The Ellensburg sky for the week of 5/24/14

Saturday: Hit the road Mercury. And don’t you come back no more, no more. For a few weeks, Mercury has been hitting the road and moving away from the Sun in the sky. Today, Mercury is as far away from the Sun as it will get on the evening half of this cycle. This is known as its greatest eastern elongation. Yet, this distance does not translate into good viewing because Mercury will be very low in the sky. Mercury is about a half a fist held upright and at arm’s length above the west-northwest horizon at 9:30 p.m. Over the next few weeks, Mercury will move toward the Sun in the sky. After it passes in front of the Sun, it will appear in the morning sky by the beginning of July.

Sunday: The crescent moon and Venus hang out together in the early morning sky. Venus is about a thumb width below the moon, low in the eastern sky at 4:30 a.m. I you don’t want to get up early, the evening sky has plenty of planets. Jupiter is two fists above the west horizon at 9:30 p.m.

Monday: Late spring and early summer is a good time to look for star clusters. Last week, you learned about M3, the third object cataloged by French astronomer Charles Messier over 200 years ago. One of the best clusters is the globular cluster in the constellation Hercules, also called M13. (Hummm. Guess what number that object is in Messier’s catalog.) Globular clusters are compact groupings of a few hundred thousand stars in a spherical shape 100 light years across. (For comparison, a 100 light year diameter sphere near out Sun would contain a few hundred stars.) The globular cluster in Hercules is six fists above the east horizon at 11 p.m. First find Vega, the bright bluish star about four fists above the east-northeast horizon. Two fists to the upper right of Vega is a keystone shape. Aim your binoculars at the two stars that form the uppermost point of the keystone. The globular cluster is one third of the way south of the uppermost star on the way to the rightmost star of the keystone. It looks like a fuzzy patch on the obtuse angle of a small obtuse triangle. If you don’t know what an obtuse angle is, you should not have told your teacher, “I’ll never need to know this stuff”.

Tuesday: The constellation Aquila the eagle is starting its migration across the summer evening sky this month. Aquila, marked by its bright star Altair, rises to one fist above the east horizon at 11 p.m. Not all animal migrations are fully understood by scientists. We might be inclined to attribute bird migrations to instinct. This answer certainly did not satisfy the theologian C. S. Lewis. In his short work “Men Without Chests”, he wrote, “to say that migratory birds find their way by instinct is only to say that we do not know how migratory birds find their way”. In science (and theology), Lewis is telling us to look for real causes and not simply labels such as instinct. The cause for Aquila’s migration is the Earth orbiting the Sun. As the Earth moves around the Sun, certain constellations move into the evening sky as others get lost in the glare of the setting Sun.

Wednesday: Cygnus the swan flies tonight. Deneb, the brightest star in the constellation, whose name means “tail” in Arabic, is two fists above the northeast horizon at 10 p.m. Cygnus’ wings make a vertical line one half a fist to the right of Deneb. Its head, marked by the star Albireo, is two fists to the right of Deneb. While Deneb is at the tail of Cygnus, it is at the head of the line of bright stars. It is 160,000 times more luminous than the Sun making it one of the brightest stars in the galaxy. It does not dominate our night sky because it is 2,600 light years away, one of the farthest naked eye stars. If Deneb were 25 light years away, it would shine as bright as a crescent moon. Compare that to Vega, which is 25 light years away. Vega is three and a half fists above the east-northeast horizon at this time.

Thursday: Good night little doggie. Procyon, the brightest star in Canis Minor, the little dog, is less than one fist above the west horizon at 10 p.m. Over the next couple of weeks, it will be too close to the setting Sun in the sky to be visible.

Friday: At 11 p.m., Mars is three fists above the southwest horizon and Saturn is three fists above the south horizon.

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.