June 5, 2012 at 6:06 PM ET
For the last time in 105 years, Earthlings and astronauts watched the planet Venus creep across the surface of the sun during a nearly seven-hour transit.
The prime viewing zone took in most of the Americas, the Pacific and Asia. But even if you weren't in the transit zone itself, or even if the weather was lousy (as it was for me in the Seattle area), you could get in on the action over the Internet, thanks to NASA and more than a dozen other webcasters. Pictures and videos were streaming in, from around the globe as well as from the orbiting International Space Station. Here's a sampling:
The first scientific observation of a Venus transit took place in 1639, and there have been six other transits since then. Because of the orbital mechanics of our solar system, Venus can be seen crossing the sun's disk from Earth in pairs of occurrences separated by eight years. There are gaps of either 105.5 or 121.5 years between one pair and the next. One transit took place in 2004, and today's crossing was the second transit of the pair. The next transit won't be seen until the year 2117 — thus, this was the last event of its kind that anyone alive today is likely to see.
Scientifically speaking, the most important moments came when Venus crossed the edge of the sun's disk. That's when the sunlight refracted by Venus' atmosphere could be most easily detected, revealing the atmosphere's chemical signature. Astronomers eventually hope to use a similar technique to analyze the atmosphere of Earthlike planets passing across alien suns, so this transit provided a good practice run for the technique. Even the Hubble Space Telescope tried out the method, checking the characteristics of the sunlight reflected by the moon during the transit. We'll be hearing more about the results of those experiments in the weeks ahead.
But there's more than science involved here: Sue Ah Chim, a researcher at the Korea Astronomy and Space Science Institute in South Korea, told The Associated Press that he hoped the transit would lead people to see life from a larger perspective and "not get caught up in their small, everyday problems."
"When you think about it from the context of the universe, 105 years is a very short period of time, and the earth is only a small, pale blue spot," he said.
At Los Angeles' Griffith Observatory, Jamie Jetton and her two nephews from Arizona, aged 6 and 11, sported sun-viewing glasses as the followed the transit. "It's an experience," she told AP. "It's something we'll talk about for the rest of our lives."
More about the transit:
More places for pictures:
Update for 11:35 a.m. ET: I initially wrote that Pettit's groundbreaking pictures were "the first pictures of a transit of Venus taken from outer space," but Facebook friend Jarin Udom pointed out that several sun-watching probes, including NASA's mighty Solar Dynamics Observatory, have taken plenty of such pictures previously. So it's more accurate to say these were the first pictures taken by a photographer in outer space.
Got pictures? Use the FirstPerson photo upload tool to share your transit photos with us. They may show up in a gallery today or on Wednesday.
Last updated 1:45 a.m. ET June 6.
Alan Boyle is msnbc.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.