December 2008

Skywatcher’s Guide for December 2008

HIGHLIGHTS: The two normally brightest planets, Venus and Jupiter, are spectacularly grouped with the crescent Moon in the evening twilight of December 1. They continue to be paired early this month and are easily seen with the unaided eye in bright evening twilight. The two will gradually move farther apart in the sky as the month progresses, with Jupiter sinking lower, to be paired with Mercury the last few days of the year.

PLANETS

The evening sky on Dec. 1/2 at 6:30 p.m. MST. This sky chart is most useful for the southern United States and northern Mexico. The evening sky on Dec. 29 and 31 at 6:30 p.m. MST. This sky chart is most useful for the southern United States and northern Mexico. The sky on Dec. 18 and 19 at 12 midnight MST. This sky chart is most useful for the entire United States, southern Canada and northern Mexico.

The brilliant planet Venus continues to move higher above the southwestern horizon and into the evening twilight this month. White Venus is the brightest star like object normally ever seen in the sky. Venus starts December about 22 degrees above the west-southwestern horizon about 45 minutes after sunset, and creeps higher each evening, reaching 30 degrees above the southwestern horizon at that time by December 30. On the evening of December 1, the 4-day-old crescent Moon is above tightly grouped Venus and Jupiter, creating a spectacular grouping of the three brightest solar system objects that can be normally seen in the western evening twilight sky.

Bright Jupiter is paired with brilliant Venus during the first week of December in twilight and for an hour after sunset. The gas giant continues to sink lower below brilliant Venus as the month progresses. During the first half of December Jupiter is visible 30 minutes to one hour after sunset as a very bright white star-like object, above the southwestern horizon. Jupiter is still bright (around magnitude -2.0) and large in a telescope (34 arc seconds), early in the month but continues to fade somewhat, especially as it nears the southwestern horizon. Jupiter is paired with dimmer Mercury at the end of December: Look for the waxing crescent Moon above the two on December 29. Mercury and Jupiter are closest in our sky and just over one degree apart on December 31, when the Moon is beautifully grouped with Venus.

Although Jupiter is really too low for viewing cloud details in a telescope, sharpest views of the gas giant should be just after sunset in evening twilight, when at or near its highest in the twilight sky early this month. As with any planet viewing is dependent on atmospheric stability and conditions, planet altitude in our sky, 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. Jupiter sets in the west-southwest early around 8:30p.m. on December 1, and around 7:30 p.m. on December 15.

Saturn rises earlier and creeps higher above the eastern horizon in the pre-dawn hours this December. In early December Saturn rises around 1:00 a.m. but by late December rises just after 11 p.m. Look for Saturn in early December in the morning twilight high overhead as a 1st magnitude star-like object, 90 minutes to one hour before sunrise. Saturn is found in the constellation Leo the Lion, far below its bright star Regulus. The 24-day-old waning crescent Moon is found below and nearest Saturn in our sky on Thursday morning, December 18.

Faint Mars is now lost in the glare of the Sun until it reappears as a dim object in the February morning sky.

Visitors to Flandrau’s 16-inch telescope should note that due to the low position of planets in the evening sky only Venus is briefly visible at the end of this month in the telescope after it opens at 7 p.m. The telescope normally closes at 10 p.m.

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 right now, note that it may appear to twinkle somewhat; however, this twinkling is of a slower nature than the bright stars

GEMINID METEOR SHOWER WASHED OUT BY MOONLIGHT

This sky chart shows the eastern sky at 8:45 p.m. on Dec. 13 (MST) from the Desert Southwest.

On December 13-14 (Saturday night into Sunday morning), the bright Geminid meteor shower is at its best, from late evening until first light of dawn. The waning gibbous moon this year unfortunately is nearly full, and, located in the middle of Gemini, the Twins, will wash out all but the brightest of shooting of stars. Although the Geminids are considered one of the best meteor showers of the year, the moon makes this a very unfavorable year to see this shower, as it’s in about the worst position and phase possible for this year’s shower. Stargazers who want to try for some meteors through the moonlight can start viewing by 8 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. This year expect to see upwards of 10 meteors per hour in a clear, dark sky away from city lights. Glare from artificial light sources will certainly reduce the amount of meteors seen, so even with the moonlight dark sky sites such as Saguaro National Park East (east ends of Speedway and Broadway Boulevards) are recommended.

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. (Mars is not shown.) 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 Sunday, 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 5:04 a.m. MST or Tucson time on Sunday morning 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 December first quarter Moon will occur on Friday evening, December 5. The December Full Cold Moon rises on the evening of Friday, December 12 and sets on the morning of Saturday, December 13. The December last quarter Moon occurs on Friday morning December 19. The December 2008 new moon will occur on Saturday, December 27.

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.

Graphics done using Starry Night Pro and Adobe Photoshop. To purchase Starry Night Enthusiast go to http://StarryNight.com