This chapter tries presents the evidence for the statement that the earth goes round the sun once a year in an orbit nearly two hundred million miles across. The orbits are not exactly ellipses, because the planets are attracted by one another according to Newton's laws as well as by the sun. Einstein's modification of Newton's laws embodies a much smaller correction. Still the apparent motions would be just the same, though no simple theory could explain why they occurred, if the earth were still, the sun moved round it, while the other planets moved round the sun. In the next few years it is probable to know these distances much more accurately by radar. Echoes from the moon have already been picked up, and it should be quite possible to measure the distance of the nearest part of its surface within a few miles.