Thursday, April 23, 2015

The Ellensburg WA sky for the week of 4/25/15

Saturday: Tonight’s first quarter moon makes a right triangle with the Beehive Cluster and Jupiter. Since it is so close to the Moon in the sky, you’ll need binoculars to see the Beehive Cluster. First find the Moon at 10 p.m. Then look about a half a fist held upright and at arm’s length to the upper right of the Moon. The other corner of the triangle, Jupiter, is about a fist to the upper left of the Moon.

Sunday: Mercury is a half a fist above the west-northwest horizon and Venus is two and a half fists above the west horizon at 9 p.m.

Monday: Saturn is a half a fist above the southeast horizon at 11 p.m.

Tuesday: Do people think you have a magnetic personality? The star Cor Caroli understands how you feel. Cor Caroli has one of the strongest magnetic fields among main sequence stars similar to our Sun. This strong magnetic field is thought to produce large sunspots that cause the brightness of Cor Caroli to vary. Cor Caroli is nearly straight overhead at 11:30 p.m.

Wednesday: You know Metis and Thebe and Adrastea and Amalthea. Io and Ganymede and Callisto and Europa. But do you recall? There are 67 Jovian moons in all. (As of July 2013.) Just 60 years ago, Jupiter was thought to have only 12 moons. But, astronomers are red-nosed with delight that the advent of supersensitive electronic cameras has caused the number of discovered moons to rapidly increase. Jupiter’s 67 moons range in size from Ganymede, with a diameter of 5,262 kilometers, to S/2002 J12 and S/2003 J9, with a diameter of only one kilometer. Our moon has a diameter of 3,475 kilometers. (One kilometer is 0.62 miles.) Saturn is second place in the moon race with 62. Uranus is next with 27. Then comes Neptune with 14, Mars with 2, and Earth with 1. Even dwarf planets have moons. Pluto has 5, Eris has 1, and Haumea has 2. Eris is an outer solar system object that was discovered in 2005 and named in September of 2006. Because astronomers thought it was larger than Pluto, people called it the tenth planet for a while. (More recent measurements show Eris to be a little smaller than Pluto.) Haumea, the newest dwarf planet with a moon, was discovered in 2004 and officially named a dwarf planet on September 17, 2008. Jupiter, the “mooning” champ, is four fists above the west horizon at 9 p.m. Go to for more information about Solar System moons.

Thursday: Avast ye matey. Swab the poop deck. Pirates love astronomy. In fact, the term “poop” in poop deck comes from the French word for stern (poupe) which comes for the Latin word Puppis. Puppis is a constellation that represents the raised stern deck of Argo Navis, the ship used by Jason and the Argonauts in Greek mythology. Argo Nevis was an ancient constellation that is now divided between the constellations Puppis, Vela and Carina. The top of Puppis is about a fist and a half to the left of the bright star Sirius in the south-southwest sky at 9 p.m. Rho Puppis, one of the brightest stars in the constellation, is about one and a half fists above the south-southwest horizon at this time.

Friday: Winter must be over because the winter constellations are becoming less visible. Orion is setting in the west starting at about 9 p.m. At this time, Orion’s belt is a little more than half a fist above the west horizon and Betelgeuse is nearly two fists above the west horizon. By mid-May, Orion will be lost in the glare of the Sun.

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

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