December: Busy December Skies

December 2012

Busy December Skies

By Calvin L. Chrisman

There will be much going on in the sky during the middle week of December. During the dawn hours of December 9-11 the waning crescent Moon will pass by several bright, first magnitude stars and two bright planets. On the night of December 13-14 the Geminid Meteor Shower will reach its peak undiluted by any moonlight. Several asteroids will be passing Earth, two of which can be seen in binoculars.

If you are an early riser, you may have noticed the beautiful conjunction between Venus and Saturn on the early morning of November 26th. These two planets, now joined by faint Mercury below and to their left, are moving apart in the east. At the first of next week, the waning crescent Moon will be passing by bright Spica, several other bright stars and these three planets. It will be a striking sight.

The Geminid Meteor Shower promises an excellent show this year. The Moon will be absent, allowing for a very dark sky. Bundle up, allow twenty or more minutes for your eyes to fully adjust, lie back and scan the whole sky. Predictions are for up to 120 meteors per hour with peak activity coming before dawn. The tails of any meteors you see will point back to the constellation Gemini which will be following Orion across the sky. Meteors may appear several nights before and after as well.

As you observe the eastern sky in the early evening, you will notice very bright Jupiter, which is now near the constellation Taurus which is just ahead of Orion. In this area of the sky, the brightest and the largest of the asteroids are reaching opposition. This means that they are directly opposite the Sun from our perspective and are at their most observable. Ceres is the largest of the asteroids and was the first to be discovered in 1801. It is about 585 miles in diameter (roughly one fourth of the diameter of the Moon). Also in the same area of the sky is Vesta. It is only half the size of Ceres, but is the brightest of the asteroids. NASA’s Dawn spacecraft just finished a year of orbiting Vesta and is now on its way to a permanent orbit of Ceres starting in 2015. You can observe these asteroids with binoculars. Go to the Sky & Telescope website to find a chart to help you locate them.

Another interesting asteroid is passing us currently as it does every four years. It is an irregular lump measuring about 3 miles in one direction and 1.5 miles in the other and will only be visible in telescopes. It is called Toutatis and is named after a god of ancient Gaul. Apparently, in some contemporary French cartoons and comic books, a village chief prays to Toutatis to keep the sky from falling. It seems to work! Toutatis will pass Earth at a distance of about 4.3 million miles on the night of December 11-12. In 2004 its closest approach was about 1 million miles. The asteroid’s orbit is affected by the gravitational pull of both Earth and Jupiter. Calculations show that Earth is safe for at least the next six centuries and Toutatis is more likely eventually to be ejected from the solar system than to crash into Earth. Rest easy.

Clear Skies!

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