Yes, that was the sky falling over the San Francisco Bay area Wednesday night, and yes, there will be more of it this weekend. But, no, astronomers say, it is not something to worry about -- more likely, if you're so inclined, a sight to be savored.
Hundreds of people from San Francisco, Oakland and Santa Cruz called ABC station KGO-TV, reporting a loud boom and streaks of light in the sky around 7:45 p.m. local time Wednesday. Astronomers cannot be sure about any one report, but they suspect it was an errant piece of rock from the asteroid belt between Mars and Jupiter, traveling in an orbit that happened to send it tearing into the atmosphere over California.
"Basically, you saw small car-sized pieces of rock and metal from the asteroid belt, crashing through layers of earth's atmosphere, ionizing and setting the air on fire in its wake," Jonathan Braidman, an astronomer at the Chabot Space and Science Center in Oakland, told KGO.
Bill Cooke of NASA's Meteoroid Environment Office said the object was traveling from the southeast to the northwest. "If any of it survived as meteorites [pieces reaching the ground]," he said, "you're going to need scuba gear to collect them, because they probably crashed into the Pacific."
The fireball lit up the Web today, partly because it passed over a populated area, and partly because it coincides with the Orionid meteor shower, which peaks Saturday night -- best seen in the hours before dawn on Sunday.
The Orionids, which happen every October like clockwork, have a famous source. The Earth is passing through the orbit of Halley's Comet -- and even though the comet itself is far away, headed toward the outer reaches of the solar system, debris from it has spread out along its path.
The comet itself should be a sight to see if you can hang on for its next pass in the summer of 2061, but in the meantime it gives us this weekend's meteor shower -- shooting stars, usually caused by specks of rock or ice, no larger than grains of rice, plowing into the upper atmosphere at up to 150,000 miles per hour and burning up.
"Since 2006, the Orionids have been one of the best showers of the year, with counts in some years up to 60 or more meteors per hour," said Cooke. "If you don't want to wait until 2061, this is a way to see a bit of Halley's Comet."
The Orionids appear to come from the constellation of Orion the hunter, which dominates the evening sky in the Northern Hemisphere in late fall and winter.
In general, there are more shooting stars in the morning hours because the morning side of the Earth faces forward as we orbit the sun, so it's less shielded. While the shower actually peaks Sunday morning for the U.S., meteors are often spotted several nights before and after.
The best way to watch them is to find a nice, dark place with no street lights and as few trees as possible, and look up. You may want to bring a lawn chair or a blanket. The streaks may be anywhere in the sky, though they'll all appear to come from the direction of Orion. It should be visible from any place with clear weather.
Conveniently, there will only be a crescent moon Saturday evening, setting well before the meteor shower peaks after midnight.
Be alert; most meteors flit silently across the sky in a second or less, sometimes in spurts. If the weather is poor, go to bed and get some sleep; you can also see the Geminid meteor shower on the night of Dec. 13 or the Perseids next August.
But maybe you'll get lucky and see another fireball like the one that surprised Californians. You'll have the satisfaction of knowing the sky is falling...harmlessly.