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We have contact! For the last time in 105 years, Earthlings and astronauts are watching the planet Venus creep across the surface of the sun during a scientifically significant transit that lasts almost seven hours.
The prime viewing zone takes in most of the America and the Pacific and Asia. Millions all over the world, like myself was watching through NASA and more than a dozen other webcasts. Pictures and videos are streaming in, from around the globe as well as from the orbiting International Space Station.

Only seven Venus transits have been witnessed since the invention of the telescope 400 years ago. Venus comes between Earth and the sun five times in the course of every eight years, but because of the inclination of the planets' orbits, Venus usually misses passing over the sun's disk, as seen from Earth. In fact, that passing-over phenomenon occurs only twice in the typical person's lifetime. Two transits occur eight years apart, but each pair is separated by either 105.5 years or 121.5 years. We had a Venus transit in 2004, and we're having another one today. The next one won't come until 2117. So if you're into rare sky phenomena, today is as good as it gets.

Venus' disk begins to pass over the left edge of the sun's disk a little after 6 p.m. ET, and makes a stately crossing that lasts until about 12:50 a.m. ET. Some part of the transit will be visible from most locations on Earth — though you're out of luck if you're in eastern South America, western Africa, the Iberian Peninsula, Antarctica or the middle of the Atlantic. It took Venus 6 hours and 40 minutes to travel across the Sun's disk. Seen from the Earth's center (geocentric coordinates), the transit started at 22:09:29 and ended at 04:49:27 Universal Time (UT).

Scientifically speaking, the most important moments come as Venus crosses the edge of the sun's disk. That's when the sunlight refracted by Venus' atmosphere can be most easily detected — revealing the atmosphere's chemical signature. Astronomers eventually hope to use a similar technique to analyze the atmosphere of planets passing across alien suns, so this transit provides a good practice run for the technique. Even the Hubble Space Telescope is trying out the method, by checking the characteristics of the sunlight reflected by the moon during the transit.

Sometimes its just spectacular to have the world pause, look up into the skies and witness a universal event take place. Suddenly the world is just that much smaller.

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