Here’s a great story of someone using their noggin to figure out something about nature. For a long time people have been fascinated by comets passing by the earth. But nobody knew how far away they were. Aristotle, for example, figured that comets were in the upper atmosphere, just a few miles high. Other ancient thinkers thought this was probably wrong. But how could they tell? Can you think of a way? Imagine that you don’t have any modern instruments to use. No hubble telescope, no airplanes, no radar. What might you do? A Danish astronomer named Tycho Brahe figured this one out. In fifteen seventy-seven everyone was talking about a comet that was then in the sky. Since a lot of people had seen it, Brahe travelled around gathering reports.