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Astronomy ... and You, 2020
“Uncle Bob”

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Boötes … and You

Author Sidney Hall (1825). Restoration by Adam Cuerden

Boötes, the Herdsman …

I have a favorite star. It is the alpha star in constellation Boötes. It is also known as Arcturus, seen above at the Herdsman's left knee. It strikes me as champagne colored, and that impression rings my chimes. I’ve been to more than one frosty get-together that has reaped the rewards of a champagne ice-breaker. Arcturus is the fourth brightest star in our sky.

Fourth brightest even though its color is not a blazing hot blue or white. I see it as a mature yellow, and some have reported orange-yellow. It is spectrally classified a K-star, and so visual reports are in the range. The infrared energy we receive from Arcturus is even measurable at one candle 5 miles away. Can you feel the burn?

Arcturus has a proper motion that makes it unique. Even at the short span of 25 years, photographic plates make its change in position obvious. If we apes were looking up a half-million years ago, we would have seen a new star appear – that's when Arcturus became visible. It is presently at its closest approach, 37 light-years distant, but in another half-million years, it will pass our purview and disappear once again.

How do you say Boötes? Even the question has too many o’s in it. Soooh, experts tell me it’s Boh-OH-teez. What? A herder, a tease?

In myth, Boötes –go ahead, practice it a bit – is known as the herdsman, and has been assigned two important jobs. [See Uncle Bob last month for the Ursa Major article.] Boötes must keep guard on the Great and Little Bears as they trudge relentlessly around the North Star Polaris every day. Boötes was honored with a place in the sky for being the inventor of the ox-drawn plow. He is in perfect position to wield the Big Dipper which is sometimes referred to as The Plow.

Finding Arcturus - drawn by Jim Thomas in 2006.
free image under GNU General Public License

You can use the Dipper to locate Boötes and its alpha star. Follow the curve in the Dipper’s handle and continue “arcing toward Arcturus.” The lovely warm star is at the base of what looks to me like a tall skinny kite. A short tail trails west of Arcturus. Proceeding northward you’ll find a pair of stars delineating a slender waist. The constellation then opens wider to a crown of three stars at the top.

Author: Sanu N. Licensed under the Creative Commons Attribution-Share Alike 4.0

Boötes boasts two significant double stars. One is epsilon, the star to the left at the waist of the kite, and the other east of Arcturus. Epsilon, known as Izar is a fairly wide double with a color contrast, but it requires a small scope to separate its components. Xi Boötes, at 22 light years is relatively close, but the pair are also very close at 3 seconds of arc from our perspective.

... and You


1. Proper motion. Compare Arcturus’s present distance of 37 light years to the distance it traveled over the half-million years since it became visible to us (or our prehistoric ancestors, that is).


2. Izar. Some binary stars whiz around one another at a dizzying pace, while others seem content to take a thousand or so years for a complete revolution. The way we keep track is by making observations of the system’s separation and the position angle of the secondary star. Even amateur observers can do this and contribute to the science. Look into these measures, and see how they apply to the wide double star Izar.




3. Coma Berenice, or Bernice’s Hair can be seen at lower right in our lead illustration above. The myth of how this set of locks were placed in the sky is a tale for the ages. The group of stars themselves are a measure of how good your spring night sky is for viewing. They are a faint sprinkle which almost anyone can fantasize as the golden tresses of an historic beauty. Check for a right angle of stars between Arcturus and Leo, and suspended below the westerrnmost star will be the comely tresses.


Sources: Burnham’s Celestial Handbook, Audubon Field Guide

Next Month: The Mighty Hercules

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