Tuesday's rare transit of Venus won't be seen again for 105 years

Published: Friday, June 1 2012 3:14 p.m. MDT

English astronomer William Crabtree was one of the first people to use a telescope to observe the Dec. 4, 1639, transit of Venus. The telescope had only been invented about 25 years earlier. Crabtree used a device that reflected sunlight into a telescope that intruded into his home and projected an image of the sun onto a screen.

Clark Planetarium

SALT LAKE CITY — The solar eclipse has come and gone, but another solar extravaganza is about to happen.

On Tuesday, June 5, people on much of the globe, including Utah, will be able to observe an extremely rare transit of Venus — when Earth's neighboring planet will spend hours in silhouette as it crosses the face of the sun.

"Some people are really fascinated by it and other people aren't," said Fairview resident Ben Gauthier, who's been trying to capitalize on the upcoming event by selling leftover eclipse glasses on sidewalks in downtown Salt Lake City. He bought a supply of them after the May 20 eclipse for 50 cents each and is selling them for $2. He's finding it to be a hard sell because few people are aware of the upcoming event.

The event won't be as thrilling as last month's "Ring of Fire" eclipse that drew tens of thousands of people to southwestern Utah. But for Utahns with an appreciation for the history of science, it's a once-in-a-lifetime opportunity. Or, more accurately, a twice-in-a-lifetime event because the transit occurs in pairs every century or so.

The last one was in 2004; the next one will be 105 years from now in the year 2117.

"You'll be able to see this little bitty (dot). It's not going to be spectacular, but you'll see this little dot," said NASA Ambassador Patrick Wiggins.

The transit will begin just after 4 p.m. Tuesday and it will continue until the sun sets in Utah, according to Seth Jarvis, director of Clark Planetarium.

Those who see it will be sharing in a spectacle that, in the 1760s, triggered the first great international science effort and changed humankind's view of the cosmos. "It has been referred to as the Apollo program of the 18th century," Jarvis said.

Four transits ago, in 1769, government officials and scientists organized expeditions to every corner of Europe and too many other parts of the globe. "It was the biggest, most massive, international scientific cooperative effort ever seen before," he said.

"Prior to this, no one really understood the size of the solar system," Jarvis said.

Scientists of that day realized a transit of Venus could solve that great mystery. They knew if precise measurements were made from all over the globe, basic trigonometry could reveal the scale of the heavens.

The plan for worldwide observations was proposed decades earlier by famed astronomer Edmond Halley, who died long before the transits of Venus in 1761 and 1769.

Scientists in the 1760s went to extraordinary lengths and suffered incredible hardships to observe the transits from widely separated viewing points around the globe. Not enough data was collected during the 1761 transit, so an even larger effort was mounted in 1769.

Famed sea explorer Capt. James Cook was commissioned to undertake his legendary three-year voyage to the South Seas specifically to observe the 1769 transit from the shores of Tahiti.

Wiggins once visited Venus Point in Tahiti where Cook set up his observatory. "And now today, what do we do? We can beam a radar signal off of Venus and tell us exactly how far it is," Wiggins said.

Today the distance from Earth to the sun is known to be 93 million miles. In 1769, the answer scientists came up with was 60 million miles. While the calculation was off, in the 18th century "it was more than 10 times farther than anyone thought," Jarvis said.

"They got it in the ball park. And people (in the 18th century) are now rocked back on their heels and going, ‘Holy cow! Space is big!'" he said.

It's partly because of that rich history that many science enthusiasts don't want to miss what will almost certainly be their only chance to see a transit of Venus. "It is history, history kind of in the remaking," Wiggins said. "And I want to be part of that."

Observers of the transit need to take precautions to protect their eyes just as they did during last month's solar eclipse. Science organizations are once again setting up numerous viewing locations where experts will be on hand with telescopes and solar filters.

E-mail: hollenhorst@desnews.com

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