1. The problem statement, all variables and given/known data 2. Relevant equations theta = length / radius 3. The attempt at a solution I came across this question in Fundamentals of Physics (Resnick / Halliday / Walker), in the chapter Measurement. Now I understand that this is a simple geometry-based question. Basically, the '38 min' time period would need to be needed to converted into radians, and then using that relation to find out the length (Earth's radius being a constant). The problem I have is in visualising the situation exactly. I can't figure out what's the significance of 'quickly dims' after the questions says it 'appears 38 min after sunset'. Could someone please explain the arrangement to me?