What’s Up in the Sky – December, 2010
By Peter Burkey
This is a “good news/bad news” month. The good news is there will be a total eclipse of the Moon visible from North America on the night of December 20-21, the first one we have been able to see since February, 2008. The bad news is that totality does not start until 2:41 a.m.
A lunar eclipse occurs when the Moon passes through the shadow of the Earth. Unlike a solar eclipse, which is visible only along a narrow path on Earth’s surface, a lunar eclipse is visible to anyone who can see the Moon. Since lunar eclipses can be seen (assuming the sky is clear) from the entire night side of the Earth, they are much more frequently observed from any particular location than are solar eclipses. The next total eclipse of the sun visible from the US will not be until 2017.
A lunar eclipse can only take place when the Moon is full. About 20 minutes before the Moon reaches the dark central shadow of the Earth, it dims somewhat as the Earth partly blocks the sunlight. As the Moon begins to move into the shadow, the curved shape of the Earth’s shadow can be seen. Aristotle listed the round shape of the Earth’s shadow as one of the earliest proofs of the fact that the Earth is spherical.
Even during totality the Moon is still visible, appearing a dull, reddish color. This is due to sunlight which has passed through the Earth’s atmosphere and has been bent by the air into the Earth’s shadow, sort of like all the sunsets on Earth being cast on the Moon.
Besides this spectacular event, which occurs in the wee hours of the morning, an easier sight can be seen the next few days. Look SE tomorrow morning around 7:00 a.m. for bright Venus. To the upper right of the planet is the crescent Moon and above that can be seen Saturn. For those of you with an early morning commute, these two planets will put on a pretty good show up in the sky.
This month in history:
Dec. 3: Pioneer 10 spacecraft makes closest approach to Jupiter – 1973
Dec. 7: Apollo 17, final Moon landing mission, launched – 1972
Dec. 11: First auction of Soviet space hardware and artifacts – 1993
Dec. 14: Gene Cernan, Apollo 17 astronaut, is last human to walk on Moon – 1972
Dec 17: Orville Wright makes first powered flight – – 1857
Dec. 24: Apollo 8 makes 10 orbits of the Moon – 1968
Dec. 27: Meteorite ALH 84001 discovered – 1984
Dec. 31: First flyby of Saturn’s moon, Iapetus, made by Cassini spacecraft – 2004
Here are this month’s viewing highlights:
Planets this month: Jupiter is high in south at nightfall, great for telescopic viewing. Saturn and Venus are “morning stars” visible in the SE before dawn.
Dec. 2: Waning Crescent Moon lower right of Venus in predawn sky.
Dec. 5: New Moon
Dec. 13: First Quarter Moon
Dec. 13-14: Geminid meteors peak
Dec. 21: Full Moon – lunar eclipse 2:40 – 4:00 a.m.
Dec. 21: Winter solstice – first day of winter – 6:38 p.m. EST
Dec. 27: Last Quarter Moon