Transit of Venus: How rare astral event helped astronomers measure the solar system

Transit of Venus
This June 8, 2004 file photo shows the transit of Venus.
AP Photo/Vincent Yu, file

(CBS News) - We have a chance to see something tomorrow that we will never see again. It's called a transit of Venus: Venus will pass between the Earth and the sun, appearing as a small dot moving across the solar surface.

It won't happen again for another 105 years, but it's an event that has mesmerized scientists for centuries.

For astronomers, it's a twice-in-a-lifetime spectacle Last seen in 2004, the next transit of Venus which won't happen until the twenty-second century. But in the 1700s, the transit ignited the first great space race: the quest for a yardstick of the heavens.

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"In the 18th century, astronomers believed that they could use the transit of Venus to answer one of the most pressing questions of the time -- which was the size of the solar system," said Andrea Wulf, author of "Chasing Venus: The Race to Measure the Heavens." "But they also knew their measurements would improve navigation, which was, of course, important for a trading empire or naval power."

Learn more about the transit of Venus

Scientists decided that by measuring the timing and angles of Venus crossing the sun from various points on Earth, that they could calculate the distance from Earth to the sun.

But this triangulation required dispatching hundreds of astronomers from nearly a dozen different nations to far-flung corners of the globe. They dragged cumbersome equipment to the Arctic Circle, the tip of Africa, and Siberia.

Traveling to such exotic locales, the astronomers endured "Everything basically," Wulf said. "Very vicious hostile environments: Tropical storms, hurricanes, you know, freezing temperatures."

Captain James Cook's first voyage to Tahiti was a mission to record the transit.

In Philadelphia, inventor David Rittenhouse was obsessed with planning for the transit. His written recording of the 1769 transit was a great success -- except for a mysterious 15-minute gap.

"He's so excited that when Venus finally appears on the Sun -- he faints," Wulf said, "missing the beginning of the most important scientific moment of his life."

Those 18th century measurements were, in fact, pretty close. They projected the distance to the sun as between 92 and 97 million miles. The actual distance, we now know, is 93 million miles.

  • Elaine Quijano
    Elaine Quijano

    Elaine Quijano was named a CBS News correspondent in January 2010. Quijano reports for "CBS This Morning" and the "CBS Evening News," and contributes across all CBS News platforms. She is based in New York.