Wednesday, January 4, 2017

The Ellensburg WA sky for the week of 1/7/17

Saturday: 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. This star, rapidly burning its fuel for a high energy but short-lived existence, is three and a half fists held upright and at arm’s length above due south at 10 p.m. It was not, is not, and never will be like our Sun. However, 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 one fist down from 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.

Sunday: A new year leads us to contemplate our future. Let’s take some time to contemplate the Sun’s future. The Sun has spent a few billion years as a stable star fusing hydrogen into helium. Once that easily fusible hydrogen is gone, the Sun’s outer layer will puff up like a hot air balloon, getting larger, cooler, and redder. The star Aldebaran, in the constellation Taurus looks like what our Sun will look like in a few billion years. Read more about Aldebaran and the Sun’s future at At 9:30 p.m., Aldebaran is almost exactly 60 degrees, or six fists, above due south, about a half a fist to the left of the Moon.

Monday: At 6 p.m., Venus is a little more than two fists above the southwest horizon. Mars is a little more than a fist to the upper left of Mars. The dimmest planet, Neptune, is between the two. Grab a pair of binoculars and orient Venus in the lower right portion of the field of view. Neptune will be in the upper left portion of your field of view.

Tuesday: January is the coldest month of the year so it is time to turn up the furnace. Fornax the furnace is one fist above due south at 7 p.m.

Wednesday: Tonight’s late night full moon is in the constellation Gemini. Tonight’s other Moon is…. Wait a minute. The Earth has only one Moon. True. And it has always had only one Moon. Not necessarily true. According to the best existing model, about four billion years ago, a Mars-sized object collided with the young Earth. The resulting debris coalesced to form the Moon. However, this model left a mystery: why is the Moon so asymmetric? Hardened-lava lowlands dominate the near side while the far side is dominated by mountainous highlands. According to a recent revision of the prevailing model, the early collision formed a large Moon and a small Moon. Over the years, the small Moon caught up to and collided with the large Moon. The highlands are the material from the collided small Moon. For more information about this theory, go to

Thursday: At 6:45 am, Saturn is a little less than one fist above the southeast horizon. Mercury is about one fist to the lower left of Saturn. Jupiter is three and a half fists above the south horizon.

Friday: Have you ever looked down on the ground and spotted a penny? In Yakima? While you were standing in Ellensburg? If you have, then you may be able to see the star Hamal as more than just a point of light. It has an angular diameter that can be directly measured from Earth. Hamal, the brightest star in the constellation Aries the ram, has the same angular diameter as a penny 37 miles away. (For comparison, the moon is about half the diameter of a penny held at arm’s length.) Hamal is three and a half fists above due west at 11 p.m.

The positional information in this column about stars and planets is typically accurate for the entire week. For up to date information about the night sky, go to

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