Thursday, August 25, 2011

The Ellensburg sky for the week of 8/27/11

Saturday: School starts next week so it is time for a little geometry review. Go outside at 10 p.m. tonight with notebook in hand. Ready? A triangle is a polygon with three corners and three line segments as sides. A good example is the Summer Triangle made up of the bright stars Vega, Deneb and Altair. Vega, the brightest star in the triangle is a little bit west of straight overhead. Deneb is a little bit east of straight overhead and Altair is five fists held upright and at arm’s length above the south horizon.

Sunday: Jupiter is one fist above the east horizon at 11 p.m.

Monday: WISE finds some Y’s and they’re as cool as your eyes. NASA’s Wide-field Infrared Survey Explorer, WISE for short, has discovered a type of brown dwarf that astronomers are calling a Y dwarf star. Astronomers study brown to better understand how stars form and to understand the atmospheres of gas giant planets like Jupiter. These Y dwarf stars are on the classification boundary between stars that fuse hydrogen at their core, like our Sun does, and objects similar to Jupiter and other newly discovered planets that are a little too small to be a star. One of these Y dwarf stars is only nine light years away making it the seventh closest star system. For more information about this discovery, go to

Tuesday: “I’m a little teapot, short and stout. The galactic center, I pour it out.” (I’m a Little Teapot, astronomy version, 2011.) Despite its great size and importance, the center of our Milky Way galaxy and its giant black hole remains hidden to the naked eye behind thick clouds of gas and dust. By plotting the orbits of stars near the middle of the galaxy, astronomers have determined that the black hole’s mass is equal to about 4.5 million Suns. While you can’t see the actual galactic center, you can gaze in the direction of the center by looking just to the right of the teapot asterism in the constellation Sagittarius. This point is about one fist above the south-southwest horizon at 9 p.m.

Wednesday: Ah, the beauty of classification. A large three-sided figure such as the Summer Triangle is a triangle. Hence the name “Summer Triangle” and not “Summer Sandwich”. Although those little triangle-shaped sandwiches are quite tasty. Where was I? Oh yes, classification. Any three-sided figure is called a triangle. Just after sunset, Saturn, the Moon, and the bright star Spica make a small right triangle very low in the west-southwest sky. Spica is a half a fist to the upper left and Saturn is a fist to the upper right of the Moon.

Thursday: The morning sky is filled with visible planets. At 5:30 a.m., Mercury is a half a fist above the east-northeast horizon, Mars is three and a half fists above the east horizon, and Jupiter is five and a half fists above the south horizon.

Friday: The Ellensburg Rodeo is a “Top-25” rodeo. What does it take to be a “Top-25” star? There are many ways to rank stars. The most obvious way for a casual observer to rank stars is by apparent brightness. The apparent brightness is the brightness of a star as seen from Earth, regardless of its distance from the Earth. Shaula (pronounced Show’-la) is the 25th brightest star in the nighttime sky as seen from Earth. It represents the stinger of Scorpius the scorpion. In fact, Shaula means stinger in Arabic. Shaula has a visual brightness rating of 1.62. Sirius, the brightest star has a visual brightness rating of -1.46. (Smaller numbers mean brighter objects.) The dimmest objects that can be seen with the naked eye have a visual brightness rating of about 6. There are approximately 6,000 stars with a lower visual brightness rating than 6 meaning there are 6,000 stars visible to the naked eye. Shaula is a blue sub-giant star that radiates 35,000 times more energy than the Sun. It is 700 light years away making it one of the most distant bright stars. Shaula is a challenge to find because it never gets more than a half a fist above the horizon. Look for it tonight about a half a fist above the south horizon, a little bit west of due south, at 8:30.

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

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