The most spectacular comet in two decades, already visible to the naked eye, will grow brighter and closer over the next few days as it zips past the Earth.
Named after the amateur Japanese sky-watcher who discovered it just a month and a half ago, Comet Hyakutake will come closest to Earth on Monday and remain part of the night sky throughout April. Though it will dim somewhat after next week, Hyakutake may become an even more impressive sight from Earth as it moves toward the sun if it develops the long, tail that people associate with these celestial travelers.
Astronomers around the world are hurriedly preparing for the comet's fly-by--at its nearest point, it will be a mere 9.5 million miles away. This will be comet researchers' first chance to take full advantage of a gaggle of sophisticated instruments--including the Hubble Space Telescope and arrays of radio telescopes--that have been developed since Halley's Comet swung by in 1986.
Their observations could help untangle the many mysteries that still cloud comets, including exactly what makes up the "dirty ice balls" and whether pebble-size pieces are crumbling off in addition to the jets of dust and gas.
Tonight, Hyakutake will rise at about 8 p.m. over the eastern horizon, a faint, fuzzy ball several times larger than the moon--"looking maybe a lot like a cloud," according to Brian Marsden of the Harvard Smithsonian Center for Astrophysics in Cambridge.
The best time to see it will be a couple of hours later when the comet clears the low-level haze, said John Mosley, an astronomer at the Griffith Observatory. To avoid the city lights and smog, Mosley recommends heading to the mountains. Binoculars will aid in picking out the comet, he said.
"Face east and look up around 11 p.m. about a third of the way up the sky," Mosley said. Currently, Mosley said, the comet can be found next to Arcturus, a bright star that can be located by following the handle of the Big Dipper.
In the coming days, as the comet travels closer to the sun, its position in the sky will shift northward, and it will appear earlier and earlier. Beginning Sunday, the comet will be visible from sundown to nearly sunup.
A binge of comet activities at Griffith Observatory include comet observing sessions beginning Friday night, a special planetarium show and a lecture next Monday.
The observatory also has a comet hotline at (213) 663-8171, though the phone lines have been jammed, Mosley said.
Comets are balls of ice, frozen gases and dirt, typically a few miles across. Scientists believe a giant ring of comets orbits the solar system at a distance about 1,000 times farther from the sun than Pluto. The occasional gravitational rumbling of a passing star dislodges some of the comets, sending them on a highly elliptical path toward the inner solar system.
Astronomers estimate that Hyakutake last flew by Earth 15,000 to 20,000 years ago.
Hyakutake's surface has already started heating up on its journey toward the sun, releasing some of the gases to form a surrounding cloud about 50,000 miles wide.
In a typical year, two or three comets wander within the Earth's orbit, but none in recent years has been particularly bright or close to Earth, making observation difficult.
"It just ends up pretty frustrating in cometary science," said Patrick Palmer, a University of Chicago astrophysicist. "It's rare that we get a really good comet like this."
Astronomers, who had been preparing for a comet called Hale-Bopp that will pass by Earth next year, were caught off guard when Hyakutake appeared.
"Everyone was gearing up for Hale-Bopp," said David Schleicher, an astronomer at the Lowell Observatory in Flagstaff, Ariz. "Now it's like, 'Oh, gee, let's panic.' "
Because Hyakutake passes so close to Earth, Schleicher and his colleagues hope to snap photographs of the central core, usually obscured by the glow of escaping gases. That would allow a more precise estimate of the comet's size, which astronomers guess is between five and 10 miles wide.
Other astronomers, such as Palmer, will be using a system of radio telescopes near Socorro, N.M., to measure the echoes of radar signals bounced off the comet. Scientists hope to detect the telltale signs of various molecules that they suspect exist in the comet.
Of the 100 or so types of molecules known to inhabit the interstellar regions, so far only about 30 have been detected in comets. "We think there should be others," Palmer said.
Scientists believe that comets colliding with Earth provided many of the ingredients necessary for life. They hope that molecular information from Hyakutake and other comets will give them insight into the origins of life.
The Hubble Space Telescope will similarly search for evidence of other molecules by scanning emissions in the ultraviolet range--radiation that ground-based observers cannot detect because it gets filtered out by the atmosphere. The space telescope also promises some spectacular photographs.