Wednesday, September 22, 2010

The Ellensburg sky for the week of 9/25/10

Saturday: “You know Aries and Cancer and Draco and Libra. Leo and Pisces and Virgo and Hydra. But, do you recall, the pointiest asterism of all? Triangulum, the three sided asterism, had a very pointy edge….” Sorry. Some stores have started putting up their Christmas decorations and that has put me in the mood to modify some Christmas songs. Anyway, Triangulum is a small constellation between the more prominent Andromeda and Aries. Its main feature is a skinny triangle oriented parallel to and nearly four fists held upright and at arm’s length above the east horizon at 10 p.m.

Sunday: Venus will really be negative for the next few nights. But, don’t feel bad for Venus. It is okay for a celestial object to be negative as long as we are referring only to its magnitude. The ancient Greek astronomer Hipparchus developed a system for rating the apparent brightness of stars and planets in which lower numbers refer to brighter stars and planets. In his initial scheme, all points of light in the night sky were classified from first magnitude, meaning bright, to sixth magnitude, meaning very dim. Modern day astronomers have made this scale more quantitative. Tonight and tomorrow, Venus has a magnitude, or apparent brightness rating, of -4.6. Sirius, the brightest star in the night sky, has a brightness rating of -1.5. Venus will barely be visible right after sunset very low in the southwest sky. Sirius is two and a half fists above the south-southeast horizon at 6 a.m.

Monday: Did you time the exact length of the day and night last Wednesday on the first day of autumn? They were not equal in duration. Many people think that the day and night are the same duration on the autumnal equinox. The day is a little longer than the night for two reasons. First, the Sun is an extended object so even when the middle part has set, the upper half is still above the horizon lighting the sky. The second, and more influential reason, is that the atmosphere acts like a lens, bending light from the Sun above the horizon when the Sun is really still below the horizon. Day and night are closest in duration today.

Tuesday: Sometimes you find spare change in a chair or an old candy bar in your backpack. Last month, astronomers announced that they found 14 trans-Neptunian objects in old Hubble telescope data. While trans-Neptunian objects will not help you satisfy your hunger, they offer astronomers clues to the origin of the solar system. Pluto is the most well-known trans-Neptunian object. For more information, go to

Wednesday: The International Year of Astronomy (IYA) is winding down. But the size of the objects being featured is not getting any smaller. This month’s Go Observe is the Andromeda Galaxy. On Saturday, I had you look for Triangulum. About one fist above Triangulum is a star twice as bright as the brightest star in Triangulum. From that star, hop about a half a fist up to a star that is about one fourth as bright as the bright star you just found. Less than another half fist in the same direction is a fuzzy oval patch of light called 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. For more information about the Andromeda Galaxy, go to

Thursday: Jupiter is three fists above the southeast horizon at 10 p.m.

Friday: Astronomers, philosophers, and smart children have been contemplating the fate of the universe for centuries. Galileo did not start that trend. But by turning his telescope toward the night sky, he opened a new source of evidence for determining that fate. To honor Galileo’s contribution to this question, the IYA Hot Topic for October is “What is the fate of the universe?”. For more information, go to

The positional information in this column about stars and planets is typically accurate for the entire week.

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