Friday, September 27, 2013
The Ellensburg sky for the week of 9/28/13
Saturday: 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.
Sunday: To the people of Ancient Greece, the stars that are about five and a half fists above the east-northeast horizon at 10 p.m. were known as Cassiopeia and Andromeda, a mythological queen and her daughter. But not all cultures imagined the same pictures in the sky. To the people of Polynesia, the stars of Cassiopeia and Andromeda represented a dolphin, called Kwu. Cassiopeia formed its tail, the brightest stars of Andromeda formed its fins, and its fainter stars outlined the dolphin’s body.
Monday: Three planets are crowded around the setting Sun. Venus, the brightest, is one fist above the southwest horizon. Saturn is about a fist and a half to the right of Venus. Mercury is below Saturn, just barely above the horizon.
Tuesday: Uranus is in opposition tonight. That doesn’t mean that Uranus is in the minority party in the senate. Opposition means that Uranus is on the opposite side of the Earth as the Sun. When an object is in opposition, it is at its highest point in the sky during the darkest time of the day. Thus, opposition is typically the best time to observe a planet. Uranus is about four and a half fists above the south horizon at 1 a.m. It is three and a half fists above the southeast horizon at 10:30 p.m. You’ll need binoculars to find it. First find Deneb Kaitos, the brightest star in the constellation Cetus the sea monster, one and a half fists above the southeast horizon. Deneb Kaitos is the same brightness as the North Star. If you imagine the distance from the horizon to Deneb Kaitos as one unit, move your binoculars straight up from southwest two more of those units. Uranus will be in the center of your field of view. Check that same spot over the next few night. Uranus will move slightly with respect to the distant stars.
Wednesday: Mars is about to get eaten by a lion, a constellation lion. It is right in front of the head of Leo the lion, three fists above the east horizon at 6 a.m.
Thursday: Keep an eye out for Jupiter which is slowly creeping into the pre-midnight sky. Tonight it rises at about 11:45 p.m. By 12:30, it is a half a 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 http://goo.gl/AGjFf.
The positional information in this column about stars and planets is typically accurate for the entire week.