In all of the recent activity surrounding my life, I completely forgot to mention the recent transit of Venus! A transit is when a planet passes directly between Earth and the Sun. Of course, this can happen with only two planets, Mercury and Venus. When the Moon does this it's called a lunar eclipse. Anyway, since Janet brought it up, I'll speak a little more about it. I didn't really watch it for three reasons. One, like Janet said, you'll see it happen again in 2012. Two, it is barely visible to the naked eye. And three, by the time the Sun rose on June 8th, the transit was already in progress in our viewing area. Because of the orbital paths of Earth and Venus, transits occur very predictably four times every 243 years. Once one occurs, another one follows eight years later, then the next 105.5 years later, then eight years after that, then the whole process starts again 121.5 years after that.

The neat thing about the transit of Venus is that it was used to approximate the distance between the Earth and the Sun. A few transits ago, back in the mid 1700's astronomers desperately wanted to know how far we were from the Sun. Of course estimates were made on the fly, but who knew how accurate those were. Finally someone came up with the idea of using the Venus transit to determine this distance. This method of using a transit to determine our distance form the Sun is known as the Parallax Method. It was devised by British astronomer Edmond Halley (yes the comet is named after him) in the 18th century. Basically he said that if you have two people on two widely separated latitude points on Earth, they'll observe Venus passing through the Sun along different paths. By measuring the angular shift between these two paths, our distance from the Sun can be estimated.

Of course, this took a few attempts and a good number of years to get right. Finally on the transit of 1882, William Harkness found the distance to the Sun be 92,797,000 miles. Not too bad considering the Black-Drop Effect (You can see this effect by stretching your arms out and bringing both pointer fingers together in front of a bright light. See how they appear to touch just before they actually do? Imagine how this must have reeked havoc amongst astronomers with such little error allowed). In any event, the average distance from Earth to the Sun is 92,955,850 miles. 150,000 miles is nothing in astronomical terms. Pretty darn impressive if you ask me.

So when the next transit of Venus occurs in 2012, what will the world hold the next transit after that? Where will science have brought us by 2117? Something neat to think about; if humans are on Mars on November 10, 2084, we'll be able to witness our own planet, Earth, move slowly across the Sun in a transit. A mere spec in a sea of light.