The Ellensburg WA sky for the week of 6/25/16

Saturday: “Mom, I can’t sleep. It is too light out!” A poor excuse you say? Good astronomy skills, I say. The latest sunset of the year happens this week. Surprisingly, the earliest sunrise and the latest sunset do not both happen on the longest day of the year, the day of the summer solstice. The earliest sunrise occurs just before the longest day and the latest sunset occurs just after the longest day. This phenomenon relates to the angle of the Sun’s path near rising and setting. In Ellensburg, that angle is about 66 degrees near the first day of summer. Because of the Earth’s orbit, which causes the Sun’s apparent motion, the angles are not symmetric. The asymmetries in orbital angles leads to the asymmetry in rise and set times. By the way, picking a specific night to give you the “can’t sleep because it is too light out” line may just be an excuse because the sunset times change by only a few seconds each day in June. This year, the sun sets between 9:01 and 9:02 p.m. between June 21 and July 2.

Sunday: Jupiter is about two fists held upright and at arm’s length above the west-southwest horizon at 10 p.m.

Monday: Don’t wait until a week from today to go to those wimpy firecracker shows. Find the hypergiant star Rho Cassiopeiae. Astronomers think that Rho Cassiopeiae will likely go supernova (explode) in the near future. Of course, for stars, near future might mean today. It might mean 20,000 years from now. Rho Cassiopeiae is in the constellation Cassiopeia the queen. At 11:00 tonight, Cassiopeia looks like the letter “W” about three fists held upright and at arm’s length above the northeast horizon. Rho Cassiopeiae is about a finger’s width to the right of the rightmost star in the “W”. Once you find it you’ll be thinking, “Big deal, I can hardly see it.” Although it is barely visible to the naked eye, it is actually very bright. It is the 20^th most luminous star in the sky, a whopping 550,000 times more luminous than the Sun.

Tuesday: Mars is two fists above due south at exactly 9:51 pm. The bright reddish star Antares is one and a half fists above due south at exactly 11:01 pm. Saturn is two fists above due south at exactly 11:00 pm. I love formulaic writing.

Wednesday: Star light. Star bright. The first star you see tonight might be Arcturus, six fists above the south horizon right after sunset. You’ll be able to see either Jupiter or Mars earlier but they won’t facilitate your wish coming true.

Thursday: Happy Asteroid Day (http://www.asteroidday.org/), the day we celebrate avoiding the destruction of the Earth by an undiscovered asteroid. There are a million asteroids in the Solar System with the potential to strike Earth and destroy a city. Astronomers have discovered only 1% of them. Asteroid Day is an effort to educate the public and encourage policy makers to fund this important effort. King Tut may have celebrated an ancient Asteroid Day by asking his assistants to make a dagger out of a broken-off asteroid that landed on Earth. Astronomers discovered that the blade of the knife contained much more nickel than is found in terrestrial iron, an amount consistent with iron meteorites, especially with one found 16 years ago in northern Egypt. For more information about the dagger, go to http://goo.gl/BHBivd.

Friday: Mizar is a well-known binary star in the constellation Ursa Major. You can find it at the bend in the Big Dipper handle, nearly straight overhead at 10 p.m. tonight. Its name is Arabic for waistband. Mizar has an optical double called Alcor, which is less than a pinky width away and can easily be seen with the naked eye. Optical doubles are stars that are close together in the sky but do not orbit a common center of mass as true binary stars. Not wanting to deceive sky gazers who call Mizar a binary star, two stars that DO orbit a common center of mass, Mizar actually is a binary. It was the first binary star system discovered by telescope. Mizar A and Mizar B are about 400 astronomical units apart from each other and about 80 light years from Earth. 400 astronomical units is about 10 times the distance between the Sun and Pluto.

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.