This photograph was taken in 1882. It shows Venus during the transit of 1882. The big white circle is the Sun. Venus is the black dot on the Sun. Venus is near the top of the Sun, just left of center. Click on image for full size (19K JPEG) Image courtesy the U.S. Naval Observatory Library.

Sometimes Venus passes between Earth and the Sun. This event is called a transit of Venus. Transits of Venus don't happen very often. There is a pattern in the time between transits of Venus. The pattern goes like this: after one transit there is another one eight years later, then more than 100 years go by, then another transit and then another eight years after that, then another wait of over 100 years, and so on.

The last Venus transit was in 1882. There are two coming up soon, on June 8, 2004 and June 6, 2012. After that there will be a long wait until the next transits. The next ones after 2012 will be on December 11, 2117 and December 8, 2125

There have only been six Venus transits so far since people started using telescopes to look at the sky. Those six were in the years 1631, 1639, 1761, 1769, 1874, and 1882.

A couple hundred years ago people didn't really know how far the Earth is from the Sun or how big our Solar System is. Astronomers were able to find out those distances by making measurements during Venus transits. They had to make measurements from many different places on Earth. During the Venus transits in the 1700s and 1800s, scientists made those measurements from many places on Earth. They were able to figure out that Earth is about 150 million kilometers (93 million miles) from the Sun.