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Old 01-06-2004, 15:16   #1
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Trabsit of Venus

Venus to make rare crossing of sun

The planet Mercury crossed in front of the sun in 2003. Venus will make a similar journey on June 8 this year.

NEW YORK (AP) -- Ben Franklin watched it. Sousa named a march after it. Crowds jammed the sidewalks of New York to see it in 1882. But nobody alive today has ever seen the silhouette of Venus crawl across the face of the sun.

On June 8, that sky show -- astronomers call it a transit of Venus -- will return for the first time in 122 years, visible from much of Earth. Thousands of schools and hundreds of museums have set up special programs, and tours to good viewing sites have been booked. Even people who don't want to leave their homes will be able to follow a live Webcast from Greece.

All this to watch a black dot inch across the lower part of the sun. It takes six hours.

"It's kind of slow and boring," says astrophysicist Neil deGrasse Tyson, director of the Hayden Planetarium at New York's American Museum of Natural History.

However, he said, Venus transits carry "incalculable" historical significance.

In the 18th and 19th centuries, these events let scientists probe what one contemporary called "the noblest problem in astronomy:" determining the distance from Earth to the sun. That in turn could be used to figure the distances to all the planets.

Though that problem was eventually solved with precision by other means, the Venus transits produced the first relatively solid estimates and inspired international scientific efforts and rivalries.

It was "the 19th-century equivalent of the space race," said Steven Dick, chief historian for the National Aeronautics and Space Administration.

So, Tyson said, watching a Venus transit nowadays is like linking up to history by visiting a historic site. "I think you can bask in that," Tyson said. "I will."

What's more, a lot of people just want to see something nobody alive has seen before, said Roger W. Sinnott, a senior editor at Sky & Telescope magazine. His magazine has three tours going to Italy, he noted, and the first sold out in 24 hours when it was offered last August.

There's a good reason for interested Americans to go to Europe. The western United States won't be able to see the transit, and the rest of the country will be able to see only the last couple hours or less, starting at sunrise.

The entire six-hour event will be visible from Europe, the Middle East and most of Asia and Africa. Viewers won't need a telescope or binoculars, but scientists warn against looking at the sun without adequate eye protection, just as with a solar eclipse.

During the 1882 transit, amateur astronomers on the streets of New York City sold peeks through their telescopes at 10 cents a shot, noted Sten Odenwald, an astronomer at NASA's Goddard Space Flight Center in Greenbelt, Maryland. The transit became a theme for parties, and it made the front pages of newspapers.

The prospect of measuring the Earth-sun distance made Venus transits a big deal for scientists as well in the 18th and 19th centuries. The idea was to make detailed observations from far-flung places around Earth. Using that data, scientists reasoned, they could do geometric calculations to get the answer.

Scientists carefully observed the four transits from 1761 to 1882. The first -- which revealed that Venus had an atmosphere -- was studied by observers who'd dispersed to 117 posts around the world. Captain James Cook viewed the 1769 transit from Tahiti. In 1874, Russia launched 26 expeditions, Britain a dozen and the United States eight. France, Germany, Italy and Holland sent out parties of observers as well.

Technical problems made it impossible to gather highly precise data. But William Harkness, director of the U.S. Naval Observatory, concluded in 1894 that Earth was about 92.8 million miles from the sun. By then, more accurate methods of determining the distance had arisen, and scientists soon adopted a slightly different value that owed little to Venus transit observations. Today the distance is known to be 92.96 million miles.

Harkness is still remembered for his poetic reflection on the upcoming event. In 1882 he noted that it would occur when "the 21st century of our era has dawned upon the earth, and the June flowers are blooming in 2004."

The next Venus transit after the upcoming one, by the way, will appear when the June flowers are blooming in 2012.

Transit Tips

Most space experts consider viewing a total eclipse with the naked eye safe but stress that partial eclipses, including partial eclipse phases before and after a total eclipse, should only be observed with certain safety precautions to prevent possibly serious eye damage.

Specialized sun filters or strong welder's glasses can protect the eyes. Also, viewers can use a simple indirect method to watch the silhouette of the eclipsing sun as it waxes and wanes through partial phases.

To do so, aim sunlight through a homemade pinhole camera or something else with a pinprick hole in it. Guide the focused sunlight onto a white background such as a sheet of paper. Of course, don't look through the hole directly at the sun.
Gord May
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