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.

By Randy Dotinga / May 25, 2012

The planet Venus will dart across the sun on June 5 ? but don't look for it unless you have the proper equipment.

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Last weekend, many of us here on the West Coast dabbled in a bit in astronomy during a partial eclipse of the sun. With the sun low on the horizon, I stole a quick glance to see if I could glimpse a shadow.

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Yup, I did. And then I saw something else: stars. My eyes!

My advice: Do not try this at home. And definitely don't even think about it at around sunset ET on June 5, when the planet Venus will do something really unusual. It will dart across the sun, and much of the world will be able to watch it make its move with the right (and safe) equipment.

It's called the transit of Venus. The planet will appear as little dark circle on the sun as it zips between us and that big yellow ball.

If you want to catch it, hope for a clear sky because you won't see it again. About every 120 years or so, transits of Venus come in clusters ? two in eight years. The last one was in 2004, and we won't see another until well into the 22nd century. Astronomers long ago figured out when the transit of Venus would occur, and they discovered that timing it down to the second would give them tremendous insight into the solar system.

When the event occurred on June 3, 1769, scientists ? including the famous Captain James Cook ? fanned around the globe in an attempt to uncover the secrets of the universe.

In his new book The Day the World Discovered the Sun: An Extraordinary Story of Scientific Adventure and the Race to Track the Transit of Venus, author Mark Anderson uncovers the tales of the men who literally went to the ends of the earth in search of discovery.

In an interview, Anderson talked about the goals of the missions, the way 18th-century scientists managed to measure time to the second (hint: not with an iPhone stopwatch), and how clouds on the big date may be more than just a mood-buster.

Q: What was the big mystery that all these scientists were trying to solve?

A: In two words, it was "how far."

How far is the most important thing in our universe, the sun? And how far would you go to find that answer? Would you be willing to lay down your life? A host of scientists and explorers at this time did just that.

The other question is essential to the story: How far is the shore? That's the other question, the one that ship navigators could not answer. As a result, thousands of people died gruesome deaths at sea by shipwreck or being lost at sea.

These astronomers had invented an 18th-century GPS system that opened up the entire planet to seafaring nations. The voyages were the perfect testing grounds for this new technology.

The cool thing for the story is that to find the answer to both questions, you have to go to the ends of the earth. That sets the stage for an amazing adventure.

Q: How did this one event in the skies provide so much information?

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