Night Sky Guide for December 2009

Meteor Showers, Mercury and Neptune, and a New Year's Eve Full Moon

Nov 15, 2009

The last month of 2009 ends with a bang as two meteor showers peak, two difficult planets temporarily become relatively easy targets, and winter officially begins.

As winter arrives in the Northern Hemisphere it's time to bundle up and enjoy the dark, starry scene.

Spotting Mercury and Neptune in December

The planets closest and furthest from the sun can be a bit of a challenge to spot, but one weekend this month provides a decent shot at bagging them.

On the weekend of December 18, 19, and 20, Mercury is visible with the unaided eye in twilight and Neptune is positioned close to Jupiter for those with telescopes.

On December 18, look southwest after sunset to spot the fleet-footed Mercury. It shines low on the horizon in the sun's fading glow. The crescent moon will be to the upper left of Mercury. Keep looking for Mercury the next two nights, although the moon will separate from Mercury as it heads toward Jupiter.

On December 20, the moon is close to bright Jupiter in the southwest. Use a telescope to spot Jupiter and its moons. Wait until it is dark enough to see the dimmer stars but not before the planet is too low as it sets below the horizon. On December 20, a magnitude-7.68 star in Capricornus is found very close to one side of Jupiter and its plane of moons. On the opposite side of Jupiter from this star and about four times farther away, shining at a similar brightness as that star (magnitude 7.94) is Neptune. A telescope should resolve it into a tiny disk, instead of a pointlike source, helping to confirm identification. It may also have a bluish hue.

Meteor Showers in December

Two meteor showers are found on either side of the new moon this month. First comes the stronger shower, the Geminid meteor shower, which peaks on December 13 in the late evening until dawn. The constellation Gemini rises mid-evening in the east-northeast. The Geminid meteors are unusual in that a comet is not their source, but asteroid 3200 Phaethon. Expect up to 80 meteors an hour at peak.

The second meteor shower of December is the Ursids. These meteors appear to radiate from Ursa Minor, otherwise known as the Little Dipper. This much quieter shower peaks overnight of December 21 and 22. Expect about 9 meteors per hour at peak.

Official Start of Winter

The first day of winter occurs for those in the Northern Hemisphere on December 21 at 12:47 p.m. EST. The sun reaches its farthest point south in the sky, bringing summer to the Southern Hemisphere.

The Moon in December 2009

The moon starts off the first day of the month near the Pleiades and Hyades star clusters in Taurus. It is nearly full, reaching the peak of its full phase at 2:30 a.m. EST on December 2. After sunset on both December 1 and December 2, the moon will appear more than 99% full.

After full phase, the moon rises later each night until it joins the sun for new phase on the 16th. On December 17 and 18, the moon again appears in the evening sky after sunset as a thin crescent in the southwest. On the 18th it is found near Mercury, and on the 20th and 21st it lies near Jupiter.

The last week of December, the moon once again joins the Pleiades star cluster, occulting some of the stars as seen from central and eastern North America. New Year's Eve hosts a full moon, which lies near the twins Castor and Pollux on December 31. This second full moon of the month is sometimes called a Blue Moon.

The copyright of the article Night Sky Guide for December 2009 in Stargazing is owned by Kelly Whitt. Permission to republish Night Sky Guide for December 2009 in print or online must be granted by the author in writing.