1. The problem statement, all variables and given/known data The Sun sets, fully disappearing over the horizon as you lie on the beach, your eyes 30 cm above the sand. You immediately jump up, your eyes now 170 cm above the sand, and you can again see the top of the Sun. If you count the number of seconds ( = t) until the Sun fully disappears again, you can estimate the radius of the Earth. Use the known radius of the Earth to calculate the time t. 2. Relevant equations 3. The attempt at a solution First, I set up a ratio. change in angle theta/360 = t / 86400 seconds in a day. I solved for the change in the angle theta by using inverse cos (radius of earth/ radius of earth + H, where H is the difference in between standing up and laying down 1.7m-3m). Solving this, I got an angle of .037956 deg. Then the ratio .037956/360 = t/86400, I found t to be 9.1 seconds. This is an incorrect answer, and I was hoping someone point out something I'm missing. I know that when I'm laying down, my view is tangent to the surface of the earth. Advice/diagrams would be much appreciated.