Furthermore, if the flat earthers counter by suggesting that the moon and sun are very close to one another but not on a direct collision course, fire radio waves at both the moon and sun, and note that only the moon is reflecting the radio waves back in any measureable manner. Note also that the time it took for the radio waves to go to the moon and back does not correspond with what we'd expect if the measurements we have supported flat earth theory, proving we have the earth's radius, not the sun/moon distance.