Tomorrow (June 5) is the transit of Venus. If you have the capability, find a solar viewer (instructions to build one from our friends at CSIRO can be found here), head out a few hours before sunset (in North America), and watch the last transit in your lifetime.
The transit of Venus is when Venus passes directly between the Earth and the sun. This happens (almost always) in pairs–once, then 8 years later, then not for a few generations. The last transit was in 2004; the next will be in 2117.
OK, so a black dot moving across the Sun may not be the most interesting of celestial phenomenon, but it is the rarest of predictable phenomena. According to Wikipedia (I know, I know), the original scientific interest was to determine the distance from the Earth to the Sun:
and from this the size of the Solar System, by employing the parallax method andKepler’s third law. The technique involved making precise observations of the slight difference in the time of either the start or the end of the transit from widely separated points on the Earth’s surface. The distance between the points on the Earth was then used as a baseline to calculate the distance to Venus and the Sun via triangulation.
My plan is to head east with a telescope, a solar filter, and a cooler of beer, and watch something that my great grandchildren will get to see.
If you’re in an area where you can’t see it, or if you have to be inside, you can watch the event here (and other interesting celestial events). You can also find more interesting transit discussion here.
*don’t forget to protect your eyes!