Wednesday, December 15, 2010

The Ellensburg sky for the week of 12/18/10

This week, we’ll all be reminded of the lyrics of the song Bonnie Tyler almost sang, Total Eclipse of the Moon. “Turn around. Twice a year I move into the shadow of Terra and I become very dark. Turn around. Five years out of ten I get a little bit tired of becoming red like blood from a shark.”

Saturday: Jupiter is four fists held upright and at arm’s length above due south at 6 p.m. It is by far the brightest point of light in the sky visible at this time.

Sunday: Aldebaran, the brightest star in the constellation Taurus, is about a fist to the lower right of the Moon at 7 p.m.

Monday: Tonight’s moon is full. Ho hum. A full moon happens every month. But, this month, the moon is very close to being in the same plane as the Earth and Sun. Not ho hum. That means there will be a lunar eclipse tonight. Even less ho hum. It will be a total lunar eclipse. Total lunar eclipses are not as obvious as total solar eclipses because light still reaches the Moon even when it is completely blocked by the earth. That is because the Earth’s atmosphere acts like a lens and bends rays of light that would normally miss the moon towards the moon. That doesn’t mean the moon looks the same during a total lunar eclipse as it does during a normal full moon.
Sunlight is white. White light is the sum of all of the colors in the visible spectrum (red, orange, yellow, green, blue, indigo and violet). Our atmosphere scatters the blue component of the Sun’s white light. That is why our sky is blue. (If our atmosphere consisted of different gasses, we would likely have a different colored sky.) When the Sun or moon is near the horizon, the light passes through a lot of the atmosphere meaning a lot of the blue light is scattered and the Sun or moon looks redder than when it is high in the sky. During a total lunar eclipse, sunlight passes through a large slice of the Earth’s atmosphere. The remaining light that reaches the moon is reddish. Thus, the moon looks red during a total lunar eclipse.
From our perspective in central Washington, the moon will begin the partial eclipse stage at 10:32 p.m. The moon will slowly move into the Earth’s shadow and get dark from left to right. At 11:40 p.m., the moon will be fully eclipsed. The total eclipse lasts until 12:52 a.m. The moon will be moving out of the earth’s darkest shadow or umbra until 2:00 a.m. After that, the moon will look white just like a normal full moon. Thus, during the entire eclipse, the moon looks white, then black, then red all over. For more information, go to NASA’s eclipse website at

Tuesday: At 3:43 p.m., the Sun reaches its lowest point in the sky with respect to the background stars. This point is called the Winter Solstice. During the day that the Sun reaches this point, your noon time shadow is longer than any other day of the year. Also, the Sun spends less time in the sky on the day of the Winter Solstice than any other day making this the shortest day of the year. Even though it is the shortest day of the year, it is not the day with the latest sunrise or the earliest sunset. The latest sunrise is during the first week in January and the earliest sunset is during the second week in December. The Sun is at its southernmost point with respect to the background stars on the day of the winter solstice. This means the Sun spends the least amount of time above the horizon on that day. But, the Sun rise and set time depends on more than its apparent vertical motion. It also depends on where the Sun is on the analemma, that skinny figure-8 you see on globes and world maps. During the second week in December, the Sun is not quite to the bottom of the analemma. But, it is on the first part of the analemma to go below the horizon. During the first week in January, it is on the last part of the analemma to rise above the horizon. For more information on this, go to

Wednesday: Venus is two and a half fists above the southeast horizon. It is by far the brightest point of light in the sky visible at this time. Yes, I know I wrote this about Jupiter. Venus is brighter than Jupiter but it is not above the horizon in the evening this month.

Thursday: I know you’re staying up late to train yourself to wait up for Santa. So look out a south-facing window at 1 a.m. and see Sirius, the brightest star in the nighttime sky, as high as it ever gets in the sky. It is two and a half fists above sue south.

Friday: What would that special someone want to see on the back of Santa’s sleigh when she gets up early Christmas morning to eat one of Santa’s cookies? A fruit cake? No. A barbell? Maybe to work off the fruitcake. A subscription to The Daily Record? Of course. But what she really wants is a ring. And if she looks out a south-facing window, she’ll see her ring. Saturn the ringed planet, that is. Saturn is nearly four fists above the south horizon at 6:30 a.m.

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

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