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Moscow (CNN) -- A meteor streaked through the skies above Russia's southern Chelyabinsk region Friday morning, before exploding with a flash and boom that shattered glass in buildings and left hundreds of people hurt.

The number of people reporting injuries climbed to more than 500 by lunchtime, according to Vladimir Stepanov, of the National Center for Emergency Situations at the Russian Interior Ministry.

Opinion: Don't count 'doomsday asteroid' out yet

Of those, 22 are hospitalized, he told state broadcaster Russia 24.

About 270 buildings have sustained damage -- mostly broken glass -- as a result of the shock waves caused by the blast, Stepanov said, with hospitals, kindergartens and schools among those affected.

An asteroid is coming! But don't panic. NASA says Asteroid 2012 DA14 will make a record-close pass by Earth on February 15, but it won't hit us. Most asteroids are made of rocks, but some are metal. They orbit mostly between Jupiter and Mars in the main asteroid belt. Scientists estimate there are tens of thousands of asteroids and when they get close to our planet, they are called near-Earth objects.

This graphic shows Asteroid 2012 DA14's predicted path as it passes closest to Earth on February 15 at 2:24 p.m. ET. It will fly 17,200 miles (27,700 kilometers) above Earth's surface and inside the ring of weather and communications satellites. The asteroid is about 150 feet (45 meters) in diameter. It is heading toward Earth at 17,450 mph.

Another asteroid, Apophis, got a lot of attention from space scientists and the media when initial calculations indicated a small chance it could hit Earth in 2029 or 2036. NASA scientists have since ruled out an impact, but on April 13, 2029, Apophis, which is about the size of 3½ football fields, will make a close visit -- flying about 19,400 miles (31,300 kilometers) above Earth's surface. The images above were taken by the European Space Agency's Herschel Space Observatory in January 2013.

If you really want to know about asteroids, you need to see one up close. NASA did just that. A spacecraft called NEAR-Shoemaker, named in honor of planetary scientist Gene Shoemaker, was the first probe to touch down on an asteroid, landing on the asteroid Eros on February 12, 2001. This image was taken on February 14, 2000, just after the probe began orbiting Eros.

The first asteroid to be identified, 1 Ceres, was discovered January 1, 1801, by Giuseppe Piazzi in Palermo, Sicily. But is Ceres just another asteroid? Observations by NASA's Hubble Space Telescope show that Ceres has a lot in common with planets like Earth. It's almost round and it may have a lot of pure water ice beneath its surface. Ceres is about 606 by 565 miles (975 by 909 kilometers) in size and scientists say it may be more accurate to call it a mini-planet. NASA's Dawn spacecraft is on its way to Ceres to investigate. The spacecraft is 35 million miles (57 million kilometers) from Ceres and 179 million miles (288 million kilometers) from Earth. The photo on the left was taken by Keck Observatory, Mauna Kea, Hawaii. The image on the right was taken by the Hubble Space Telescope.

One big space rock got upgraded recently. This image of Vesta was taken by the Dawn spacecraft, which is on its way to Ceres. In 2012, scientists said data from the spacecraft show Vesta is more like a planet than an asteroid and so Vesta is now considered a protoplanet.

The three-mile long (4.8-kilometer) asteroid Toutatis flew about 4.3 million miles (6.9 million kilometers) from Earth on December 12, 2012. NASA scientists used radar images to make a short movie.

Asteroids have hit Earth many times. It's hard to get an exact count because erosion has wiped away much of the evidence. The mile-wide Meteor Crater in Arizona, seen above, was created by a small asteroid that hit about 50,000 years ago, NASA says. Other famous impact craters on Earth include Manicouagan in Quebec, Canada; Sudbury in Ontario, Canada; Ries Crater in Germany, and Chicxulub on the Yucatan coast in Mexico.

NASA scientists say the impact of an asteroid or comet several hundred million years ago created the Aorounga crater in the Sahara Desert of northern Chad. The crater has a diameter of about 10.5 miles (17 kilometers). This image was taken by the Space Shuttle Endeavour in 1994.

In 1908 in Tunguska, Siberia, scientists theorize an asteroid flattened about 750 square miles (1,200 square kilometers) of forest in and around the Podkamennaya Tunguska River in what is now Krasnoyarsk Krai, Russia.

What else is up there? Is anyone watching? NASA's Near-Earth Object Program is trying to track down all asteroids and comets that could threaten Earth. NASA says 9,672 near-Earth objects have been discovered as of February 5, 2013. Of these, 1,374 have been classified as Potentially Hazardous Asteroids, or objects that could one day threaten Earth.

One of the top asteroid-tracking scientists is Don Yeomans at the Jet Propulsion Laboratory, which is managed by the California Institute of Technology. Yeomans says every day, "Earth is pummeled by more than 100 tons of material that spewed off asteroids and comets." Fortunately, most of the asteroid trash is tiny and it burns up when it hits the atmosphere, creating meteors, or shooting stars. Yeomans says it's very rare for big chunks of space litter to hit Earth's surface. Those chunks are called meteorites.

Asteroids and comets are popular fodder for Earth-ending science fiction movies. Two of the biggest blockbusters came out in 1998: "Deep Impact" and "Armageddon." (Walt Disney Studios) Others include "Meteorites!" (1998), "Doomsday Rock" (1997), "Asteroid" (1997), "Meteor" (1979), and "A Fire in the Sky" (1978). Can you name others?

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Photos: All about asteroids

Russian meteor injures hundreds

Read more: Saving the Earth from asteroids

The vast majority of injuries are not thought to be serious.

Amateur video footage showed a bright white streak moving rapidly across the sky, before exploding with an even brighter flash and a deafening bang.

The state-run RIA Novosti news agency cited the national space agency, Roscosmos, as saying that scientists believed one meteoroid had entered the atmosphere, where it burned and disintegrated into fragments.

The resulting meteorites are believed to be scattered across three regions of Russia and neighboring Kazakhstan, the news agency said.

One large chunk was discovered in a lake in the Chelyabinsk region, RIA Novosti cited the Chelyabinsk governor as saying.

Read more: When the Quadrantid meteor shower hit its peak

The explosion was centered about 50 miles (80 kilometers) from Satka city, in the Chelyabinsk region, the state-run Itar-Tass news agency reported.

A spokesman for the Emergency Ministry of Chelyabinsk earlier told CNN the explosion sparked by the meteor injured 247 people there, with nine hospitalized.

NASA estimates 4,700 'potentially hazardous' asteroids

For sky watchers, the reports bring to mind the famous Tunguska event of 1908 in remote Siberia, in which an asteroid entered the atmosphere and exploded, leveling trees over an area of 820 square miles -- about two-thirds the size of Rhode Island.

About 80 million trees were felled, radiating out from the center of the blast, but no crater was left.

Friday's Chelyabinsk meteor comes on the same day that a hefty asteroid is due to charge past Earth at a pretty close range, in space terms.

An asteroid is coming. Fear not, scientists say

Known as 2012 DA14, the asteroid is thought to be 45 meters long, about half the length of a football field.

But scientists say it will come no closer than 17,100 miles from our planet's surface.

Your photos: Orionid meteor shower

"No Earth impact is possible," according to Don Yeomans, manager of the Near-Earth Object Program Office at NASA's Jet Propulsion Laboratory.

Those in Eastern Europe, Asia or Australia will get the best telescope-aided view, scientists said. The asteroid won't be visible to the naked eye.

CNN's Phil Black, Boriana Milanova and Alla Eshchenko reported from Moscow, and Laura Smith-Spark wrote from London. CNN's Elizabeth Landau also contributed to this report.