system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5. Why do rainbows all have the same shape. You never see one going straight overhead or see one from the end.
gpt
Because when a raindrop bends light, the light exits the raindrop at an angle 40 to 42 degrees away from the angle it entered the raindrop.

If the sun is very low in the sky, either just before sunset or just after sunrise, we can see a half circle.