Jimmy Westlake: Bootes, the celestial cowboy
May 6, 2013
There are 88 constellations in our sky and only one of them begins with the letter B. Know which one it is?
It's Bootes, the Herdsman. This name has been uttered in this form for at least 3,000 years, but at that time, it likely referred to the name of Bootes' brightest star, Arcturus, rather than the whole constellation. Bootes could be the most ancient of our constellations.
Bootes is a celestial cowboy of sorts. Instead of herding cattle, though, this herdsman is rounding up bears. He chases Ursa Major the Great Bear, and Ursa Minor the Little Bear, around the celestial pole once a day. Bootes can be found right on the heels of Ursa Major, whose seven brightest stars also form the Big Dipper.
To locate Bootes, simply follow the curve, or arc, of the Big Dipper's handle around to the big, bright star Arcturus. This dazzling orange star marks the bottom tip of the kite-shaped outline of Bootes, extending to the upper left.
Like Orion, the mythical hunter that dominates our winter sky, Bootes has two canine companions nearby. Their names are Asterion and Chara, and together they form our tiny constellation of Canes Venatici, the Hunting Dogs. Look for the two stars that represent these heavenly hounds directly under the curve of the Big Dipper's handle.
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Arcturus always has been associated with the two celestial bears. The name is derived from the Greek word for bear — "arktos" — and means "bear watcher." I particularly like the Polynesian name for the star, Hokulea, "the star of joy."
Arcturus is much older than our sun, perhaps several billion years older. It already is in the advanced stages of life and has swelled up into an orange giant star 34 times larger than our sun. At a distance of only 37 light years, Arcturus is the brightest star visible in the sky's northern hemisphere and the second brightest star visible overall from Northwest Colorado.
This star's name became a household word back in 1933 when light from Arcturus, focused through a telescope, was used to trigger the opening lights of the 1933 Chicago World's Fair. Astronomers at that time thought the light that arrived from Arcturus in 1933 had started its journey to Earth 40 years earlier at the time of the previous Chicago World's Fair in 1893. Modern measurements have refined that distance downward from 40 light years to 37. Oops.
Jimmy Westlake teaches astronomy and physics at Colorado Mountain College's Alpine Campus. Check out Westlake's astrophotography website at http://www.jwestlake.com.