The planet Venus is seen crossing the sun in June 2004 as photographed through a telescope at Planetarium Urania in Hove, Belgium. The earliest known observation of such a transit was in 1639 by English astronomer Jeremiah Horrocks. Geert Vanden Wijngaert/AP hide caption

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Geert Vanden Wijngaert/AP

Venus on the eastern limb of the Sun captured by TRACE satellite. NASA hide caption

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The Venus Transit: Who Cares?

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Safety over style: In 2006, a Palestinian man and boy were careful to protect their eyes while watching a partial eclipse of the sun. The same cautions are in order for Venus' transit of the sun on Tuesday. Saif Dahlah /AFP/Getty Images hide caption

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Saif Dahlah /AFP/Getty Images