Friday, August 28, 2009

The Ellensburg Sky for the week of 8/29/09

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 above the south horizon.

Sunday: Venus is two fists above the east horizon at 5:30 a.m. Mars is four and a half fists above the east-southeast horizon at this time. Nearly 400 years ago, Galileo discovered that Venus goes through phases from new to quarter to full just like our moon does. Thanks to this and Galileo’s many other observations of moons and planets in our solar system, support for an Earth-centered universe was greatly diminished. To commemorate these findings, NASA has made planets and moons this month’s “Hot Topic” for the International Year of Astronomy. For more information, go to and click on September.

Monday: The bright star Capella is just above the north horizon at 8:30 p.m.

Tuesday: “I’m a little teapot, short and stout. The galactic center, I pour it out.” (I’m a Little Teapot, astronomy version, 2009.) 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 if 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 see the actual galactic center, you can gaze in the direction of the center by looking 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: Jupiter is about a half a fist to the lower right of the Moon at 8:30 p.m. Galileo’s discovery of the moons of Jupiter provided strong evidence that objects other than the Earth could have satellites providing more support for a Sun-centered solar system. For more information about Jupiter or observing Jupiter, go to and click on September.

Thursday: It is a good thing Galileo didn’t turn his telescope toward Jupiter tonight from 9:40-11:30 p.m. He would not have seen any moons, people would still think the Earth was at the center of the universe, science would have ground to a halt, and historically important inventions such as music videos and electric can openers would have never been created. “Poppycock”, you say? Evaluate your own feelings tonight. From 9:40 to 11:30 p.m., the four largest moons of Jupiter, Io, Europa, Ganymede, and Callisto will either be in front of or behind Jupiter meaning they can’t be seen from Earth with a small telescope. Jupiter will appear moonless from Earth for over 100 minutes. For more information, go to

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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