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Mercury Transit on November 8, 2006
News story originally written on November 6, 2006

The planet Mercury will cross in front of the Sun on Wednesday, November 8, 2006. Astronomers call the event a transit. A transit is like a solar eclipse. However, a transit occurs when a planet, instead of Earth's Moon, passes between the Sun and Earth. Planets are much further away than the Moon, so the planet does not completely cover the Sun during a transit like the Moon does during an eclipse.

Transits of Mercury happen about once every seven years on average. There will be 14 transits of Mercury this century. This one was the second. The last transit of Mercury before this one was on May 7, 2003. The next won't be until May 9, 2016.

Only two planets ever transit the Sun as viewed from Earth. The two planets are Mercury and Venus. All of the other planets orbit the Sun further from Earth and never pass between Earth and the Sun.

Transits of Venus are much rarer than transits of Mercury. Venus transits happen only twice per century. Maybe you saw the one on June 8, 2004. If not, the next transit of Venus is coming along in just a few years on June 6, 2012! Astronomers in the 1700's used transits of Venus to make the first good measurements of the distance between Earth and the Sun. They did that by carefully measuring the time of the transit from different places on Earth.

Last modified November 6, 2006 by Randy Russell.

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