Saturday, June 23, 2012
Evotour, part five. The Transit of Venus, or, Guillame LeGentil Finally Gets Satisfaction
The Transit of Venus occurs when Venus moves across the face of the sun, as seen from the Earth. This event occurs only in eight-year pairs, each pair being separated by 121.5 and 105.5 year intervals. The last transit was in 2004, eight years ago. The next pair will be in 2117 and 2125. So as the sun sank into the Pacific Ocean, from my terrestrial viewpoint, I knew that none of us alive now would ever see it again.
Why is the Transit of Venus such a big deal? The Transit of Venus was first observed by Jeremiah Horrocks in 1639. At that time, the heliocentric view of the solar system (planets revolving around the sun) was as new of an insight as evolution is today, so it must have been exciting just to see visual confirmation of it, just as people today express surprise at seeing evolution in action.
By 1761, scientists were ready to observe the transit from different parts of the world. Scientists were stationed in Siberia, Norway, Newfoundland, Madagascar, and the Cape of Good Hope in order to determine the exact times at which Venus began, and ended, its transit. It takes long enough that the entire transit cannot be observed from any one location. By using triangulation, the scientists would then be able to determine how far away the sun is, and from that they could calculate the orbits of the planets. In 1769, scientists were at Hudson Bay and Norway, and Captain Cook observed it in Tahiti at a place that is now called “point Venus.”
What does this have to do with evolution? Back in the middle ages, scholars thought that the sun, stars, and planets were on spheres that turned around the Earth. God had created these spheres as part of the perfect machinery of the cosmos. Part of this image is that the planes of revolution of all the planets would line up precisely. Were this the case, then there would be a Transit of Venus every year. But the planes of revolution of Earth and Venus are not parallel. The sun, Venus, and Earth line up only at rare intervals. This was the beginning of the end of the concept that God had perfectly designed the universe, creating what scholars at the time literally considered to be the harmony of the spheres. The theories of geology and then of evolution further undermined the Perfect Design view, a concept that has been demolished by modern genetic research.
The French scientist Guillame Le Gentil traveled to India to see the 1761 transit. When he arrived at Pondicherry, the French enclave in the subcontinent, he found that war had broken out and the ship could not land. The day of the transit was clear, but the lurching of the ship prevented him from seeing it. So he decided to stay and see the 1769 transit. He built an observatory (after the hostilities had ceased). For a month before the transit, every day was clear—until the day of the transit, which was cloudy. The disappointment drove him nearly to the brink of insanity. He went home to France, only to find that he had been declared legally dead, his property had been divided up, and his wife had remarried. Most important of all to Le Gentil, he had lost his post in the Academy of Sciences. But after the intervention of the king, Le Gentil was able to get back some of his property. He remarried and lived another 21 years. Best of all, he was reinstated in the Academy.
But Le Gentil never got to see the Transit of Venus. Until this year.
I met two scientists from the University of California at San Diego—one an orthopedic anatomist (J. R. Bachman), the other an anthropologist, both amateur astronomers—who were walking up to the top of Stonewall Peak in Cuyamaca Rancho State Park in California on June 5. They were toting their telescopes, and a bunch of computer printouts. They were going to celebrate the transit by creating living art, projecting the solar disc onto portraits of astronomers. One was Guillame Le Gentil. They had cut out a hole in his eye, so that he could at last see the transit and, perhaps, rest in satisfaction.
I have to apologize because, no matter how my photographic file is oriented, Blogger insists on turning it sideways, and there appears to be no option for setting it right.
Another pair of transits occurred in 1874 and 1882. John Philip Sousa wrote a march, the Transit of Venus, for the 1882 event. And Mark Twain put it in a story, The Animals of the Forest Conduct a Scientific Expedition. Wild animals decided to investigate the human world as we investigate theirs. They encountered a train running along its tracks at night, with its headlight on, and they concluded that it must be the Transit of Venus.