Tuesday, December 22, 2009

The Ellensburg sky for the week of 12/26/09

Saturday: Mars is two fists held upright and at arm’s length above due east at 10 p.m. What does it mean to be “two fists held upright and at arm’s length above due east?” Make a fist with your right hand. Hold it out in front of you at arm’s length. Do you feel like you can “fight the power”? Good. Now, hold your fist vertical so your thumb is on top. The angular distance from the top of your fist to the bottom is 10 degrees. Place the top part of your fist at eye level. This represents zero degrees. Now, stack the left fist on top. The top of this fist is 10 degrees above the horizon. Any celestial object even with the top of your left fist is about 10 degrees above the horizon. If you were to hold your left fist steady and move your right fist on top of the left, the top of the right fist would be about 20 degrees above the horizon.

Sunday: Columbia the dove, representing the bird Noah sent out to look for dry land as the flood waters receded, is perched just above the ridge south of Ellensburg. Its brightest star Phact is about one fist above due south at 11 p.m.

Monday: We end the year with a traditional children’s story, Moon White and the Seven Sisters. Once upon a time, there was a nearly full moon. Even though this moon was actually quite dark, reflecting only about 10% of the light that shined on it, this moon looked as white as snow. Lovers of bright, white objects, there were Seven Sisters who longed to get close to the Moon in the sky. The Seven Sisters were a strange group of girls. In fact, they were not girls at all but an open star cluster consisting of nearly 100 stars. These Seven Sisters or 100 stars or whatever they were went by the name the Pleiades. At 6 p.m., the Pleiades is right above the Moon in the eastern sky. You’ll need binoculars to see the Seven Sisters as they are obscured by the moonlight. (I never said it was an interesting or well-written children’s story.)

Tuesday: Jupiter is about two fists above the southwest horizon at 6 p.m.

Wednesday: Saturn is four fists above the south-southwest horizon at 7 a.m.

Thursday: Forget about that big bright ball in Times Square. You can mark the start of the new year with one of the sky’s own big bright balls: the Moon. Tonight is the second full moon in December. It starts to “fall” from its highest point in the southern sky a little after midnight. Sky watchers in parts of Africa, Asia, and Europe will be able to observe a partial lunar eclipse.
That perennial favorite marker if the new year, Sirius, the brightest star in the night sky, always rises to its highest point in the sky a little after midnight on January 1. Thus, when Sirius starts to “fall”, the new year has begun. Look for Sirius about two and a half fists above due south at midnight.

Friday: Today is the day we celebrate the anniversary of something new – a new classification of celestial objects. Giuseppe Piazzi discovered Ceres [pronounced sear’-ease], the first of what are now called “asteroids”, on January 1, 1801. Ceres is the largest asteroid in the belt between Mars and Jupiter. At first, Piazzi thought it was a star that didn’t show up on his charts. But, he noted its position changed with respect to the background stars from night to night. This indicated to him that it had to be orbiting the Sun. In August of 2006, Ceres got promoted to the status of “dwarf planet” by the International Astronomical Union.

Has it been tough to wake up this past week? It should have been because the sunrise has been getting a little later since summer today. I know. I know. December 22 was the shortest day of the year. But, because the Earth’s orbit around the Sun is elliptical and not circular, the Earth does not travel at a constant speed. It moves faster when it is closer to the Sun and slower when it is farther away. This leads to the latest sunrise occurring in early January and the earliest sunset occurring in early December, not on the first day of winter, the shortest day of the year. On the first day of winter, however, the interval between sunrise and sunset is the shortest.

The positional information in this column about stars and planets is typically accurate for the entire week.

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