Tampa, Florida -- A group of planetary enthusiasts gathered to watch the transit of Venus take place tonight on the roof of the IMAX dome.

The transit officially started at 6:09 p.m. and will last almost seven hours.

Photo Gallery: Transit of Venus
See Also: Solar halo, sun dogs spotted!

For self-professed astronomy lovers like MOSI's Timothy Hill, the transit of Venus is about as cool as it gets.

"To have people be able to look up at it and kind of understand how the solar system and how the solar system works, that's pretty phenomenal. So yeah, it is very exciting," said Hill.

Hill was leading a group of transit observers atop MOSI's IMAX Dome theatre. Using a special solar scope, they planned to witness the celestial phenomenon.

It's unsafe to stare at with naked eye. Do-it-yourself observers need special glasses with at least a number 14 rating.

"And beware of the knock-offs which are usually shade 5 to shade 10. You don't really want to look at the sun through those," warned Hill, "You're really looking for shade 14 or things that specifically say eclipse glasses or eclipse goggles."

Since Earth is the third planet, we can only see Mercury and Venus pass between ourselves and the Sun.

But unlike Mercury, Venus's transit is visible to the naked eye, and it's far more rare, occurring in pairs about every 100+ years.

The next Venus transit won't be visible until the year 2117.

That planetary perspective was not lost on visitors.

"When you get to actually see something like that for once in a lifetime, it's a good chance to think about something outside our planet," said Keith Enfinger.

Liz Smith-Incer, also visiting MOSI agreed.

"We're learning to become stewards of the planet Earth and we're probably not the only planet in the universe," she saud, "So, I think it's important that we appreciate what's going on in other parts of the universe."