Thursday, January 15, 2009

The Ellensburg sky for the week of 1/17/09

Saturday: Astronomers have just solved a mystery about the fifth brightest star in the nighttime sky, Vega. For decades, astronomers have known that Vega is about 50% brighter than it should be, given its temperature. That gave scientists two choices: either revise their temperature-brightness model or look for a characteristic they have overlooked when applying the model. Some people say if an observation goes against a scientific model, the model is bad and should be thrown out. But, that is not how science works. Models in science are built using many observations. It does not make sense to abandon a model when one observation seems to refute it. So, scientists looked for a reason Vega is brighter than expected. They finally found one. Using a powerful array of telescopes, astronomers noted that Vega is oblong, due to rapid rotation, and we are observing the star nearly pole-on. Thus, we are observing the widest possible diameter for Vega. The light from this oblong star is spread out more than the light from a round star. Spread out light means the star appears brighter. Look for brighter than expected Vega one fist held upright and at arm’s length above the northeast horizon at 7 p.m.

Sunday: This morning’s last quarter moon is in the constellation Virgo. Virgo, the second largest constellation in the sky, after Hydra, is typically identified with Dike, the goddess of justice. A stature of justice at a courthouse is really a statue of Virgo.

Monday: Sirius, the brightest star in the nighttime sky, is two and a half fists help upright and at arm’s length above the south horizon at 10 p.m. Some stars, such as Antares and Betelgeuse, appear to us to be bright because they are luminous supergiant stars. Sirius appears bright to us because it is just down the block in our galactic neighborhood. In fact, if you shrunk the Milky Way galaxy down to the size of Ellensburg, Sirius would be about one foot away from your nose.

Tuesday: Venus is nearly three fists above the southwest horizon at 6 p.m.

Wednesday: The brightest star in Scorpius is Antares which means “rival of Mars”. But, this morning, Antares is a rival of the moon. So the moon, like most things when faced with a rival, will attempt to overpower Antares by blocking, or occulting, it. From Ellensburg, the moon will appear to pass less than a finger’s width below Antares. At 6:30 a.m., they will be one fist above the south-southeast horizon. The complete occultation will be visible from central South America.

Thursday: Saturn is one fist above the east horizon at 10 p.m.

Friday: Did you see Saturn last night? You may have confused it with Regulus, the brightest star in the constellation Leo the lion. Regulus is three fists above the east-southeast horizon at 10 p.m., about two fists to the upper right of Saturn.

The positional information in this column about stars and any planet except Mercury is accurate for the entire week.

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