This is what the Oort cloud might look like. Courtesy of NASA Jet Propulsion Lab.
Astronomers think there may be as many as one trillion comets whirling around our solar system.
So why don't I see them more often?
And what's the big deal when one sweeps past Earth?
Most of these comets, explains Jay M. Pasachoff, an astronomer at Williams College and author of Astronomy: From the Earth to the Universe, are trapped at the very margins of our solar system in a huge sphere beyond Pluto known as the "Oort Comet Cloud." This cloud, named after, Dutch astronomer Jan H. Oort, who first proposed it, surrounds our solar system. An occasional gravitational tug or push from a nearby star can kick a comet loose and send it off into space -- or into a long elliptical (defined) orbit around our sun.
(Comets move extremely slowly in the Oort Cloud. But they are not hanging around motionless, like teenagers at the corner drugstore. Why? Because they obey Johannes Kepler's second law of motion, which dictates that objects in elliptical orbits will move very slowly when far from the sun, and very fast when near it.)
Because comets seem to "live" in a huge cloud at the edge of our solar system, they are highly unpredictable, since they can come at us from any direction -- at any time.
Many comets are discovered by amateur astronomers like Yuji Hyakutake, the Japanese man with giant binoculars who spied the comet that bears his name that's now overhead.
They are usually detected as they make their way into the inner solar system and skim past the Earth. Comet Hyakutake is exciting because it will pass relatively close to our planet, a measly 15 million kilometers (9 million miles) away.
Astronomers have discovered about 1,000 comets so far, but most are so dim that noboby else knows about them. About a dozen new ones are spotted each year.
How can I see this speeding bullet?
It's the biggest furry blob in the north sky. That's right -- the one with the tail. Find the darkest place you can for viewing.
Okay, so a comet looks pretty cool but what does it all mean?
