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Mercury (the dark circle) near the edge of the Sun during the transit.
Click on image for full size
Image courtesy of The Royal Swedish Academy of Sciences.

Mercury Transit on May 7, 2003
News story originally written on July 2, 2003

The planet Mercury crossed in front of the Sun on May 7, 2003. When that happens, astronomers call it a transit. A transit is like a solar eclipse. An eclipse happens when the Moon passes in front of the Sun. A transit happens when a planet passes in front of the Sun. Planets are much further away than the Moon, so they look much smaller. A planet does not completely cover the Sun during a transit like the Moon does during an eclipse.

There will be 14 transits of Mercury this century. This one was the first. The last transit of Mercury before this one was in 1999. The next will be on November 8, 2006.

Only two planets ever transit the Sun. The two planets are Mercury and Venus.

Transits of Venus are very rare. They only happen about two times every 100 years! In the 1700's astronomers used transits of Venus to make the first good measurement of the distance between Earth and the Sun.

Last modified July 2, 2003 by Randy Russell.

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