Thursday, September 27, 2012

The Ellensburg sky for the week of 9/29/12

Saturday: Tonight’s full moon is in the constellation. This morning’s other Moon is…. Wait a minute. The Earth has only one Moon. True. And it has always had only one Moon. Not necessarily true. According to the best existing model, about four billion years ago, a Mars-sized object collided with the young Earth. The resulting debris coalesced to form the Moon. However, this model left a mystery: why is the Moon so asymmetric? Hardened-lava lowlands dominate the near side while the far side is dominated by mountainous highlands. According to a recent revision of the prevailing model, the early collision formed a large Moon and a small Moon. Over the years, the small Moon caught up to and collided with the large Moon. The highlands are the material from the collided small Moon. For more information about this theory, go to

Sunday: Mnemonics are helpful for remembering astronomy facts. (Similarly, “Johnny Mnemonic”, the 1995 cyberpunk film, was helpful in getting Keanu Reeves’ career going.) After all, school children all around the country are learning the order of the planets by remembering, “My very excellent mother just served us nine….” Oops, I guess that one needs updating. Well, here’s one that will not need updating for nearly 100,000 years: the order of the stars in the Big Dipper. Because the nighttime stars are so far away from us, their actual motion through the sky, called their “proper motion” is not noticeable over even thousands of years. That is why the constellations have remained the same since ancient times. But two stars in the Big Dipper have a proper motion large enough such than in 100,000 years, the stars will no longer make a dipper shape. Until then, you can remember the names of the seven dipper stars in order from handle to cup by remembering this helpful advice for teens: “AM, ask mom. PM, dad”. The stars are Alkaid, Mizar, Alioth, Megrez, Phad, Merek, and Duhbe. The Big Dipper is one fist held upright and at arm’s length above the north horizon at 11 p.m.

Monday: Scandalous! The goddess of love will be cozying up to the little king. Venus will be about a pinky-width or less from the bright star Regulus, whose name mean “little king” in Latin. At 6:30 this morning, Regulus will be just to the lower left of Venus, three fists above the east horizon. Because Venus is so close to the Earth, it moves an easily noticeable amount in the sky each day. Compare its position to that of Regulus for the next few days.

Tuesday: The smoke is starting to clear so we can see objects in the sky better than we could a few weeks ago. Luckily the Big Bear Solar Observatory in California doesn’t have this problem. Astronomers have improved the optics of the telescope so much that it is able to resolve features on the surface of the Sun that are just a few miles across. Remember, never look at the Sun without proper eye protection. Instead, go to for images of the Sun and more information about the telescope.

Wednesday: Mars is less than a fist above the southeast horizon at 7:30 p.m.

Thursday: At 10:30 p.m., Jupiter is about one fist above the east-northeast horizon.

Friday: The constellation Orion is four fists above the south horizon at 6 a.m. The Orion is a cloud of gas and dust visible with binoculars about a half a fist below the “belt” of three stars. If you are feeling especially attracted to the nebula, that might be because astronomers think there may be a black hole in the middle. They have not directly observed the back hole, which would be the closest known one to Earth at a distance of 1,300 light years. But the motion of stars in the region is consistent with them being near a black hole 100 times the mass of the Sun. For more information, go to

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

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