Dark matter, one of cosmology's most curious mysteries, has yet to be seen. But theorists have good reason to believe that it exists, and that galaxies, stars, and planets could never have formed without the gravitational attraction that dark matter exerts.
Russians in western Siberia captured video of a visible meteorite that streaked across the sky, early Friday morning. The meteorite caused a shockwave strong enough to shatter glass in a wide area, causing hundreds of injuries.
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