Wednesday, May 13, 2015

The Ellensburg WA sky for the week of 5/16/15

Saturday: The questions who, what, where, and when can only be asked with a “W”. At 11 p.m., the W-shaped constellation Cassiopeia is about two fists held upright and at arm’s length above due north. The middle star in the W was used as a navigation reference point during the early space missions. The American astronaut Gus Grissom nicknamed the star Navi, his middle name Ivan spelled backwards. After he died in the Apollo 1 fire, the star name was kept as a memorial.

Sunday: NASA’s Dawn space probe is closing in on the largest asteroid, Ceres. While it is important to send spacecraft to explore the asteroid belt, sometimes asteroid parts come to us. The light that bounces off the second largest asteroid 2 Pallas shows it is made of the same material as some rare dark stony meteorites that show signs of being altered by contact with water. These meteorites may have broken off 2 Pallas or a similar asteroid during the early Solar System. Go to for more information on 2 Pallas. For the next two months, 2 Pallas is in the constellation Hercules, visible with large binoculars or a small telescope.

Monday: In an old Saturday Night Live spoof advertisement for a turkey you can pump (, Chris Rock sang, “The first turkey dinner was 1620. The pilgrims had it in the land of plenty.” But he could have just as easily say, “The light left Rasalgethi in 1620. The light now reaches us in the land of plenty.” Rasalgethi is a double star in the constellation Hercules that is almost 400 light years away. Its name is based on the Arabic words meaning “Head of the kneeler” because some views of Hercules depict him as a warrior kneeling down, perhaps resting after his twelve labors. You’ll find Rasalgethi exactly two fists above due east at 9:40 p.m.

Tuesday: Altair is about a half a fist above the east horizon at 11 p.m.

Wednesday: Give me an “M”. Give me a “3”. What does that spell? “M3.” “Big deal,” you say. It was a big deal to French comet hunter Charles Messier (pronounced Messy A). M3 was the 3rd comet look-alike that Messier catalogued in the late 1700s. M3 is a globular cluster, a cluster of over 100,000 stars that is 32,000 light years away. It is too dim to be seen with the naked eye but is fairly easy find with binoculars. First find Arcturus six fists above the southeast horizon at 11 p.m. Move your binoculars up a little so two stars of nearly identical brightness are in your field of view. When the top star is in the lower left part of your field of view, there should be a fuzzy patch near the center of your field of view. This is M3.

Thursday: Venus is about a fist to the upper right of the Moon at 10 p.m. In two nights, the Moon will have moved to be a little more than a half a fist underneath Jupiter.

Friday: Saturn is opposition tonight. That doesn’t mean that Saturn is a teenager. Opposition means that Saturn 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. Saturn is about two and a half fists above due south at 1 a.m. It is about one fist above the southeast horizon at 10 p.m.
If you remember this column from 2/23/2008, 3/8/2009, 3/21/2010, 4/4/11, 4/15/12, 4/27/13, and 5/11/14, you know that Saturn was also in opposition on those dates. Thus, it is in opposition about 12 days later each year. 12 days is about one thirtieth of a year. This implies that it takes Saturn about 30 years to make one orbit around the Sun and get back in line with the same stars again. Saturn’s actual orbital period of 30 years matches this approximation very well.

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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