Wednesday, December 23, 2015
The Ellensburg WA sky for the week of 12/26/15
Saturday: When the Moon is full or close to full, it is difficult to see dim objects in the sky because of the sky glow. But why struggle to find dim objects when there is so much to see on the big, bright object in front of you? The lunar crater called Tycho is best seen during a full Moon. Tycho was formed about 109 million years ago when an asteroid struck the Moon, leaving a crater over 50 miles in diameter and ejected dust trails that radiate out hundreds of miles in all directions. For more lunar highlights, go to http://nightsky.jpl.nasa.gov/docs/ObserveMoon.pdf, a resource of the Night Sky Network.
Sunday: You’ve heard the term “a pinch to grow an inch.” Well, Jupiter’s extremely strong gravitational field “pinches” Jupiter so much that it causes Jupiter to shrink by about an inch a year. Look for the svelte Jupiter one fist held upright and at arm’s length above due east at midnight.
Monday: You’ve heard the term “a pinch to grow an inch.” Come on. Now I know you have. While there is no pinching involved, the distance between the Earth and moon increases by about an inch a year. Does it look farther tonight than when you looked at it on Saturday? It’s 2/365ths of an inch farther from the Earth.
Tuesday: Hit the road Mercury. And don’t you come back no more, no more. For a few weeks, Mercury has been hitting the road and moving away from the Sun in the sky. Today, Mercury is as far away from the Sun as it will get on the evening half of this cycle. This is known as its greatest eastern elongation. Yet, this distance does not translate into good viewing because Mercury will be very low in the sky. Mercury is about a half a fist above the southwest horizon at 5 p.m. Over the next few weeks, Mercury will move toward the Sun in the sky. After it passes in front of the Sun, it will appear in the morning sky by the end of January.
Wednesday: At 7:30 a.m., Saturn is one fist above due southwest. The much brighter Venus is a fist to the upper right of Saturn. The reddish planet Mars is about three fists above the south horizon.
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. That perennial favorite New Year’s Day marker, Sirius, the brightest star in the night sky, 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.
And while you are up, grab those binoculars and look for Comet Catalina right next to the bright star Arcturus throughout the night. Arcturus and Catalina rise in the east-northeast sky just after midnight. By 3 a.m., they are three fists above due east. By 6 a.m., they are two and a half fists above the southeast horizon.
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. The International Astronomical Union promoted Ceres to the status of “dwarf planet” in August of 2006.
The positional information in this column about stars and planets is typically accurate for the entire week. For up to date information about the night sky, go to http://nightsky.jpl.nasa.gov/planner.cfm.