On early summer evenings, one of the first bright lights to blink through the gathering darkness is Arcturus, which lies almost directly overhead as night falls.

Arcturus, truly a star among stars, was singled out for mention in the Bible, where God drops its name in conversation with Job. Arcturus also appears in the writings of Homer, Hippocrates and those of the great English poets Lord Byron and Alexander Pope. Illuminating science, Arcturus in 1635 became the first star ever seen through a telescope in the daytime. A century later Arcturus gave astronomers their first hard lessons about the vastness and strangeness of deep space. And by virtue of its brilliant proximity, Arcturus was pressed into service for the bang-up opening of the 1933 "Century of Progress" exposition in Chicago, when the star's light actually tripped the switch for the flood lights at the fairgrounds.

If you see something worth wishing upon, high in the July night, you've probably found Arcturus already. Observers rank it as the brightest star in the northern sky. (Ignore what Jiminy Cricket and various popular songs say about the North Star, also called Polaris or the pole star. Arcturus outshines it by far, ranking fourth among all stars, while Polaris trails way behind at position 49.)

If you look skyward well after dark, when the night is crowded with stars, the Big Dipper will direct you to Arcturus. Start from the Dipper's four-star bowl and proceed dot-to-dot along the three stars that draw the Dipper's curved handle. Then let your eyes continue the arc begun by the handle. Stop at the first bright star you encounter.

Arcturus has a distinctly orange tinge compared to its neighbors. The color coordinates with the star's current condition as a "red giant." In other words it has burned through its stores of the simplest element, hydrogen, which is a star's primary fuel. Now Arcturus shines by fusing together atoms of helium. Puffed up by this process, Arcturus has expanded to a diameter some 25 times that of our sun, though it is only a tiny fraction as dense. Were the two stars viewed side by side,

Arcturus would appear more than one hundred times more luminous.

Arcturus seems to mark the bottom point of a big star picture of a child's kite, which is its home constellation, Boötes (the Herdsman). The brightest star in Boötes, Arcturus attracts as much attention as all the lesser lights combined. In the several millennia of mythology surrounding this group, Arcturus alone has often stood for the entire constellation.

Arcturus takes its name from its nearness to the sky bears, Big and Little, otherwise known as Ursa Major (the constellation containing the Big Dipper) and Ursa Minor. "Arcturus" in Greek means "bear watcher" or "guardian of the bears."

Early stargazers had charted Arcturus' position, and those of other bright stars, on their first maps of the heavens. Centuries later, when famed British astronomer Edmond Halley reviewed these maps in 1718, he noticed that Arcturus was way off course. Giving his forebears the benefit of the doubt in fixing the star's correct position in ancient times, Halley entertained the idea that Arcturus and other "fixed" stars might actually travel through space. This was a radical idea for his day, when most people believed that only the planets moved against the background of the immutable stars.

Halley called the phenomenon of star wandering "proper motion." Arcturus displays a remarkably high proper motion of about 90 miles per second. Rushing through the complex geometry of space, Arcturus approaches the sun at three miles per second. But even this rapid rate escapes our casual notice because of Arcturus' great distance from Earth (measured in hundreds of trillions of miles). Therefore you can comfortably expect to find it every night in the same sky site for centuries to come. As it continues cutting through the star fields of the Milky Way, however, Arcturus will pass our solar system and recede so far from this vicinity that it will fade from naked-eye view in about half a million years.

Meanwhile Arcturus lies 34 light years away, which means that if you look up at this star tonight you will see light that left it 34 years ago.
Dava Sobel watches her patch of the night sky just above Long Island, N.Y., without the aid of anything so newfangled as a telescope. Send her your questions and observations at

stargazer@discovery.com.