In 2013, NASA's Cassini spacecraft captured this image of Earth from Saturn. Seen here, our planet is 898 million miles away (1.44 billion kilometers) and appears as a blue dot at center right.
NASA/JPL-Caltech/Space Science Institute
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