crab, but moves into Leo, the Lion this month. Mars is moving closer to Earth and more than doubles in brightness from -0.1 magnitude to -0.7 magnitude while widening from 10 to 12.7 arc seconds in apparent diameter (suitable for imaging and viewing in amateur telescopes). Also look for the waning gibbous Moon to rise nearest Mars in our sky this month at around 10:30 p.m. on Monday, December 7.
Ringed Saturn rises earlier above the eastern horizon in the predawn hours this December. In early December look for Saturn in the morning sky 1-2 hours before sunrise high above the eastern horizon as a slightly brighter than 1st magnitude star-like object. By early December Saturn is about 50 degrees above the eastern horizon, one hour before sunrise, and by late December climbs overhead before the start of twilight to its highest possible altitude during this apparition (57 degrees in altitude). Saturn is found below the constellation Leo the Lion in Virgo, the Virgin. Also look for the waning crescent Moon to appear closest with Saturn in our sky on Thursday morning, December 10.
The elusive planet Mercury has a fairly favorable apparition and might be glimpsed in the evening sky this December with the naked eye, close to the southwestern horizon, one hour after sunset. Mercury will be around -0.5 magnitude in brightness during the first three weeks of December but is best visible after December 10 through December 25, when it is highest above the horizon. As is usually the case with viewing Mercury, very clear skies are needed to best observe it. On December 17 a razor thin, 1.4 day old waxing crescent Moon is nearest Mercury, an observing challenge in binoculars (look 30-45 minutes after sunset). The Moon will be much easier to view and higher the following evening.
The brilliant planet Venus is nearly lost in the glare of the Sun near the eastern dawn horizon. It might be glimpsed during the first 10 days of December in the naked eye or binoculars, very close to the eastern horizon, 20-30 minutes before sunrise.
Visitors to Flandrau’s 16-inch telescope should note that Jupiter is visible in the telescope during public hours (closed on Thanksgiving and Christmas Days). Other celestial objects will be shown in the telescope, weather permitting. Although Flandrau’s main exhibit hall and planetarium are now closed to the general public due to state budget cuts, school groups can arrange for planetarium and Mineral Museum field trips. The Mineral Museum is normally open Friday and Saturdays to the public from 9:00 a.m. to 5:00 p.m. (and by appointment). The Flandrau Observatory remains open for viewing during public hours from 7-10 p.m., weather permitting, Wednesday through Saturday nights (excluding select holidays). Finally, remember that in spotting planets there is a general rule: ’stars twinkle, planets don’t’. This is because stars are point sources of light; therefore starlight is easily disturbed and shifted by air currents in the Earth’s atmosphere. However when looking at Mercury or Mars this month, note that they appear to twinkle somewhat; however, this twinkling is of a slower nature than that of the bright stars.
DECEMBER STARS
 This chart shows the eastern sky at 9 p.m. on Dec. 15, from Arizona, but is also for use in early December at 10 p.m. and in late December at 8 p.m.  The December evening night sky looking above the western horizon around 11 p.m. in early December, from 10 p.m. in mid-December and around 9 p.m. in late December. |
In late December and early January look in the east for the bright stars of winter to rise around 8 p.m. Orange Betelgeuse, the shoulder of Orion the Hunter, shines left of Orion’s 3 glittering belt stars. The Gemini Twins, the bright stars Castor and the slightly brighter Pollux, twinkle left of Orion. An hour later, by 9 p.m., the bright star Procyon (whose name means “Before the Dog”) is newly risen in the east. From Tucson’s latitude, the Dog, – that is the “Dog Star” Sirius– the brightest star in all the heavens, rises almost at the same time as Procyon, so Procyon’s name isn’t so true this far south. Once it rises, brilliant Sirius will dramatically flicker different colors when low in the sky, making for a wonderful sight to the naked eye and in binoculars; such flickering is due to earth’s atmosphere.
Leaving center stage and moving to the western half of the sky in December is the Great Square of Pegasus. Find the Great Square (before 8 p.m. in early to middle December) quite a ways up from Fomalhaut, the bright star marking the Southern Fish (Pisces Austrinus), which lies low in the southwest. In December the Great Square can also be found all month long (before 10 p.m.) by facing west and looking far above and left (or southwest in this instance) of the bright star Deneb. At 10 p.m. Deneb, the brightest star of Cygnus, the Swan (whose other name is the Northern Cross), will lie above the northwestern horizon. The eastern corner star of the “Great Square” of Pegasus, Alpheratz, is actually also the head of Andromeda, the Chained Lady or Princess. In Andromeda, is the “Great Andromeda Galaxy”, M31, which can be viewed as a fuzzy spot in binoculars. High overhead (and far from M31) is the Seven Sisters (or Pleiades) star cluster, a wonderful sight in binoculars.
Winter Solstice on Monday, December 21
Days become shorter in the fall due to the lower altitude of the sun in the Northern Hemisphere sky. The shortest day for the Northern Hemisphere is always on the Winter’s Solstice, which this year officially begins at 10:47 a.m. MST or Tucson time on Monday December 21. From this time forward the sun now gains altitude in our Northern Hemisphere sky as winter now begins for the Northern Hemisphere (and summer for the Southern Hemisphere). Also, although the 21st marks the shortest day, the earliest sunset occurs on December 7th (for much of the Northern Hemisphere). The discrepancy between shortest day and earliest sunset is due to the use of average or ‘mean time’ across times zones.
MOON PHASES
The ‘Moon Before Yule’ and the December ‘Full Cold Moon’ will rise on the evening of Tuesday, December 1 and set on the morning of Wednesday, December 2, while a second ‘Blue Moon’ in December will rise on the evening of Thursday, December 31 and set on the morning of January 1, 2010. The December last quarter Moon occurs on Tuesday morning December 8. The December new moon occurs on Wednesday, December 16. The December 2009 first quarter Moon will occur on Thursday evening, December 24.
Note: Additional information can be accessed by phone at Flandrau Science Center’s Astronomy Newsline at (520) 621-4310 or as a menu option at 621-S-T-A-R.
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