Parallax Project

In the late 17th century, Giovanni Cassini used the parallax technique to measure the distance to Mars. Cassini knew that a larger parallax would be easier to measure - but this required a larger baseline (ie, the baseline would be like the distance between your eyes). He took measurements of the position of Mars from Paris and sent a fellow astronomer to French Guiana in South America to do the same. This gave him a baseline of several thousand kilometers - using geometry, he was able to calculate a distance for Mars that is only 7% off today's more precise measurements! (Try this page for the mathematics for the calculation.)