Hold a small coin to eclipse full moon. Measure the angle it subtends, estimate the diameter of moon.?

Question

Here's the question in full: hold up a small coin to so that just eclipses the full moon, measure the angle it subtends at the eye. From this result and the distance from moon to Earth (3.8 x 10^5 km) estimate diameter of the moon.

You don't have to give me the answer, but I really have no idea where to head, so if you could point in the right direction.

Answer 1

In the case of the moon we have: angle in radians=Diameter moon/Distance moon. In the case of the coin we have: angle in radians=Diameter coin/Distance coin.

As both angles are made equal we have:

Diameter moon/Distance moon = Diameter coin/Distance coin. The only unknown in this equation is the Diameter of the Moon.