Thursday, May 19, 2016
The Ellensburg WA sky for the week of 5/21/16
Saturday: 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. (. 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 held upright and at arm's length 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”.
Sunday: Mars is at opposition tonight. No, that doesn’t mean that Mars refuses to eat his vegetables. (Please eat your vegetables, children.) Opposition means that Mars is on the opposite side of the Earth as the Sun. An object is in opposition when it is due south 12 hours after the Sun. When an object is in opposition, it is at its highest point in the sky during the darkest time of the night. A planet in opposition shines brighter and appears larger in a telescope than any other night. And since Mars is also relatively close, it is very bright tonight. Mars is about two fists above due south at 1 a.m. Saturn is one fist to the left of Mars, right next to a bright object called the Moon.
Monday: 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 held upright and at arm’s length 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.
Tuesday: Jupiter is four fists above the southwest horizon at 10 p.m.
Wednesday: Good night little doggie. Procyon, the brightest star in 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.
Thursday: The bright star Capella is one and a half fists above the northwest horizon at 9:30 p.m.
Friday: While the NASA probe Dawn is off exploring the largest main-belt asteroid Ceres, you can explore the second largest asteroid Vesta. NASA has released Vesta Trek, a free web-based application that allows you to zoom in, “fly” over the surface, measure craters sizes, and see what Vesta looks like in different wavelengths of light. Go to http://goo.gl/97NxgF for more information about Vesta Trek and the Dawn mission.
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.