Filters, Or n1 / sin (θ1) = n2 / sin(θ2)
Rainbows do not actually exist, but are optical illusions dependent entirely on an observer's relative position to light and water.
For example. An observer is standing on a ship at sea; the source of light is the setting sun and the water is the last of a sudden storm that the ship is passing through.
The observer is not alone, but surrounded by relatives at a reunion who have all gathered for a photograph (another creature of optics and illusion) in front of a large picture window overlooking the prow of the ship. The photo is taken, the groups turns, the rainbow appears.
A rainbow is the result of light undergoing total internal reflection in myriad water droplets.
Everyone smiles, and one observer voices the single thought of the group – a woman's name, a pronouncement of presence signified by a beautiful thing that does not really exist, but that everyone gathered in that particular, that singular place out at sea nonetheless can observe.
In other words, it all depends on where you stand, and where you look.
“You should have seen it. Everybody just smiled and someone said, “There's Liz. And it was.”
Once upon a time, a ship passed through a storm at sunset and a rainbow appeared. A common sight.
Once upon a time, a family gathered for a photograph at a reunion arranged by a woman who died two years previously. Just after the photo was taken, a rainbow appeared, and everyone knew she was there.
Once upon a time, a food Nazi took her boyos to the grocery store and in a moment of indulgence, let one of them grab a box of rainbow fish crackers. Instead of putting it in the cupboard, she stared at the box on the counter for a couple of days, never realizing it was a punchline.
(The first part of this story is here.)