Guillaume Le Gentil and the Transit of Venus

Tonight at approximately 6:00 PM New Yorkers may be able to witness a portion of the transit of Venus across the face of the sun. The full transit will take approximately seven hours, so our sun will set before we can observe the entire event.  It will be the last time in our lifetimes (barring some miraculous medical advances) that a transit will occur.  Transits of Venus happen in a strange pattern – there are two transits eight years apart and then the next transit occurs  105 or 121 years later.  There was a transit in 2004 and after tonight, the next one will happen in 2117. See Wikipedia for more information on transits.

Early astronomers figured out that by carefully timing when a transit began and ended at different points on earth, they could calculate the distance between the earth and the sun and other celestial bodies.  The Europeans got serious about this in the 18th century and sent out astronomers to far-flung parts of the world to measure the transits of 1761 and 1769.

When I took Astronomy 1101 with Professor Matloff (a fantastic course I urge you to take as your science with lab requirement), he told us the greatest story about a French astronomer named Guillaume Le Gentil.

Click for source.

Click for source

In 1760, Le Gentil left France for Pondicherry, India to time the 1761 transit there.  Poor Le Gentil – a war had broken out between the French and British in Pondicherry and he was never able to get off various boats and build the observatory he needed to time the transit.  On the day of the 1761 transit Le Gentil was stuck on a ship and couldn’t measure squat.

So Le Gentil decided to stick around India and wait for the next transit eight year later.  Imagine that dedication to science!   Eventually, peace was restored in Pondicherry and Le Gentil was able to build his observatory .

Can you guess what happened in 1769?

There was a storm on the day of the transit – Le Gentil couldn’t see the sun!  He couldn’t measure squat. AGAIN.  To make him feel even worse, the sun came out right after the transit had ended that day!  You can read a wonderful account of Le Gentil’s misadventures at The Ordeal of Guillaume Le Gentil.

Le Gentil had a rough time getting back to Paris too.   After having been gone eleven years altogether, he returned to find that he’d been declared dead, his wife had re-married, his estate had been plundered and he’d lost his job!

They are predicting clouds in New York City for today’s transit. There are many of us who have been in a tizzy awaiting this transit and  we all  may get a taste of Le Gentil’s disappointment tonight.   The good news for us is that we can watch the transit online because somewhere on earth it is bound to be sunny!  Live or online, I’ll be remembering Le Gentil tonight.






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