December Skies

Tiny but bright Mercury puts in an evening appearance this month for about the first three weeks. Shining at magnitude -0.5 it will be best viewed around the 12^th when is should be seen as a bright dot about 6 degrees above the southwestern horizon about a half hour after sunset.

Jupiter still shines brightly in the early evening sky but will set around 8:30 p.m. by the end of the month. The best viewing will be early evening while it is still relatively high in the sky. For a good part of the month a bonus will be that the planet Neptune will be within one degree of Jupiter and only 0.6 of a degree for several days surrounding the 21^st. For those with telescopes, the tiny blue sphere of Neptune will be found slightly above and to the right of Jupiter.

Venus continues to sink in the eastern sky rising about 45 minutes before sunrise at the beginning of the month. Beginning about the middle of the month the planet will be lost to us in the bright glow of dawn just before sunrise.

Now is the time to view Mars in spite of all those bogus emails that flooded the Internet last summer. Mars will continue to rise earlier each evening and by the end of the month will do so only 3 hours after sunset. We can also watch as Mar’s brightness grows to magnitude -0.7 as the Earth begins to catch up to Mars. However, the closest approach of the Earth to Mars (in January) will see Mars appear only half as big as it did in the summer of 2003. So, if another bogus Mars email shows up in your “inbox” you can happily tell the sender that it isn’t true!

Saturn will rise as early as 11:30 p.m. by the end of the month and will be best viewed in the morning just before the first light of dawn when it is fairly high in the sky. The rings continue to open with their tilt reaching 4.9 degrees from the horizontal by the month’s end.

The Moon will be full on the 2nd, last quarter on the 8^th, new on the 16^th and 1^st quarter on the 24^th and full again on the 31^st making this a “Blue Moon Month.”  On the 5^th and 6^th a waning Moon will bracket the red planet Mars as you look east just above the horizon around 10 p.m. On the 20^th and 21^st the crescent moon will bracket Jupiter.

On December 21^st we will experience the shortest day of the year as the winter solstice begins at 10:47 a.m. MST. For folks “down under” it’s “put another shrimp on the barbie mate, summer has officially begun!”

Jon Spargo
New Mexico Tech Astronomy Club
December 2009