Star Trak: December 2016
FOR IMMEDIATE RELEASE
BLOOMINGTON, Ind. -- Three bright planets will adorn the evening sky in December as Mercury, Venus and Mars gather in the southwest, changing their relative positions from night to night. The morning sky will be less busy, with brilliant Jupiter the only planet visible.
On the evening of Dec. 1, Mercury will appear 5 degrees above the horizon 30 minutes after sunset, bright enough to see with the naked eye, though binoculars may help in finding it. It will climb higher each day until Dec. 10, when it will be 7 degrees high a half hour after sunset. After that it will be lower and fainter each day until it disappears from view around Dec. 19. It will pass through conjunction with the sun Dec. 28.
The time between sunset and when Venus sets will increase about 45 minutes in December for viewers around latitude 40 degrees north, and the planet's altitude at sunset will increase from 24 degrees to 34 degrees. This "evening star" will be bright and easy to spot in the southwest as twilight fades.
Mars will come into view just past the meridian each nightfall in December, but it will be too faint to show much detail in a telescope. Venus and Mars will close dramatically during the month, from 23 degrees apart Dec. 1 to 12 degrees apart Dec. 31. Mars will be 100 times dimmer than Venus, but it will still be conspicuous because of its greater altitude and distinctive red-orange color.
Saturn will pass through conjunction with the sun Dec. 10, so it will not be visible for most of the month. It will be 6 degrees above the southeastern horizon about 45 minutes before sunrise Dec. 31. Binoculars will be needed to see it in morning twilight.
Jupiter will dominate the eastern sky when it rises around 2:30 a.m. at the beginning of December and at 1 a.m. by month's end. The best views through a telescope will be when the planet is 30 degrees above the southeastern horizon an hour after morning twilight begins. It will be at the meridian during dawn by the final days of the month, glowing fairly high in the south as it edges closer to the bright white star Spica.
Meteor showers
December usually features two meteor showers, the Geminids and the Ursids. Unfortunately, a bright full moon will interfere with the Geminids this year when the shower peaks on the night of Dec. 13-14. All but the brightest meteors will be drowned out by moonlight. The "shooting stars" will seem to radiate from the constellation Gemini the Twins. Peak rates can reach 120 meteors per hour in good years, but this time moonlight will probably reduce that by 90 percent.
The Ursid shower will peak on the night of Dec. 21-22. The moon will rise around 1 a.m. local time, so the best views should be within an hour of midnight. The shower's radiant is in the bowl of the Little Dipper, and viewers may see up to 10 meteors per hour in a dark sky.
Solstice
The sun will reach the December solstice at 5:44 a.m. EST (10:44 Universal Time) Dec. 21, marking the start of winter in the Northern Hemisphere and summer in the Southern Hemisphere. For the next six months in the Northern Hemisphere, the days will be getting longer.
Moon
The moon will be at first quarter on Dec. 7, full on Dec. 13, at third quarter on Dec. 20 and new on Dec. 29.
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Hal Kibbey
- Office 812-336-1333
- hkibbey@indiana.edu