Thursday, January 8, 2009

The Ellensburg Sky for the week of 1/10/09

Saturday: Tonight is the largest full moon of the year. No, the Moon is not actually growing. Although at about 4.5 billion years of age, it could be forgiven a little middle age spread. The Moon’s orbit is elliptical. It gets closer to and farther from the Earth in a predictable pattern throughout the month. When the Moon is closest to the Earth (called perigee) during the full Moon phase, the Moon looks larger and brighter than usual. Tonight, the Moon will look about 14% wider and 30% brighter than the smallest full Moon.

Sunday: Who can forget that memorable song by Three Dog Constellations Night, “The sky is black. The stars are white. Together we learn to find the light.” Well, maybe it didn’t go like that. This is good because not all stars are white. Most stars are too dim to notice a color. But, the stars in the constellation Orion provide a noticeable contrast. Betelgeuse, five fists held upright and at arm’s length above due south at 10:30 p.m. is a red giant. Rigel, the bright star about two fists to the lower right of Betelgeuse, is a blue giant.
By the way, the three dog constellations are Canis Major, the greater dog; Canis Minor, the lesser dog; and Canes Venatici, the hunting dogs. Canis Major contains Sirius, the brightest star in the nighttime sky.

Monday: Mercury is less than half a fist above the west-southwest horizon at 5:30 p.m.

Tuesday: Saturn is about one fist above due east at 10:30 p.m.

Wednesday: This evening, Venus will be as far away from the Sun in the sky as it will get this orbital cycle. Last week, I wrote about the name of this "farthest away" point. Do you remember? Of course you do. It is known as the planet's greatest elongation. Venus is about two and a half fists above the southwest horizon at 5:15 p.m. Over the next two months, Venus will toward the Sun in the evening sky. By late March, it will be lost in the glare of the setting Sun.

Thursday: How do you study the life cycle of a dog? Easy. Get a dog from the animal shelter, care for it for 15 years and study it. How do you study the life cycle of a star? Easy. Pick a star, watch it for a few billion years, and…. Wait a minute. Astronomers can’t observe something for a few billion years. Instead, they study stars that are at different points in their long life cycle and piece together the information from those different stars. What they do is like studying a one-year-old dog for a few minutes, then studying a different two-year-old dog for a few minutes, and so on. The sky in and near the constellation Orion provides an example of four objects at different points of star life.
First, find Rigel, the bright star in the lower right corner of the constellation Orion. It is three and a half fists above due south at 9:30 p.m. About one fist up and to the left are the three objects of Orion’s sword holder. The middle “star” is really a star forming region called the Orion nebula. There you’ll find baby Suns. Now, look about two fists to the right and a little below Rigel. You should be looking at a star that is about one tenth as bright as Rigel but still the brightest in its local region. The third star to the right of that star is Epsilon Eridani, the most Sun-like close and bright star. Betelgeuse, in the upper left corner of Orion, is a star at the end of its life that started out life a bit larger than the Sun.

Friday: Spica, the brightest star in Virgo, is three fists above the south horizon at 6 a.m.

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

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