This is a story about a Frenchman with a long name, Venus and predictable
and unpredictable future.
In the year 1627 the German astronomer Johannes Kepler published his
'Rudolfian Tables'. It was the crown on his astronomical work, dedicated
to his former employer Emperor Rudolf II. This book was based on the new
heliocentric picture of the solar system of a Polish man Nicolaus
Koppernigk (Copernicus) and the accurate observations of planet positions
of a Danish man called Tyge Brahe. Kepler calculated and predicted
(future) positions of the planets. The clockwork of our solar system was
established. And so, Kepler could predict that in 1631 the inner planets
(between Sun and Earth) Mercury and Venus will pass in front of the Sun.
The passage of Mercure was actually observed, but the passage of Venus was
not observable from Europe. The next passage of Venus was predicted by
Kepler to happen in 1761. (Kepler missed an earlier one in 1639).
Until that time, the clockwork of the solar system was known, but not its
dimensions. Only the relative distances between the planets were known,
but not the real distances. The size of the solar system was yet a guess.
The passage of Venus was very important, because with accurate
measurements of this passage from various positions from the Earth (of
which its radius was than accurately known), one was able to calculate the
distance between Earth and Sun. And if this distance was known, all the
other distances were known. So, the year 1761 was a very important year.
And thanks to technological improvements during the former years, accurate
instruments were developed to measure very small angles, and the Dutchman
Christian Huygens had developed the pendulum clock in 1656. Both
instruments were crucial.
The passage of Venus (because of its closer distanc to the Earth than
Mercury) of the 5th of June 1761 was for the entire astronomical community
of utmost importance. The best place for observations of this passage was
in Asia, so astronomers were sent to remote places in Siberia as well as
to the tropical islands in the Indian Ocean. The importance of these
measurements was so great, that even the governments of traditional rivals
England and France (which were involved in one of there regular sea-wars)
decided to give free passage to their astronomers! But unfortunately, this
was not always true.
A French astronomer with the impressive name:
Guillaume-Joseph-Hyacinthe-Jean-Baptiste le Gentil de la Galasiere, was
sent to the French fortification in India, named Pondicherry. Just before
he arrived there, this colony was taken by the English and le Gentil was
not permitted to debark. The poor scientist observed the passage of Venus
in front of the Sun on the cloudless day of the fifth of June, but his
measurements on his wobling ship, floating in the Indian Ocean, were of no
value.
However after the French had retaken Pondicherry, he embarked immediately
again, because he knew that Venus would pass the Sun again in 1769 (these
Venus passages are always in pairs, with 8 years in between).
This next Venus passage of 3rd June 1769 should be best observed from the
American westcoast, the Asian East coast and the yet mainly unmapped
Pacific Ocean. Again, France and England arranged several scientific
expeditions to these regions to observe and take measurements of the Venus
passage. Also James Cook (combining the Venus passage with the race of the
discovery of the "Terra australis incognita" ; the first discoverer could
claim the land) on his first world tour, he observed the passage from the
isle of Tahiti. After Tahiti he discovered New Zealand and the eastcoast
of Australia and became famous.
But what happened with our poor Frenchman? He waited patiently 8 years in
the far east. He travelled on his own initiative farther to the east from
Pondicherry to Manila on the Philipines. He hoped that Manila was the
perfect place to do his accurate observations. However, the French Academy
of Science suggested him to return to Pondicherry (probably because of
political arguments). Keep in mind that such communication took several
months; there was no telephone, fax, or e-mail yet). So he did return to
Pondicherry. Ironically, he received all cooperation from the nearby
English in Madras to observe the longwaited passage. The very day of 3rd
June 1769 started beautiful: an unclouded sky, the sun was shining nicely
as all the former days. But just before the long waited moment of the
passage, a heavy thunder storm started and lasted during the complete
passage of Venus. Nothing was seen! Afterwards, le Gentil was told that in
Manila it was a perfect cloudless day.
When le Gentil completely desillusionised finally arrived in France (after
two times been ship wrecked) in 1771, it appeared that everyone at home
thought that he had died already. His place in the Academy of Science was
meanwhile occupied by a new member, and all his posessions had been
distributed among the heirs.
This is maybe the best example of Murphy's Law.
The next passages of Venus were in 1874 and 1882. Again a lot of
scientists made observations. Communication (the just invented telegraph
enabled world-wide communication within hours) and transportation (the
Suez Canal opened in 1869) made scientific life much easier. In 1890 the
American Simon Newcomb combined all the observations and calculated the
distance Earth-Sun as 149.60 million (10^6) kilometres. At present the
average distance Sun-Earth (the accepted astronomical length unit) is
fixed at: 149597870.660, with an accurancy of only some metres!
Most of us may probably have luck. The next passages of Venus will be 8th
of June 2004, and 6th June 2012. However most of the Americans should
travel than to Europe, India, or Africa. This is what can predicted. What
we not know are the weather conditions. There are too much butterflies on
this Earth.
And another tip: for those of us who are overweighted, check your weight
at these days. :-)
dr. Leo D. Minnigh
minnigh@library.tudelft.nl
Library Technical University Delft
PO BOX 98, 2600 MG Delft, The Netherlands
Tel.: 31 15 2782226
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Let your thoughts meander towards a sea of ideas.
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--Leo Minnigh <L.D.Minnigh@library.tudelft.nl>
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