Amateur videos broadcast on state television showed an object streaking across the sky, trailing smoke, around 9:20 a.m. local time before bursting into a fireball. It caused a sonic boom from which residents in the city of Chelyabinsk, the largest in the affected region, described a shock wave that blew in doors, smashed glass and set off car alarms.

"The light was so intense that it completely illuminated the courtyard of our apartment block," said Sergei Zakharov, head of the Russian Geographical Society in Chelyabinsk. "The sound, the shock wave came around six minutes later. No one could understand what had happened. I'd compare it to the explosion of a large flare bomb."

How many more asteroids are in orbit besides 2012 D414, which passed by Earth on Friday? NASA's Dr. Jim Green joins Digits to discuss. Photo: NASA.

Simon Constable discusses asteroids and meteors with Dr. Denton Ebel, from the American Museum of Natural History, and Jack Hough previews the upcoming issue of Barron's. Photo: NASA.

A meteor flew across the sky over Russia's Ural Mountains, showering fragments of rock over the area and causing explosions. Around 1.000 people were injured by the shock wave, many of them hurt by broken glass. Photo: Associated Press

Prior to the unexpected meteorite strike in Russia Friday, scientists had predicted that a separate asteroid would pass by earth, missing by 17,200 miles, in the closest known fly-by for a rock of its size. Read More.

Almost 1,000 people sought medical attention, mostly for cuts from flying glass, and 43 were hospitalized, the Emergency Situations Ministry said. Around 3,000 buildings were damaged by the blast, which blew a hole in the walls of a metals factory in Chelyabinsk, approximately 900 miles east of Moscow.

Children were sent home from schools, and the explosion temporarily knocked out one mobile operator's network.

A meteor contrail was seen over Chelyabinsk, Russia, on Friday. The meteor streaked across the sky of Russia's Urals, causing explosions and injuring around 1,000 people. Chelyabinsk.ru/Associated Press

The unusual sight sowed confusion among some locals. Amateur video showed children in one school streaming out of a classroom and screaming.

"That kind of light doesn't happen in life, only at the end of the world," Vlada Palagina, a Chelyabinsk schoolteacher, told the LifeNews website.

"We thought an airplane had crashed," said a woman who answered the phone at the city administration.

Officials moved quickly to calm residents, saying there was no threat to human life from the rock fragments that hit the earth outside Chelyabinsk. Most of the meteor burned up before pieces hit the ground, scientists said.

President Vladimir Putin ordered the emergency situations minister to provide help for those affected.

ENLARGE

A hole in the ice marks a place where a meteorite reportedly crashed into a frozen lake outside the city of Chelyabinsk, Russia, on Friday.
Associated Press

"There's no major destruction," Chelyabinsk regional Governor Mikhail Yuyevich wrote on his blog. "The main task now is to maintain heat in the apartments and offices where the glass was smashed."

Scientists said the incident was a rare event, both in terms of the size of the rock and the number of injuries it caused.

"There have been reports of one or two people being injured in the past. This is entirely unprecedented," said Keith Smith, an astronomer at Britain's Royal Astronomical Society.

Asteroids are fairly small pieces of rock that go around the sun. A meteoroid is an even smaller piece of debris or a particle that goes around the sun. A meteor is the light phenomenon we see when a meteoroid burns up as it flies through the atmosphere—what we commonly call shooting stars. A meteorite is a meteoroid that survives its atmosphere plunge and lands on Earth.

ENLARGE

In Russia, dozens of fragments of the meteor hit the ground, officials said, and search teams set out looking for meteorites outside Chelyabinsk.

Local police described how one piece smashed into the ground near Lake Chebarkul, throwing up a column of ice, water and steam and creating a 26-foot crater.

The meteor was several yards in diameter and weighed around 10 metric tons, Russia's Academy of Sciences said in a statement. "The object entered the atmosphere at a speed of 15 to 20 kilometers (9 to 12 miles) per second, disintegrated at a height of 30-50 kilometers. The movement of fragments at large speed caused a powerful emission of light and a strong shock wave," the academy said.

According to the U.S. National Aeronautics and Space Administration, meteoroids smaller than 25 meters usually burn up as they streak through the atmosphere, causing little or no damage.

Earth is bombarded with more than 100 tons of dust and sand-sized particles every day, much of it falling into the oceans or remote areas, and otherwise going unnoticed. About once a year, a car-size asteroid enters the atmosphere, though it usually burns up before hitting the surface.

It is only every 2,000 years or so that an object the size of a football field descends to earth and causes significant damage, according to NASA. Giant asteroids that crash to earth—such as the one that most likely extinguished the dinosaurs—tend to occur on the scale of millions of years.

Scientists will likely rush to the site in Russia where the meteor was observed. Astronomer Dr. Smith said there has probably been only one case—in Sudan in 2007—where researchers were able to follow the track of a meteor as it came down and recover pieces of it on the ground.

Russian Deputy Prime Minister Dmitry Rogozin called for leading world powers to create an early-warning system, and consider technology to shoot down meteors. Roskosmos, Russia's space agency, said it was impossible to track objects falling as fast as the meteor.

This copy is for your personal, non-commercial use only. Distribution and use of this material are governed by our Subscriber Agreement and by copyright law. For non-personal use or to order multiple copies, please contact Dow Jones Reprints at 1-800-843-0008 or visit www.djreprints.com.