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Bright Arcturus, High in Our Sky, Shepherds the Great Bear Around the Pole

+ Von Del Chamberlain +

I hope readers of this column have noticed the bright star now high in the south as darkness comes. It is the fourth brightest in the night: second brightest we can see from our latitude. The star is Arcturus, in the constellation Boötes (pronounced Boh-oh-tease), the Herdsman. The name Boötes comes from a Greek word meaning "noisy," referring to a herder shouting at his animals. In this case, the animal is none other than Ursa Major, Great Bear of the north.

Arcturus is easy to find. It is high in the sky, just southwest of overhead, as darkness comes in early July. To be sure you have found it, locate the Big Dipper in Ursa Major, high in the northwest at eventide, then follow the arc of the dipper handle and it will lead you to Arcturus:

"Follow the arc to Arcturus," is the common statement used by many to remember the star and its location. Boötes is usually visualized as a human figure, but is easier to see as a kite, or even as an ice cream cone, with Arcturus at the end of the kite-tail or bottom of the cone. The scoop of ice cream is very nearly straight up, higher than Arcturus, as it gets dark. As the night continues, these stars progress down toward the west.

Arcturus sparkles like a golden-yellow topaz on clear spring and summer evenings. It was one of the first stars named and has been referred to frequently in literature both old and new. Being near Ursa Major, the Great Bear of heaven, it has been called the "Watcher," or the "Guardian." In Homer's Odyssey Boötes is referred to as "The Bear Driver," but the Arabs referred to Arcturus as "Lance Bearer" and "Keeper of Heaven," and it has also been called "Job's Star," since it is mentioned in the book of Job, chapter 38, verse 32: "Canst thou bring forth Mazzaroth in his season? or canst thou guide Arcturus with his sons?" This is now thought to be a bad translation: the original text probably referred to the Great Bear constellation rather than to the star Arcturus.

In Greek mythology Boötes, son of Demeter, goddess of agriculture, invented the plough in order to support himself by tilling the soil. He was placed in the sky, near Ursa Major, sometimes viewed as a plough, in honor of his service to mankind. For the Greeks, Ursa Major was the Great Bear of Heaven, but in China it was visualized as a wagon, in England it is a plough, for some Arabs animals in a field, and in parts of Native America hunters chasing various animals. The star Arcturus is always associated with Ursa Major, following along behind the Dipper, the Wagon, the Bear or other animals at a safe distance as if driving, herding, guarding, tending or hunting. Thus the constellation Boötes and its bright star Arcturus are shepherd of Arabian pastures in the sky, cosmic wagon master of ancient China, ploughman of celestial fields, and both guardsman and hunter of the Great Bear of Heaven. They are constant in their vigil over the most prominent stars that circle round the celestial pole.

Bright Arcturus is currently a neighbor to the Sun, only about 36 light years away, close for a star. However, it belongs to an entirely different set of stars making up the Milky Way Galaxy. Whereas the Sun moves within the plane of the Galaxy, Arcturus is part of a great spherical galactic halo, moving in an elliptical orbit. Currently it is coasting near us through the galactic plane, drawing 3 miles closer to us each second as it moves 90 miles each second through space in the direction of the constellation Virgo. It's rate of motion relative to us will diminish over the next several thousand years, then it will recede until no longer visible to the naked eye in another 500,000 years.

Arcturus is cooler, but 115 times brighter, than the Sun. It's diameter is about 25 times that of the Sun and it has about 4 times the solar mass.

In 1933 Arcturus came to national attention when its light was used to activate searchlights at the "Century of Progress" Exposition in Chicago. The star was used to officially open the Exposition because it was then estimated to be located 40 light years away. A previous fair had been held in Chicago in 1893. Thus, the light that had left Arcturus in about 1893 was used to ignite a fair again in Chicago 40 years later.

Another interesting fact about Arcturus is that it was the first star (other than the Sun) on record to be observed during daytime. It was observed in daylight with a telescope in 1635, a feat easily duplicated today with a good amateur telescope.

It is so pleasant to go out and look around on warm summer evenings. When you do, find the Great Dipper in the Great Bear Ursa Major. "Follow the arc to Arcturus," the Bear Driver" in the constellation Boötes, the Herdsman. Enjoy this jewel of heaven, perhaps contemplating the many others through human history who have stood, like you, gazing at this bright star. Continue following the arc from the handle of the Dipper past Arcturus and downward toward the southwest to find the bright white star Spica in the constellation Virgo. Now that you are looking toward where Arcturus is headed in space, consider the future and what it might bring to humankind as Arcturus moves past us to eventually recede in the distance. What will the astronomical moments when Arcturus gleamed brightly in our sky have accomplished for people residing on the third planet out from the Sun?

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