At 3 a.m. Wednesday, local time, we saw Halley's comet winging its way toward Earth outside the orbit of Mars, 124 million miles away. It dominated its portion of the sky, dwarfing every star behind it and standing out like a giant ghostly beacon that is destined to reach the environs of Earth late this year for the 30th time in recorded history since it began appearing in 240 B.C.
We saw Halley's comet through the eye of one of the world's most powerful telescopes, the 60-inch behemoth at the Mt. Palomar Observatory that was built in 1970 and is second at Palomar only to its renowned 200-inch sister telescope, the most powerful astronomical instrument in the world.
"It's extraordinarily bright, much brighter than we expected it would be at this distance," said the Jet Propulsion Laboratories' Dr. James Gibson, the astronomer who ran the Halley show this morning. "As it now stands, that comet's gas and dust cloud measures 90,000 miles across. That means it's grown seven times since I last observed it three months ago."
Gibson paused, then looked questioningly at his guest in a tiny room on the top floor of the darkened dome housing the telescope. Said Gibson: "In a way, I don't believe it. But I guess I have to believe it."
Believe it: Halley's comet is on its way. It may not make the best appearance it's ever made, but it won't be the worst. The comet already has proven to be brighter than expected and has begun to form a broad dust tail that promises to reach epic proportions when the sun's heat and light begin to illuminate the tail just after Christmas.
"We're predicting the tail will grow about 10 to 15 degrees across the sky," Gibson said as we stood mesmerized at what looked like a celestial image of Casper the Ghost. "That's less than half the length of the tail when the comet last appeared in 1910, but you have to remember that in 1910 the comet was so close that the head could be seen in the evening sky at the same time the tail was visible in the morning sky."
The Jet Propulsion Laboratory's Donald K. Yeomans said that astronomers using radio telescopes have measured the equivalent of a ton of ice being boiled off the comet every second that it comes closer to Earth. While this may seem as if Halley's comet is burning itself out, its estimated lifetime is another 200,000 years.
"The rocky core of Halley now appears to be three kilometers across, the size of Manhattan Island," Yeomans said. "If you calculate that it loses roughly one meter of surface each time it circles the sun every 76 years, then theoretically it could make another 260 appearances before it burns itself out."
Looking for Halley's comet through a telescope the size of the 60-inch is like looking right into the heavens from a platform in space. The 60-inch telescope can magnify an object in space the equivalent of 5,000 to 10,000 times. Put another way, it can bring an object in space 5,000 to 10,000 times closer to the eye, making it appear to be within arm's reach.
Gone are the days when astronomers bundled in snow clothes sat freezing in cages with their eyes glued to their telescope. Today's astronomers sit in a heated room adjacent to the telescope, perering at images sent to them by the telescope on a computer screen. The astronomer and a helper called the "night assistant" sit at computer consoles, chatting constantly and tapping out messages to the telescope to tell it where to aim and how long to expose its images.
To an outside observer, the sky looked perfect for viewing Tuesday night. The sun set 60 miles to the east over San Diego in bright, vivid reds that Gibson explained were not good for viewing.
"There are a lot of scattered cirrus clouds in the sky tonight," Gibson complained, "and the moon is about 75 percent illuminated, which means it will scatter even more light through those clouds and make viewing less than fun."
Gibson began his observations as soon as it got dark, but they were not of Halley's comet. First he observed a comet named Holmes, then another named Hartley-Good, then a third named Giclas. Gibson explained why he was saving Halley for last.
"I want the moon to set, so its light will not disturb us," he said. "I also want to wait until Halley is almost directly overhead, which will give us the least possible distortion and the best possible picture."
True to his word, Gibson slewed the telescope in the direction of the constellation Orion, where Halley is now located. He tapped out a message on his computer console, then slammed his index finger on the command button. As if by magic, the television screen alongside the astronomer came to life and Halley burst onto it like an exploding star that was larger than life.
Gibson had found the comet on his first attempt -- not an easy thing from a distance of 124 million miles.