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European Space Agency

Press Release

Mercury shows its dark side

2 May 2003
 
During the morning of 7 May 2003, the planet Mercury will slip across
the face of the Sun in a rare event, known as a transit. There are
only about 12 celestial alignments like this every century and you
cannot view them safely without special telescopic equipment. So, let
the ESA/NASA solar watchdog, SOHO, do all the hard work for you... 
 
About 160 times smaller than the apparent diameter of the Sun,
Mercury will appear as a tiny dot, silhouetted on the bright face of
the Sun, as it makes its five and a half hour journey on 7 May 2003.
The show will begin at 9:50 CET (7:50 UT) and last into the
afternoon, finishing at 15:17 CET (13:17 UT). Images of the event
will appear on the SOHO web site as soon as possible, during that
day. Mercury is already visible in the LASCO C3 images on 2 May 2003,
edging closer to the Sun.

The planets Mercury and Venus have orbits closer to the Sun than the
Earth. They are therefore the only planets that can pass in front of
the Sun, as seen from Earth. During the 19th century, transits were
used to precisely measure the distance to Mercury and Venus.
Scientists will use the transit on 7 May 2003 as a unique opportunity
to better understand the instruments on the SOHO spacecraft.

Bernhard Fleck, SOHO's Project Scientist, says, "Our science will be
significantly improved because the transit allows us to better
characterise our instruments." This characterisation will include
precise measurements of the spacecraft's roll angle in space, subtle
image distortions, and an investigation into the effects of stray
light, which contaminate the science images.

Note to Editors: 

The transit will unfold on the internet at:
http://soho.nascom.nasa.gov/hotshots/2003_05_07/The best instruments
to look at are EIT and MDI. 

A much rarer Venus transit will occur on 8 June 2004. The last one
took place in 1884. Unfortunately, it will not be visible from SOHO.

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