Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2006 March 28
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Animation of Asteroids Passing Near Earth
Credit: MPC, Harvard-Smithsonian CfA, IAU

Explanation: How often does an asteroid whiz by the Earth? The above time-lapse animation follows the orbit of the Earth around the Sun for two months in 2002 as numerous asteroids, also known as minor planets, approach and pass by. Some asteroids appear out of nowhere as they are plotted only when they were discovered. Most asteroids plotted were discovered only during the previous year. Although none of the plotted objects came inside the orbit of our Moon, our Solar System is filled with objects as small as bits of sand, usually left by a comet, that appear as meteors as they streak into the Earth's atmosphere every day. The only objects displayed are those visible from Earth closer than 20 million kilometres, colour coded by three-dimensional distance. In comparison, the Earth is a relatively small target having a radius of about 6,400 kilometres. One significant research area in modern astronomy involves trying to find the majority of asteroids that could pose a future collision threat with Earth.

Tomorrow's picture: aurora sky

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