Comet C/1999 S4 Linear, which is currently traveling near the Big Dipper toward the western horizon, will attain its maximum brightest about July 23 at roughly 6th magnitude. The comet will come within 71 million miles of the sun on July 25.

Warmed by the sun, the comet's tail has attained the angular length of two full moons. Unfortunately, the comet will not live up to early, optimistic estimates of a maximum brightness of 3rd magnitude.

(In 1997, Hale-Bopp, the most recent naked-eye comet, reached a stunning -2 magnitude.)

Comet Linear will be visible with binoculars and telescopes only through the first week of August from the Northern Hemisphere, after which it will dip below the horizon and disappear.

"The best show will be during the last two weeks of July when it should be visible with the naked eye from a dark location," said Richard Talcott, associate editor of Astronomy Magazine.

Astronomy Magazine is hosting a star party to help the public view the comet from one of the darkest spots in the continental United States - Yellowstone National Park in Wyoming. The Rocky Mountain High Star Party will be held near Yellowstone's Madison amphitheater the evenings of July 21 and 22 and at the Chittendon parking area north of Mt. Washburn on July 22.

"Comets bright enough to see with the naked eye occur roughly every three to five years, and dozens of comet enthusiasts from across the United States are planning to watch this one with us," said Astronomy senior editor Rex Graham.

The free star parties are co-sponsored by the park, the Museum of the Rockies in Bozeman, Montana, and amateur astronomers from Montana. Astronomy editors Graham and Talcott also will present a series of daytime talks on comets at Old Faithful Visitor Center on July 21 and 22 and at Albright Visitor Center at Mammoth Hot Springs on July 22.

Linear is an acronym for Lincoln Laboratory Near-Earth Asteroid Research, the discovery project. The Linear team used a state-of-the-art 39-inch robotic telescope to find the comet as well as hundreds of other asteroids and comets as faint as 19th magnitude. C/1999 S4 Linear came from the distant Oort Cloud of comets in the outer reaches of the solar system.

Volatile surface ices such as carbon dioxide vaporize and fuel the brightness of such first-time comets. However, more than one trip around the sun is usually needed to liberate enough cometary-dust particles and water vapor so that a comet can reach its full potential to shine.

Unfortunately, Comet Linear will disappear from earthly views in August when it glides closer to the sun's glare and then travels around it and speeds off to the far reaches of the solar system. Linear's next trip through the inner solar system will be in about 30,000 years.

Astronomy Magazine

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