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How the transit of Venus opened the planet to our forefathers

Author Mark Anderson of 'The Day the World Discovered the Sun' explains how the transit of Venus allowed 18th-century astronomers to create an early GPS system.

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A: Once you got to these far-flung locations, you could time – down to the second – the  duration of how long it takes for Venus to pass over the sun. It was about six hours, but it varied depending on where you were on earth. They had to send people to Arctic locations and tropical locations to get as different a set of answers as you could get.

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When you measure it down to the second, then you can answer these sorts of astronomical, scientific, and even philosophical questions.

Q: How did the astronomers time the transit so efficiently before they had modern clocks?

A: They would take these big, hulking pendulum clocks with them. Once you landed and set up shop, one of the things you get set up is the pendulum clock. Then you can get a very accurate reading, down to fractions of a second.

Q: Were they like grandfather clocks?

A: Grandfather clocks are quaint versions of the precision clocks.

Q: What drew you to this story?

A: Books talk about the science and all these voyages, yet the thing that I found most wanting in all these stories was just a simple answer to the question why. Why did all of these people risk their lives, why did kings and emperors write checks for the equivalents of millions of dollars to send these voyages halfway across the planet?

The answer: The astronomers were providing the kings with the keys to the world, the solution to navigation. It wasn't just about the scientific question, although it motivated the scientists themselves. It was also about what you might call the founding-father era’s military industrial complex.

It was so fundamentally tied into these matters of the utmost national interest and national security matters. To say it was about life and death on the high seas is no exaggeration. If you can’t find the shore, then before morning is light, your ship could be dashed on the rocks.

Q: You had to see the sun to see Venus wander across it. If it was cloudy on that one day, were you doomed?

A: Yes, in so many words.

I don’t really delve into those stories, as they don’t provide a very satisfying resolution. But there was a Frenchman, this poor guy, who is the sad sack of these whole crazy, decade-long odysseys.

In 1761 (during another transit of Venus), he shipped off to India, but he discovered when he got there that his colony had been taken over by the Brits, and he had nowhere to land.

He stuck around for eight more years and finally found a satisfactory place to be on June 3, 1769. But he got nothing that time either. He'd spent a large chunk of his professional career chasing the transit of Venus, and he found nothing.

Q: What do the 1769 voyages mean in the big picture?

A: They really represent the first time that science has traversed national borders and has collaborated, not by a few here and there, but by the dozens and scores and all across the planet in the service of a singular set of goals.

For more about this year's transit of Venus, try NASA or Anderson's website.

Randy Dotinga is a Monitor contributor.

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