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Transit of Venus
Venus will transit the sun on June 5 in North America. This is an extremely rare event that will not happen again for 105 years. (Use proper eye protection when viewing the sun. Please see below.)

What is the transit of Venus?
Approximately every 110 years, the planet Venus crosses in front of the Sun as viewed from Earth. This is similar to a solar eclipse, but with Venus crossing in front of the Sun instead of the Moon.

- NASA's Solar Data Analysis Center. (image) (Modified to show a representation of Venus)
Much more information on the 2012 Transit of Venus is available here and here.

Where and when to see it
The Transit of Venus can be seen in North America, Europe/Asia and the Pacific. In North America, the transit will occur on June 5. Here are the start and end times for a few time zones in the United States. Note that only the northwestern tip of North America will see the whole transit -- it will still be in progress at sunset for the rest of us.
June 5th, 2012 Transit of Venus
Time zoneStartEnd
Central (daylight time)aprx. 5:15pmaprx 9pm (sunset)
Mountain (daylight time)aprx. 4:15pmaprx 9pm (sunset)
Pacific (daylight time)aprx. 3:15pmaprx 9pm (sunset)

More information on the timing of the transit for any location can be found here.
Here is an overview showing where on Earth the transit will be visible (from NASA).

How to view the transit
Always use proper eye protection when viewing the sun. Looking at the sun unprotected can result in permanent eye damage. Solar eclipse viewers are probably the easiest thing to use. I got my hand-held viewers from Rainbow Symphony.
UPDATE: Photo I took of the transit. (Can't see Venus in the photo)