To watch the "Transit of Venus" click the link below
http://www.cbsnews.com/video/watch/?id=1n&tag=watchnow
CBS News — A rare astronomical event will happen late Tuesday afternoon, and chances are you won't see it again in your lifetime if you miss it.
The event is called the Transit of Venus. The planet Venus will pass directly between the earth and the sun.
"This is only the seventh Transit of Venus that has ever been seen, and because we needed the telescope to be able to actually see Venus properly; see the sun properly, and so this wasn't even known until the 1630s," master educator Michelle Nichols of the Adler Planetarium said.
Adler astronomer Mark Hammergren says it will be 105 years before the next transit of Venus. Using a telescope with the proper filtering protection, the event features the planet Venus passing in front of the sun.
"You would see a tiny, tiny black dot tracking across the face of the sun, very slowly over the course of a few hours," Hammergren said.
So why is this such a big deal? Early astronomers used the Transit of Venus to determine the size of the solar system.
"Astronomers really didn't have a good fix on the absolute size of the solar system and the spacing of the planets," Hammergren said. "The only way to gauge that absolute size and get a full sense of the size of the solar system was to view this transit of Venus."
If you're planning to view the Transit of Venus yourself, experts emphasize that you not look directly at the sun.
"Never look directly at the sun, so not even sunglasses will help you with this one," Nichols said.
But using the protected telescopes, you'll be in for a sight.
