Observatories the world over will be watching on Tuesday as Venus crosses the face of the sun for the last time in any of our lifetimes. It will be a banner day for astronomers, providing ample opportunities for measuring Venus' characteristics, and for determining some rules that will help in the hunt for exoplanets. But it's also just an amazing thing to behold, and you can watch it, too — as long as you follow some safety precautions.
First and foremost: Never look at the sun directly. Your retina does not have pain receptors, so you'll never feel it as the sun's blazing glare fries your eyes.
Astronomy clubs, universities and planetaria around the country will have special glasses you can wear — and you can go here to find one in your area. If you saved the eclipse glasses you wore for the solar eclipse last month, those will work, too. If all else fails and you just have to see it with your own eyes, go to a hardware store and buy #14 welder's glass. That's the only glass dark enough to protect your eyes.
Sky & Telescope magazine has an excellent go-to guide, where you can learn more about how to safely observe the sun. The entire United States will be able to see at least part of it.
If it's cloudy, plenty of observatories are planning live webcasts through various solar telescopes. NASA will be webcasting from the summit of Mauna Kea in Hawaii. The island state will be able to witness the entire transit, while much of the rest of the country will see only part of it before the sun sets.
The Exploratorium in San Francisco will be webcasting from the Mauna Loa Observatory.
Astronomers Without Borders will be webcasting from Mount Wilson Observatory in California.
The University of Barcelona will webcast from Svalbard, Norway, where the transit will be visible at sunrise. (Site is in Spanish.)
is there a reason why we wont see it again?
is venus flying out of its orbit?
is eaths orbit not in sync with venus?
why did it take only 8 years for the transit to happen again
and now a century for the next one?
will there be a next one?
The reason we won't be able to see it again until 2117 is because Venus is on a different orbital plane than the Earth. Therefore, it is rare (in human terms) for Earth and Venus to be aligned properly for a transit to occur.
Here's an excerpt from Wikipedia:
"Venus, with an orbit inclined by 3.4° relative to the Earth's, usually appears to pass under (or over) the Sun in the sky at inferior conjunction. A transit occurs when Venus reaches conjunction with the Sun at or near one of its nodes—the longitude where Venus passes through the Earth's orbital plane (the ecliptic). Although the inclination between these two orbital planes is only 3.4°, Venus can be as far as 9.6° from the Sun when viewed from the Earth at inferior conjunction. Since the angular diameter of the Sun is about half a degree, Venus may appear to pass above or below the Sun by more than 18 solar diameters during an ordinary conjunction.