Try it on paper first. A hint, the key idea and the worked solution are here when you need them.
A student wants to make a rainbow with a garden hose on a sunny afternoon, when the Sun is high. Where should she stand, which way should she spray, and how high above the horizon should she look for the top of the red bow?
In each raindrop sunlight is refracted, reflected once at the back, and refracted again. Red comes back at about from the point opposite the Sun, violet at about , so red is on the outside. The point opposite the Sun is as far below the horizon as the Sun is above it. A fainter second bow, at about , has two reflections and its colours reversed.
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. Where to stand. With her back to the Sun, spraying a fine mist in front of her.
Step 2. Why. Each drop refracts, reflects once at its back, and refracts again, sending the colours back toward the side the Sun shines from.
Step 3. Where to look. The top of the red bow is above the horizon: low, near the spray.
Answer: back to the Sun, spray in front, and look about up.
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