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On February 15, 2013, a meteor exploded in the air over Chelyabinsk, a region in southern Russia. Unlike many space rocks, which astrophysicists can predict will enter Earth’s atmosphere, the Chelyabinsk meteor was undetected before it screamed across the sky.
 
The Chelyabinsk meteor was part of the Apollo group of asteroids, about 240 space rocks that orbit the sun between Mercury and Earth. The meteor was fairly small, between 17 and 20 meters (56 and 66 feet) in diameter with a mass of about 11,000 metric tons (12,125 short tons) when it entered Earth’s atmosphere. It raced through the atmosphere at about 66,960 kilometers per hour (41,000 miles per hour)—nearly 60 times the speed of sound. This speed led to most of the meteor burning up in the sky, causing a fireball briefly brighter than the sun. The largest chunk of charred Chelyabinsk meteorite, recovered from the icy waters of Lake Cherbarkul, was only 654 kilograms (1,442 pounds).
 
Most of the 1,400 injuries associated with the Chelyabinsk meteor were not a direct result of the meteor, but of the shock wave that followed. The shock wave caused windows, roofs, and walls to shatter and collapse.
asteroid
Noun

irregularly shaped planetary body, ranging from 6 meters (20 feet) to 933 kilometers (580 miles) in diameter, orbiting the sun between Mars and Jupiter.

astrophysicist
Noun

person who studies the relationship between matter, energy, motion, and force outside the Earth's atmosphere.

Noun

layers of gases surrounding a planet or other celestial body.

char
Verb

to burn.

Noun

rocky debris from space that enters Earth's atmosphere. Also called a shooting star or falling star.

Noun

type of rock that has crashed into Earth from outside the atmosphere.

Verb

to move in a circular pattern around a more massive object.

Noun

any area on Earth with one or more common characteristics. Regions are the basic units of geography.

shock wave
Noun

moving, measurable change in pressure and density of a material.

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