Updated 06/05/12 - 8:39 p.m.
CHICAGO (CBS) -- Hundreds of millions of people across the Earth found their eyes focused on another planet on Tuesday, as Venus passed directly in front of the Sun.
NASA provided live video of the Transit of Venus, which appeared as a small dark spot moving slowly across the face of the Sun.
For seven hours, earthlings could see Venus as it crossed between the sun and our planet. Adler astronomer Mark Hammergren said, using a telescope with the proper filtering protection, skywatchers could see the planet Venus as a black dot passing over the Sun for nearly seven hours.
It started shortly after 5 p.m., and was expected to last until about 10 minutes until midnight.
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CBS 2's Mike Parker watched it unfold, along with many others at the Adler Planetarium.
Thousands of people showed up to see the show outside the Adler. No car crashes or explosions, no profanity; just the magic of the movement of the Solar System.
Experts emphasize that skywatchers mustn't look directly at the Sun to see the event. Instead, they should use special protected telescopes.
The effect was astronomical. Among the witnesses was a group of astronomy students from the University of Chicago.
"I study planets, so it is my bread and butter, but I'm just really enthused at how many people find this as cool as I find it," Alissa Bans said.
In addition to those wearing special glasses provided by the Planetarium, there were long lines of people who waited more than an hour to get their turn peering through dozens of solar telescopes, to watch the slow movement of Venus as it passed in front of the Sun.
With one of those telescopes, watchers could also see the solar flares around the corona of the Sun.
Many of the scopes were brought by enthusiasts from the Chicago Astronomical Society. Others were provided by Adler volunteers, like John Napolitano.
"The skies are free and we're happy to share it," he said.
Planet watcher Dan Herbst said, "It just puts things in perspective to know that that little dot is a planet, and we're just another planet."
Planetarium astronomer Dr. Mark Hammergren said, "I think that's really the key thing for today's Transit of Venus, that people should take away from it. It gives us a wider view of the universe, than just our own backyard."
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."
Explorers discovered new lands by traveling the globe to view the transit of Venus. British explorer Captain James Cook, for example, traveled to the south Pacific to watch the transit of Venus from Tahiti. Cook created maps of large sections of the globe.
"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 told CBS 2's Kris Gutierrez and Roseanne Tellez Tuesday morning.
Seeing it directly through a telescope was a unique experience. It wasn't a picture somebody sent you on their iPhone, it wasn't a TV image, it was actually the Sun, and it was actually Venus – at that moment.
It wasn't reality TV. It was reality. And it won't happen again until 2117.
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