At sunset the Sun looks flattened, wider than it is tall. Explain. Why does it look round at noon?
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
At sunset the Sun looks flattened, wider than it is tall. Explain. Why does it look round at noon?
Need a reminder? The key ideaShow
The air is denser near the ground, so starlight bends as it comes down. Stars look higher, and they twinkle as the air moves. The Sun is seen about before true sunrise and after true sunset.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. The lower edge. Its light crosses more air, low down, and is bent more, so it is lifted more.
Step 2. The upper edge. It is lifted a little less. So the disc's height shrinks, but its width does not.
Step 3. At noon. The light crosses little air almost straight down, so the lift is tiny and the same for both edges: the Sun looks round.
Answer: the lower edge is lifted more than the upper one near the horizon; at noon the bending is too small to show.
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