Eli5: Why is it when standing above a body of water with the sun behind you there is a halo or rays around the shadow of your head?
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There’s lots of tiny spherical drops of water suspended in the air. Any ray of light that hits these water drops will be reflected at a specific angle. Since it’s a sphere, what affects the angle of reflection is where the droplet was relative to the lightray.
Now, there’s an uncountable high number of light rays everywhere hitting the drop from all over, which means the light is reflected in all directions, no matter where the drop is. BUT, for you to see the light, it has to be reflected at just the right angle off the water drop such that the ray bounces into your eye. So, it comes down to where the water drop is relative to your eye, it has to be in just the right place. And this sweetspot is shaped like a cone, which looks like a halo on the other side of your head to the sun, which so happens to be where your head’s shadow is. It’s the same reason rainbows exist, and why they move. No two people see the same rainbow
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