Because certain factors have to line up, transits of Venus are relatively rare. Venus, which is closer to the Sun than our planet, must move between the Earth and the Sun. Such conditions occur in pairs eight years apart, which are then separated by about a century between the next pairing. For example, there were transits of Venus in 2004 and 2012. The next pair will be in December 2117 and 2125.
This phenomenon is about more than simple viewing pleasure for curiosity seekers. It has yielded important information to astronomers for centuries. The transit of Venus originally gave scientists clues about the size of our solar system. In more modern times, astronomers use what’s known as the transit method to detect planets orbiting other stars; they can detect tiny blips moving in front of stars, resulting in a very slight dimming and indicating the presence of a planet.
If you’re feeling down in the dumps about the long wait, you still have the opportunity to catch the transit of Mercury in 2016.
