During the summers at high latitudes, ghostly, silver-blue cluds occasionally appear after sunset when common clouds are in the Earth's shadow and no longer visible. These are called mesospheric clouds.
If mesosspheric clouds are spotted 38 minute after sunset and then quickly dim, what is their altitude if they're directly over the observer?
theta = length / radius
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?