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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.
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