The Ellensburg sky for the week of 6/23/12

Saturday: Don’t wait until the 4^th of July 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.

Sunday: Go outside and find the bright star Regulus, about a fist to the right of the Moon at 11 p.m.

Monday: Mars is less than a fist above Moon at 11 p.m. Since you also observed that the Moon was near Regulus last night…. You did observe the Moon last night, didn’t you? I asked you to. A civilized society thrives because its people honor the reasonable requests made by others. If you just say “yes” and ‘no” whenever you feel like it, human interactions grind to a halt. Okay, enough with the guilt trip. Back to astronomy. Since you also observed that the Moon was near Regulus last night, you can approximate how far it appeared to move. It moved a little more than one fist. Since one fist held at arm’s length subtends an angle of 10 degrees. The Moon moved about 13 degrees through the sky. In 28 days, the Moon will have moved about 360 degrees (13 degrees/day X 28 days). 360 degrees brings it back to where it started. Thus, making one simple measurement, how far the Moon moves through the sky in one day, you can determine the length of the lunar cycle.

Tuesday: “If you don’t maneuver more carefully, we are going to crash.” How often do you hear that while driving? Well, the Milky Way Galaxy is going to hear that a lot over the next four billion years. After carefully analyzing the motion of the Andromeda Galaxy, astronomers have determined that the Andromeda and the Milky Way are on a collision course. To locate the Andromeda Galaxy before it ends up in your backyard, first find the Great Square of Pegasus. At midnight, the left hand corner of the square is about one fist above the east-northeast horizon. Less than two fists to the left and down a little bit is another star the same brightness as the star at the corner of the square. From that star, hop about a half a fist up to a star that is about one fourth as bright. Less than another half fist in the same direction is a fuzzy oval patch of light known as the Andromeda Galaxy. The galaxy is impressive to see in binoculars. It consists of about 400 billion stars and is 2.2 million light years away. Go to http://hubblesite.org/newscenter/archive/releases/2012/20/ to read more about the upcoming collision.

Wednesday: The bright star Spica is about a half a fist to the upper left of the Moon at 10 p.m. Saturn is about a half a fist above Spica.

Thursday: Jupiter is one fist above the east-northeast horizon at 4:30 a.m. The much brighter Venus is a half a fist below Jupiter.

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.