Johannes Kepler had the relative sizes of the orbits of our planets in the solar system mapped by the 1630s. The shape of the solar system had been known relatively well, but it was a shape without scale. Determining the size of the solar system was a much more challenging problem, mainly because there was no known way to make such a measurement. However, that all changed with the development of parallax and taking advantage of an even more fascinating phenomenon: the transit of Venus.