Wednesday, December 5, 2012
The Ellensburg sky for the week of 12/8/12
Saturday: The earliest sunsets of the year occur all this week – 4:13 p.m. That seems counterintuitive because the shortest day of the year in the Northern Hemisphere isn’t until December 21. Since the Earth’s orbit is elliptical, the Sun does not appear to move across the sky at the same rate from day to day throughout the year. That means some parts of the year the Sun is “fast” and sometimes “slow”. Today, the Sun reaches the noontime position of due south at 11:52 a.m. meaning it will also reach the setting position a few minutes earlier than the expected time. For more information on this, go to http://goo.gl/kjnHP. Or just go watch the sunset. But don’t stare at the Sun.
Monday: Okay boys and girls. Let’s follow along with the moon this week as it tours the bright objects in the southeastern sky. At 6:30 a.m., the bright star Spica is less than a half a fist above the moon. Spica is believed to be the star that provided the ancient astronomer Hipparchus with the data to show that the Earth precesses like a spinning, wobbling top.
Tuesday: On these cold mornings, it is difficult to get going. You just want to plop into a chair and sit still. But, are you really sitting still? You’re moving at about 700 miles per hour due to the rotation of the Earth on its axis and 66,000 miles per hour due to the revolution of the Earth around the Sun. If that’s not enough, the entire solar system is orbiting the center of the galaxy at a whopping 480,000 miles per hour! So while you may be sitting still with respect to your living room (and all of the over achievers in your house), you are NOT sitting still with respect to the center of the galaxy. For more information about this concept, go to http://goo.gl/lPVPS. Before you barf from all of that motion, go outside at 6:30 a.m. and observe Saturn, less than a fist above the moon in the southeast sky. Because of Saturn’s rapid rotation, only 10.5 hours, it appears visible flattened.
Tuesday: At 6:30 this morning, the moon marks the right angle corner of a right triangle with the very bright Venus above it and Mercury to its lower left.
Wednesday: Just like during last month’s new moon, people are humming the astronomy version of 1981 Blondie hit The Tide is High: “The tide is high ‘cause the moon is new. Higher still when the moon’s close, too.” Tonight's moon is new. The new moon is the phase where the Moon is directly between the Earth and the Sun. That means the moon and Sun are both stretching the Earth in the same direction causing the ocean water in line with the Sun and moon to be pulled upward. In addition, the moon is at perigee so this is the day of the month when the moon is closest to the Earth. This accentuates the upward pull on the water and makes the tides really high.
Thursday: The Geminid meteor shower peaks late tonight and early tomorrow morning. Meteor showers are named after the constellation from which the meteors appear to originate. These meteors appear to come from a point in Gemini the twins. This point is about three fists held upright and at arm’s length above the east-northeast horizon at 9 p.m. tonight. You can follow this point throughout the night, as it will remain near the bright star Castor, the right hand star of the “twin” stars Pollux and Castor. This shower is typically one of the best ones of the year producing bright, medium speed meteors with up to 80 meteors per hour near the peak. This year, the moon will be new during the peak night ensuring dark skies.
Most meteor showers occur when the Earth passes through the orbital trail of a comet. The broken off comet fragments collide with the earth and burn up in the atmosphere. Astronomers had searched for a comet source for this shower since 1862 when the shower was first observed. Finally, in 1983, astronomers discovered the object that created the fragments that cause the meteor shower. To their surprise, it was a dark, rock that looked like an asteroid, not a shiny icy comet. Astronomers named this object Asteroid 3200 Phaethon. But, they still don’t know if it an asteroid or if it is a comet with all of its ice sublimated away by many close passes by the Sun. For more information about 3200 Phaethon, go to http://goo.gl/LuwGW.
Friday: Mars is less than a fist to the left of the thin crescent moon, low in the southwest sky.
The positional information in this column about stars and planets is typically accurate for the entire week.