Riding A Cosmic Carousel


Bob King / News Tribune

Another cold, clear night last night. The coyotes yipped and a few trees popped loudly as the temperature dropped to 12 below. Heat absorbed during the day quickly radiates away on a clear night making wintertime star gazing a challenge.

Yesterday we looked at the rising and setting of stars due to Earth’s rotation. Our planet also revolves around the sun in an orbit that takes one year. This movement causes the stars to slowly drift westward night after night. The drift isn’t much — only one moon diameter per day. But it really adds up over time. Stand outside the next clear night and line up a familiar star up with a power pole or rooftop. Stand in that spot a week later at the exact same time and you’ll immediately notice that your star has scooted westward compared to the week before.

The illustration above shows that we face Orion on winter nights but leave him behind by late March. His place is soon taken by Leo. And by the time May’s flowers brighten the forest, our view of the night sky will face Scorpius the Scorpion. It’s as if we’re on an amusement park carousel, watching the mini donut stands and midway games pass by in their turn as we cycle ’round and ’round.

Orion will be lost in the glare of the sun for several months during summer and re-emerge in August in the morning sky. Not until our "carousel horse" the Earth has come full circle will Orion once again mount into the winter skies.