Tuesday, June 5, 2012 |
Late this afternoon, or early this evening on June 5 (depending on where you are in Canada), Venus will pass directly between the sun and the Earth. This is known as the Transit of Venus, and it only occurs twice a century, eight years apart. The last Transit was in 2004 and the next one won't be until 2117. Although they are a minor curiosity for today's astronomers, the Transits in 1761 and 1769 attracted the attention of leading astronomers of the day, who sought to measure the phenomenon in order to calculate the distance from the Earth to the sun. Dozens of expeditions, led by Europe's leading astronomers, were sent out on this quest in 1761 and 1769. Science journalist Mark Anderson chronicles the most successful and most challenging journeys in his new book, The Day the World Discovered the Sun.
Anderson wanted to capture this moment in scientific history because of the significant advances astronomers were making in navigation. Expeditions were failing because captains had no idea how far their destinations were and would often run their ships aground on shoals, rocks and shores. In other words, they could not accurately measure longitude. "Astronomy was the way through to solving this deadly problem," Anderson told Quirks & Quarks host Bob McDonald in a recent interview. Astronomers did so by developing a system that used "the moon as the GPS satellite" to determine geographic location. "It was nothing short of revolutionary because it was the place-finding science that allowed navies to cross the oceans, that allowed merchant fleets to get to ports. In some ways, it really changed the world." The Transit of Venus voyages offered the perfect opportunity to test this new system, alongside accomplishing another important task: measuring the distance of the Earth from the sun. Anderson chose to focus on three of the most successful journeys in 1769 because he wanted readers to "relate to individual characters and follow individual story-lines" and wanted to share "really amazing characters and incredible adventures."
The first of these trips was the career-making voyage of James Cook, who led an excursion to Tahiti. The Royal Society and the Admiralty of England contacted the relatively unknown naval commander with a proposal for a new voyage with three distinct purposes. First, he had to test the new navigation system that used the moon to determine geographic location. Second, he had to measure the Transit of Venus from the tropics. Third, he had to find the "long-lost southern continent" believed to be in the southern hemisphere. Cook completed the first two tasks, despite many obstacles. When he arrived in Brazil, his crew was kept "under lock and key" because a Portuguese viceroy "figured that this was an undercover espionage mission." He eventually let Cook and his crew go and they made their way to Tahiti, where their astronomical instruments were frequently stolen by the local populations. While he failed on the third goal, he successfully mapped much of the east coast of Australia and New Zealand, and these maps were used well into the 19th century.
The second voyage in The Day the World Discovered the Sun was the voyage of French astronomer Jean-Baptiste Chappe d'Auteroche, who navigated his way to the Baja Peninsula in present-day California. Chappe d'Auteroche also faced immense challenges getting to his final destination. Since his voyage was a combined French/Spanish expedition, the Spanish military was very nervous, and the expedition was tied up in bureaucracy to the point "they were running so late that they had to just take any ship that would carry them across the Atlantic," Anderson said. When they finally arrived in "New Spain," a hurricane hit and "they almost lost everything." After a difficult journey across Mexico that saw them facing difficult terrain, starvation and disease, they finally "landed with just a few days to spare," only to face a massive typhus outbreak. "They were all willing to lay down their lives for the sake of getting this one number."
The final voyage Anderson writes about is the trip to the Norwegian Arctic led by Hungarian priest Maximilian Hell and his assistant János Sajnovics, who were, according to Anderson, "like the Odd Couple. It was high drama and high comedy all at once." Anderson chalks their differences up to Sajnovics' strong personality. "Imagine sending someone who loves fine wine and dining up to a remote Arctic outpost in the 18th century."
Despite the troubles all three journeys faced, each was successful in collecting the data required, a feat Anderson finds remarkable. "This is an age where the fastest anyone in human history had gone was the speed of a fast ship or a fast horse. The highest that anyone had ever gotten ... was a cathedral spire. And yet in these very humble times, people could inch out a measuring line into the solar system and measure with this incredible accuracy," he said. "It's truly remarkable."