Comet Hyakutake a Once-In-Many-Lifetimes Event

We're currently completing what aurora researchers refer to as "moon-down time," a two-week period around the new moon when the sky is dark enough to watch the aurora all night.

Although this schedule makes for some groggy mornings for aurora-watching scientists, it also rewarded them with good views of Comet Hyakutake from Poker Flat Research Range. After they finished filming the aurora, the researchers aimed their cameras at Comet Hyakutake, which will perhaps become the brightest comet to pass this close to the earth in 400 years.

"It looks like a fuzzy star," said Geophysical Institute Professor Hans Nielsen.

Early on, the comet was about as bright as the faintest star in the Big Dipper, but it brightened as the comet continued its egg-shaped orbit around the sun. Alaskan sky-watchers were able to see the comet without even using binoculars as it appeared to pass by the Big Dipper.

Yuji Hyakutake, of Japan, discovered the comet on January 30 while scanning the sky with 25 x 150 binoculars. Although Hyakutake's was the first recorded sighting, Nielsen said the comet probably passed by the earth some 10,000 to 20,000 years ago.

Unlike Halley's Comet, which orbits within earthlings' view about every 75 years, Comet Hyakutake is one of many long-period comets, the great wanderers of our solar system. Long-period comets take at least 200 years to orbit the sun.

Comet Hyakutake comes from a large pool of comets milling about at the edge of the solar system. In 1950, Dutch astronomer Jan Oort suggested the existence of a vast reservoir of comets swirling beyond Pluto, the farthest planet from the sun; Within this spherical "Oort Cloud," stars passing close to comets can disrupt their orbit. These stars have the effect of slinging comets into the inner solar system, close enough to the sun for its gravity to capture them.

Comets such as Comet Hyakutake become visible when they reflect the light of the sun. The sun also makes comets easier to see by heating them up so much that they trail a cloud of gases. In fact, the word "comet" is derived from the Creek word "kometes," (hairy) which refers to a comet's tail of plasma and dust.

Nielsen describes comets as "dirty snowballs," composed of frozen water, ammonia, methane, carbon dioxide and other compounds embedded with dust and rock.

With each pass near the sun, a comet loses size until it disintegrates, a process that---while it may make take hundreds of thousands of years---is inevitable.

"Comets are doomed once they get into the inner solar system," Nielsen said.

Comet Hyakutake, 40 times larger than the earth, passed within 9.3 million miles of the earth on March 25. That may seem pretty distant, but the sun is 10 times farther away.

If you missed Comet Hyakutake, another recently discovered comet (Hale-Bopp) should pass near the earth next winter. Alaska will again be an ideal place to view the comet because the constellations it will pass through are all above the horizon for 24 hours in Alaska.

Because unexpected comets can appear as suddenly as Hyakutake and Hale-Bopp both did, any amateur astronomer has a chance of having his or her name attached to a dirty snowball floating around the heavens for thousands of years. All it takes is darkness, clear skies, and patience. Better grab your coat and binoculars.