The Ellensburg WA sky for the week of 4/23/16

Saturday: Ah, the signs of spring. Trees budding. Flowers blooming. Young lovers frolicking. The Spring Triangle rising. In order of brightness, Arcturus, Spica, and Regulus form a triangle that rises as the Sun is setting. By 9 a.m., Regulus is five fists held upright and at arm’s length above due south, Spica is one and a half fists above the southeast horizon, and Arcturus is three fists above the east horizon. For the next few months, Jupiter joins the triangle, five fists above the south-southeast sky.

Sunday: Are you thirsty when you get up in the morning? If so, that’s okay because the Big Dipper is positioned to hold water in the morning sky. Look three fists above the northwest horizon at 5 a.m. You’ll see three stars that make a bent handle and four stars that make a cup.

Monday: There’s a trapezoid in the early morning south-southeast sky about one and a half fists above the horizon. In order of brightness, the Moon, Mars, Saturn, and the star Antares mark the corners of a four-sided figure with two parallel sides. Antares and Saturn make up the lower left-hand side. Mars and the Moon, the upper right side. Follow them over the next hour as the Sun starts to rise. Determine how bright the sky can be before you can no longer see Mars.

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. Go to http://goo.gl/Xkoeq for more information about Solar System moons.

Thursday: Its two small moons, Phobos and Deimos, are not visible in typical backyard telescopes. But they are an interesting study. The prevailing view among most astronomers is that they are captured asteroids. That makes sense given Mars’ proximity to the asteroid belt. But resent findings by European astronomers indicate that Phobos is very porous and made of material similar to the surface of Mars. This implies that Phobos may consist of chunks of Martian debris that was blasted off by numerous impacts and gravitationally bound together. Unfortunately, the Russian Phobos-Grunt probe launched late 2011 to collect material from Phobos crashed to Earth after malfunctioning. For more information about this new model of Phobos’ formation, go to http://goo.gl/8sw3rM.

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 http://nightsky.jpl.nasa.gov/planner.cfm.