Wednesday, September 27, 2017
The Ellensburg WA sky for the week of 9/30/17
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: Venus and Mars are about a pinky width apart, one and a half fists above the east horizon at 6:30 a.m. That’s pretty close. But, they will get closer later in the week. By Thursday morning, they’ll be less than the apparent diameter of the full Moon apart from each other.
Monday: Say “good bye” to Jupiter because it will soon be lost in the glare of the Sun for a few weeks. It is less than a half a fist above the west-southwest horizon right after sunset.
Tuesday: Since Halloween is later this month; the stores are filled with bags of candy clusters. Instead, take time to look at a star cluster. The Hyades cluster is an open star cluster that represents the V-shaped face of Taurus the bull. It is one of the biggest and nearest star clusters with about 200 stars 150 light years away. The Hyades cluster was the first cluster to be the subject of detailed motion studies. These studies allowed astronomers to pinpoint the distance to the Hyades and provide important information about the scale of the universe. Aldebaran, nearly two fists held upright and at arm’s length above the east horizon at 11 p.m., is a foreground star and not a part of the Hyades cluster.
Wednesday: Speaking of good byes, NASA said “good bye” to the Cassini spacecraft earlier this month. This picture (https://stardate.org/astro-guide/gallery/saying-goodbye) shows Cassini saying “good bye” to the moon Enceladus as it plunges into Saturn’s atmosphere. Say “Hello” to Saturn at 7:30 tonight, one and a half fists above the south-southwest horizon.
Thursday: Get up at 6:30 a.m., dig a dime out of your piggy bank, and hold it out at arms length, one and a half fists above the east horizon. You’ll be able to block both Mars and Venus at the same time. That’s how close together they are in the sky. Winter is coming to the morning sky. The “winter constellations” such as Orion, Taurus, and Gemini are high above the southern horizon at 6:30 a.m. They are called winter constellations because they are high in the sky during the evening viewing hours of the winter months.
Friday: 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.
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 https://nightsky.jpl.nasa.gov/planner.cfm.