Friday, January 5, 2018

The Ellensburg WA sky for the week of 1/6/18

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: Jupiter and Mars are neighbors in the morning sky all this week. Look two and a half fists above the south-southeast horizon at 7 a.m. Jupiter, the brighter planet, is about the diameter of the full Moon above Mars. For an added challenge, look for Mercury and Saturn low on the southeast horizon. Mercury is a half a fist above the horizon and Saturn is about a thumb width above the horizon at 7 a.m. As the week goes on, these two planets will move closer together in the sky.

Monday: 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. Hear 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.

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: 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.

Thursday: This morning, the Moon joins Jupiter and Mars in the south-southeastern sky. The two planets are less than a half a fist to the lower right of the Moon at 7 a.m.

Friday: Mercury and Saturn are side by side in the morning sky; about a half a fist above the southeast horizon at 7 a.m. Mercury is the brighter of the two planets and is on the right.

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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