A WORTHY ENDEAVOR:

Checking Out Venus, but Not Taking Her Measurements: Once Used to Compute Earth-Sun Distance, Planet's 'Transit' Is Still a Great Show (Guy Gugliotta, May 31, 2004, Washington Post)

What a difference 121.5 years make. The last time the planet Venus passed directly between the sun and Earth -- in 1882 -- the Great Powers, as well as upstarts such as the United States, sent scientific teams to the far corners of the globe to observe the event.

Their aim: use the "transit of Venus" to compute the exact distance from Earth to the sun, a problem that had captivated astronomers ever since Aristarchus of Samos made a wildly inaccurate calculation 2,300 years ago. (He did determine -- quite accurately -- that the sun was a long way away.)

In 1882, said NASA Chief Historian Steven J. Dick, "the excitement could be compared to the space race. Any country with an interest in its scientific reputation was involved. It was the thing to do in the 19th century."

On June 8 it happens again. And although astronomers long ago found much better ways of calculating the astronomical unit -- the Earth-to-sun distance, which is reckoned today at 92,955,887.6 miles -- the transit remains an event of great rarity and curiosity.

In the United States, only the last two hours of the six-hour transit will be visible -- and that only in the eastern part of the country, just after dawn. Much of Europe, Africa and Asia, however, will see it all, and astronomy aficionados have mounted numerous expeditions to prime observation spots.

The transit will be visible to the naked eye, but experts caution that looking directly at the sun will cause permanent damage to the eyes. The solution is to project the image with a "pinhole camera" device or to look through a dark filter, either with the eyes alone or with a telescope or binoculars . (For instructions on safely viewing objects crossing the sun, see the Web site http://skyandtelescope.com/observing/objects/eclipses/article_609_1.asp<.)

Your Guide to the Transit of Venus (Editors of Sky & Telescope)

On Tuesday, June 8th, the planet Venus will glide directly across the face of the Sun. No one alive today has seen Venus "transit" the Sun — it last happened in 1882 — and astronomers around the world are eagerly awaiting the event. Only one other transit of Venus will occur this century, eight years from now on June 6, 2012.

During this 6-hour-long event, Venus will appear as a perfectly round black dot slowly moving across the Sun's face. The most interesting times will be when Venus enters and exits the outer edge of the solar disk, each taking about 20 minutes to complete. For observers in eastern and central North America, the Sun rises on June 8th with the transit already well under way. The entire event will be visible from Europe, central/eastern Africa, the Middle East, and Asia (except the Far East). Numerous groups will be broadcasting the event over the Internet; here are several Webcast and imaging sites you can go to.

For skywatchers in the eastern two-thirds of North American, the Sun rises with Venus already in transit. Venus begins to exit the Sun at approximately 7:05 a.m. EDT (6:05 a.m. CDT). The transit is over by about 7:25 a.m. EDT (6:25 a.m. CDT).

Warning: The Sun is dangerous to look at directly without a safe solar filter. Staring at it can cause serious eye injury or blindness. Fortunately, there are many easy ways to watch the transit safely. If you have keen vision, Venus should appear just large enough to be barely visible as a tiny black dot. But you'll need to use a safe solar filter, such as a #13 or #14 welder's glass or special "eclipse glasses" designed for solar viewing.

Cook And The Transit Of Venus (NASA Science News, May 31, 2004)

Every 120 years or so a dark spot glides across the Sun. Small, inky-black, almost perfectly circular, it's no ordinary sunspot. Not everyone can see it, but some who do get the strangest feeling, of standing, toes curled in the damp sand, on the beach of a South Pacific isle....

Sea gulls fluttered upward, screeching. City odors drifted in from Plymouth, across the ship, shoving aside the salt air. Sails snapped taut. The wind had changed and it was time to go.

On August 12, 1768, His Majesty's Bark Endeavour slipped out of harbor, Lt. James Cook in command, bound for Tahiti. The island had been "discovered" by Europeans only a year before in the South Pacific, a part of Earth so poorly explored mapmakers couldn't agree if there was a giant continent there ... or not. Cook might as well have been going to the Moon or Mars.

He would have to steer across thousands of miles of open ocean, with nothing like GPS or even a good wristwatch to keep time for navigation, to find a speck of land only 20 miles across. On the way, dangerous storms could (and did) materialize without warning. Unknown life forms waited in the ocean waters. Cook fully expected half the crew to perish.

It was worth the risk, he figured, to observe a transit of Venus. [...]

On June 8, 2004, Venus is due to cross the face of the Sun again. The event will be web cast, broadcast, and targeted by innumerable sidewalk telescopes. In other words, you can't miss it. Look into the inky black disk. It can carry you back to a different place and time: Tahiti, 1769, when much of Earth was still a mystery and the eye at the telescope belonged to a great explorer.

The website is here.

Posted by Orrin Judd at June 8, 2004 9:00 AM