NIGHT SCHOOL

Newton asked it with a cannon: if you fire a ball from a high enough mountain, it falls to the ground. Fire it faster, it falls farther. And if you fire it fast enough — it falls all the way around. The three boards below draw themselves; read them left to right.

So the moon is falling — it has been falling for four and a half billion years, and it keeps missing. Orbit is just falling with enough sideways. That one sentence is tonight's entire lecture; everything else is arithmetic.