Note: this is not a H.W. problem. I'm just curious about it. Imagine you are a flatlander living on a spherical planet. If you don't have any suns or any other satellites to work with how would you go about finding out what the radius of the planet is? I don't think i know enough spherical trig. to give a good answer. Would there be a way to trek out a triangle and measuer the angles and then tell from the excess of the angles?