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             Information from the European Southern Observatory

 ESO Press Release 10/03

 2 May 2003                                                [ESO Logo]

 For immediate release
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A Solar Mini-Eclipse on May 7, 2003

Planet Mercury Passes in Front of the Solar Disk

A solar mini-eclipse! On May 7, 2003, Mercury, the innermost planet
in the solar system, willpass in front of the Sun and produce a solar
eclipse. But this event will hardly be noticed. Mercury's small disk
will indeed barely be bigger than the point of a pencil. Even the
smallest sunspots on the solar surface are as big as the Earth and
measure 10,000 km or more in diameter, while Mercury's equatorial
diameter is only 4878 km.

Bathed in intense sunlight, this small, hot planet moves around the
Sun in an elliptical orbit at a mean distance of only 58 million km,
much closer to the Sun than other inner planet, Venus (108 million
km) and the Earth (150 million km).

The disk of Mercury is very small and will be very difficult to see.
A powerful telescope is needed to observe this event and to show
clearly how Mercury moves across the solar disk. The disk of Mercury
is indeed only 13 arcseconds across (while the solar disk measures
about 1800 arcseconds).  This corresponds to the size of a 1 EURO
coin located at the top of the Eiffel Tower as seen from the ground.
Therefore, Mercury will only block 1/20,000th of the Sun's light.

Mercury Transits

Passages of Mercury in front of the Sun, or "Mercury Transits" in
astronomical terminology, are comparatively rare events, due to the
different orbital inclinations of the Earth and Mercury as they move
around the Sun.

In order for a Mercury transit to happen, the planet must be located
directly between the Earth and the Sun and also near one of the two
points in its orbit where Mercury's orbital plane intersects that of
the Earth. We then face the dark side of Mercury - the hemisphere
that is not illuminated by the Sun - and see it as a small dark spot
moving across the bright solar disk.

There are about 13 Mercury transits each century and they follow in
time intervals of approximately 13, 7, 10 and 3 years. The most
recent one took place in November 1999 and the next will be on May 7,
2003 and November 8, 2006.

The next Mercury transit happens on Wednesday morning next week. It
lasts from about 7:13 hrs CEST (Central European Summer Time) until
12:32 hrs CEST (5:13 to 10:32 UT) and the contour of the small planet
as it moves across the solar disk can be seen from all places where
the Sun is above the horizon and the sky is clear. The best observing
conditions are from Europe, Africa and Asia.

Observations of the transit

Note, however, that this event cannot be observed with the unaided
eye - this would also be extremely dangerous because the enormous
brightness of the Sun will cause total blindness in a fraction of a
second!

Observations can only be made by means of telescopes which project
the solar image onto a white screen.

Public observatories, planetaria and other educational institutions
will arrange special events on this occasion. News about such
arrangements will appear in the local press.

Live images on the web

On this special occasion and in order to provide for everybody the
chance to watch this event, the European Southern Observatory (ESO)
and the European Association for Astronomy Education (EAAE), together
with the Institut de Mecanique Celeste et de Calcul des Ephemerides
(IMCCE) and the Observatoire de Paris in France, are providing live
images and a running commentary for all interested parties. It is
also planned to display images obtained at observatories in the
Belgium, the Czech Republic, Hungary, Italy and Spain, and possibly
others. The availability will depend on the weather situation in the
various places.

Full information and many weblinks to other educational sites are
available via the special website at:

   http://www.eso.org/outreach/eduoff/vt-2004/mt-2003/mt-intro.html

On this site, extensive background information about Mercury and the
Sun can be found and, in particular, useful sheets for school
students and teachers in many languages. Live images from
professional telescopes (depending on the weather at the observing
sites) will be available on the special webpage:

  http://www.eso.org/outreach/eduoff/vt-2004/mt-2003/mt-display.html

and it will also be possible to ask questions in "real-time" to
astronomers via this page.

Venus Transit on June 8, 2004

The Mercury Transit of May 7 is also a kind of "general rehearsal" to
the even rarer Venus Transit event on June 8, 2004. The last such
event took place in 1884, so that no living person has ever seen
one. The above mentioned organisations are also preparing for a major
public event on that occasion. Provisional information is already
available at the VT-2004 website.

Contacts

Bernhard Mackowiak
ESO EPR Dept.
Garching bei Muenchen, Germany
Tel: +49-89-3200-6322
email: bmackovi{at}eso.org

Jean-Eudes Arlot
IMCCE
Paris, France
Tel: +33-1-40512267
email: arlot{at}imcce.fr

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