The North Star: A Moving Target

One of my earliest memories of looking up at the night sky happened when I was about 6 or 7 years old. I was visiting an uncle of mine, and on an early fall evening at dusk he pointed almost directly over our heads at a brilliant, bluish-white star. "See that star, Joey? That's the North Star, the brightest star in the sky."

Of course, my uncle was dead wrong on two counts.

First, the North Star is not the brightest star in the sky (although that's indeed a popular misconception). Polaris, the actual North Star, ranks only 49th in brightness.

Second, the North Star would appear directly overhead from only one place on the Earth, namely the North Pole.

In fact, the bright star at which my uncle was pointing, which appears almost directly overhead as darkness falls on late-September evenings, is Vega, in the constellation of Lyra, the Harp. It's not the brightest, but actually the fifth brightest star in the entire sky and the third brightest visible from midnorthern latitudes (like Chicago and New York), behind Sirius and Arcturus.

Also, as seen from midnorthern latitudes, Vega goes below the horizon for only about seven hours a day, meaning that you can see it on any night of the year. Farther south, Vega is below the horizon for a longer interval of time. Conversely, for Alaska, central and northern Canada, as well as central and northern Europe, Vega never sets, and is readily visible on any clear night.

Vega is the brightest of the three stars forming the large "Summer Triangle," the other two stars being Altair and Deneb. Vega is located 25 light years away, has a diameter approximately three times that of our Sun and is 58 times more luminous.

A solar system in the making?

In January 2002, astronomers at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. announced that features observed in a cloud of dust swirling around Vega may, in fact, be the signatures of an unseen planet in an eccentric orbit around the star.

Observations of Vega in 1983 with the Infrared Astronomy Satellite provided the first evidence for large dust particles around another star, probably debris related to the formation of planets. This discovery likely inspired the late astronomer Carl Sagan to place a planet orbiting Vega in his novel, "Contact."

"Say cheese"

Vega also holds a rather unique place in the annals of astronomy as being the first star ever to be photographed. The historic photograph was made using the daguerreotype process at Harvard Observatory on the night of July 16-17, 1850. A 15-inch refractor was used, and it still took an exposure of 100 seconds for Vega's image to register.

Lyra was supposed to represent Apollo's harp. Officially, Lyra is a lyre — a stringed instrument of the harp family used to accompany a singer or reader of poetry, especially in ancient Greece. Six stars form a combined geometric pattern of a parallelogram and an equal-sided triangle attached at its northern corner. Vega gleams at the western point of the triangle.

North Star of the future

A final note: Because the Earth's axis very slowly oscillates like that of a spinning top (in a movement called precession), the North Pole traces a circle on the sky, pointing to different stars as it moves along in a circuit that takes about 26,000 years. And 12,000 years from now, the Earth's axis will pointed in the general direction of Vega, which will then be the North Star.

I'm sure that will make my uncle very happy.