Celestial News: Follow the Arc to Arcturus
There are 88 constellations in our sky, and only one of them begins with the letter B. It’s Bootes, the Herdsman (pronounced bow-oh-teez), and it could be the most ancient of our constellations.
The name of Bootes has been spoken in this form for at least 3,000 years, as it first appears in Homer’s Odyssey. At that time, however, it most likely referred to the name of Bootes’ brightest star, Arcturus, rather than the whole constellation.
In Greek mythology, Bootes was considered a shepherd or a herdsman, chasing the Big and Little Bears around the pole of the sky with his two leashed pooches, Asterion and Chara. These two hunting dogs are found in their own small constellation nearby, Canes Venatici.
Bootes is often identified with the Greek hunter Arcas, the son of Zeus and a mortal woman named Callisto. When Zeus’ jealous wife, Hera, found out about the love child, she changed Callisto into a bear, destined to roam the forest forever.
When Arcas grew up, he was out in the forest one day and saw a huge bear running toward him. He prepared to fire an arrow to kill the bear, not realizing that it was his own mother who had recognized him from afar.
Zeus intervened just in time, changed Arcas into a little bear, grabbed both bears by their short, stubby tails, slung them round and round and slung them up into the heavens where they were transformed into the stars of our constellations Ursa Major and Ursa Minor, the Big and Little Bears. This unusual launching technique explains how the celestial bears’ tails became so long.
Locating Bootes and its bright star Arcturus is a snap. Just face the northeastern sky after 8:30 p.m. in early April and use the handle of the Big Dipper as a pointer — follow the arc of the curved handle, and it will lead you right to Arcturus. The stars of the constellation Bootes form the outline of a kite-shaped figure, with Arcturus marking the bottom point of the kite.
Arcturus is the brightest star visible in the sky’s northern hemisphere and the second brightest star visible overall from Northwest Colorado. Only the Dog Star, Sirius, appears brighter in our sky. This prominent orange star is already in the advanced stages of life and has swelled up into an orange giant, 34 times bigger than our Sun.
The name Arcturus is derived from the Greek word for bear, arktos. Literally, the name Arcturus translates into “the Bear Watcher” or “Bear Chaser.” Bootes is a cowboy, of sorts, chasing the two bears around the pole of the sky in a celestial bear round up.
The star Arcturus became world famous when its light was focused through a telescope and used to switch on the lights of the 1933 World’s Fair in Chicago. This particular star was chosen because the starlight that arrived in 1933 was thought to have left Arcturus 40 years earlier during the previous Chicago World’s Fair in 1893. Modern measurements, however, place the star’s distance at 37 light years instead of 40.
Jimmy Westlake retired from teaching at Colorado Mountain College Steamboat Springs in 2017, after 19 years as professor of physical sciences. “Celestial News” appears monthly in Steamboat Pilot & Today. Check out Westlake’s astrophotography website at jwestlake.com.
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