So I know that rainbows happen when sunlight gets bent and spread out by raindrops, kind of like how a prism works.
And I get that a rainbow is something I see based on where I am and where the sun is shining from behind me.
What puzzles me is this: since those raindrops (acting like little lenses) are always falling and moving around, why doesn’t the rainbow flicker, shift, or vanish?
Especially during light rain when there aren’t that many raindrops to begin with. It’s hard for me to imagine that as one raindrop falls out of place, another one perfectly replaces it immediately.
How does the rainbow stay so stable and clear to me under these conditions?
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The same reason why if you squint your eyes, static can look like a grey blob. The drops are so small and so far that their movement is just interpreted as “fuzziness” by your brain.
> It’s hard for me to imagine that as one raindrop falls out of place, another one perfectly replaces it immediately.
You’re right. That doesn’t happen. What does happen, though, is somewhere in the vague vicinity of the raindrop that just moved out of the sweet spot is another droplet moving into it, and since the rainbow is so far away and the raindrops are so small, the slight difference in displacement isn’t discernible to you. It all just blurs together.
Also, keep in mind that rainbows appear 2D, but they’re caused by particles falling in 3D. Two droplets don’t need to be physically close together for one to “take the place” of the other. You have that whole third dimension for drops to fall in front of or behind one another, too. To your eyes, at that distance, it all looks flat even though it isn’t.
If you instead made a rainbow yourself using the mist setting on a garden hose spray attachment, you actually would see the rainbow flicker the way you expect.
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