The Size of the Sun Seems like an easy thing to observe. However, it is not. The problem is that one must use filters and that changes the light from the source. Solar eclipses provide a great way to measure these values to a very precise level and even today, progress is being made along those lines by attempting to simulate the timings in advance.

(c) Eclipse Nuts Cartoon by Bill Kramer. Uploaded Sun, 02 Apr 17 08:38:37 -0400