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Jun 05 2012

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Did You See? Venus Makes Last in a Lifetime Transit Across Sun

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LIVE VIDEO — Watch NASA TV’s live coverage of the Venus transit. This picture, captured by NASA’s Solar Dynamics Observatory, shows the planet just as it was crossing the edge of the sun’s disk.

By Alan Boyle

We have contact! For the last time in 105 years, Earthlings 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 Americas, the Pacific and Asia, as shown on the map below. But even if you’re not in the transit zone itself, you can get in on the action over the Internet, thanks to NASA and more than a dozen other webcasters around the globe. Pictures are streaming in:

NASA via Reuters

An extreme ultraviolet picture of the sun from NASA’s Solar Dynamics Observatory shows the planet Venus in transit, as well as dramatic swirls of solar activity.

Stan Honda / AFP – Getty Images

Venus can be seen at top right, beginning to cross the face of the sun, in a picture of the transit taken from Manhattan’s West Side.

Andrew Burton / Getty Images

New Yorkers observe the last-in-a-lifetime transit of Venus from the High Line park.

NASA / SDO via Reuters

The planet Venus begins its six-hour-plus journey across the face of the sun, as seen in a close-up from NASA’s Solar Dynamics Observatory.

Stan Honda / AFP – Getty Images

Clouds partially obscure the sun during the transit of Venus, as seen from Riverside Park on Manhattan’s West Side.

The first scientific observation of a Venus transit took place in 1639, and there have five other transits to watch between then and now. 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 this is the second event in the pair. The next transit won’t be seen until the year 2117 — thus, this is the last event of its kind that anyone alive today is likely to see.

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.

If you want to see the transit yourself, make sure you do it safely — either by using appropriate protective eyewear or indirect observation methods such as a pinhole camera. There may be special events planned today by your local astronomy club, science center or observatory. Do not gaze at the sun without proper protection. Sunglasses won’t do the trick, no matter how many you pile onto your face. Get the details from this safety guide.

The safest and surest way to see the transit is on the Web. So check out this list of webcasts, and check back for updates as the transit continues.

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