Seeing the transit of Venus is a twice-in-a-lifetime opportunity. The planet passes in front of the Sun on two occasions eight years apart — and then not again for about a century. There was a transit in 2004 and another one will occur tonight. If you miss that, you'll have to wait until 2117 to see it again.
For centuries scientists have traveled across the world to get the best vantage point for a transit of Venus. Even today, astronomers and space-lovers use the transit of Venus to take measurements and learn more about our solar system. Miles O'Brien, science correspondent for PBS NewsHour, has covered space issues for over 20 years.