The dark disk of Mercury seen against the backdrop of the Sun during the transit. The transit is almost over, and Mercury appears near the edge of the Sun. This picture was taken with the Swedish 1 meter Solar Telescope (SST), which is located at La Palma in the Canary Islands.
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 appeared to cross in
front of the Sun on May 7, 2003. 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 first. The last
transit of Mercury before this one was on November 15, 1999. The next will
be on November 8, 2006.
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. We're in luck though - the next transit of Venus
is coming along pretty soon on June 8, 2004! 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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