9. Mercury Transits Sun

Mercury was a mere dot against the bright Sun when it crossed the solar face, as seen from Earth on May 7. Transits like this are rare -- only about 13 each century.

This time around, the Internet was ready. Several organizations ran live webcasts showing the event in progress. A Royal Swedish Academy of Sciences telescope made this picture.

An even rarer type of transit will occur in 2004, when Venus makes its first walk across the Sun since 1882. That exciting moment will come June 8.

[Story and larger version of image]

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