The Ellensburg sky for the week of 12/17/11

What's up in the sky 12/17/11

Today: Listen, do you want to know a secret? Do you promise not to tell? Whoa oh, oh. The Beatles certainly didn’t write this song about the Barringer meteorite crater in Arizona. Astronomers are studying this 50,000-year-old impact to learn more about our planet’s violent history as well as the physics of impacts throughout the solar system. If you’d like to be let in on some of these secrets, go to http://goo.gl/sqbBe.

Sunday: This morning’s Moon is nearly in the third quarter phase, the phase that occurs when the Sun, Earth, and Moon make a right angle and the left side of the Moon appears illuminated. I wrote “nearly” because the three objects make a right angle at 5 p.m. this evening, when the Moon is not even visible in Washington. It is visible about four fists above the southwest horizon at 7 a.m. Mars is one fist above the Moon.

Monday: Venus is one fist above the southwest horizon at 5 p.m.

Tuesday: Jupiter is five fists above due south at 8 p.m.

Wednesday: At 9:30 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 http://goo.gl/wE9nP.

Thursday: I know you’re staying up late to train yourself to wait up for Santa. So look out a south-facing window at 12:45 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 due south.

Friday: Mercury will be as far away from the Sun in the sky as it will get this orbital cycle. This "farthest away" point is known as the planet's greatest elongation. Since Mercury is in morning sky, it is west of the Sun and this occurrence is called the greatest western elongation. This morning and tomorrow morning will be the best mornings to observe Mercury for the next few weeks. Mercury is about a fist above the southeast horizon at 7 a.m. Over the next few weeks, Mercury will move toward the Sun in the sky. By late February, it will be visible in the evening sky.

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