…If you’ll be willing to bear with me here, long enough to see if my grip on optics, meteorology, or biology is more appalling.
Anyway, say there was blood raining from the sky—with the right quantity and whatnot and with the right light conditions to form a rainbow.* Would the colors of said rainbow differ, noticeably, from those seen in a normal rainbow?
Like I said, I have several intersecting gaps in my area of knowledge in regards to this particular question, and it’s not something that I really have the time to figure out via experiment.
Can anyone help me out?
*That’s assuming, right off the bat, that that blood is not sufficiently different in physical properties from rainwater to do so.
If you had “raindrops” of some other material than plain water, it would certainly affect the appearance of the rainbow.
First, if the liquid were some other substance than pure water, the refractive index would change, and that would affect the angular position of the rainbow, and possibly also the dispersion (the way the different colors fan out). Even plain water with sugar or salt in it has a slightly different refractive index (although not by a lot), and blood has both.
Second, if the drops are colored, that indicates that there is absorption of differemnt wavelengths. Red drops would more absorption at the short wavelength end of the scale, among the blues and greens, and so you’d expect the resulting rainbow to be deficient in the short wavelengthn side of the scale.
You actually do get an effect like that now, when you have a rainbow formed by ordinary water raindrops, but with the light from a red setting sun. I’ve seen these – they’re all yellow, orange, and red.
But if you actually did have drops of blood in the sky, suspended so as to form a rainbow, I strongly suspect you wouldn’t see anything. Rainbows form from light that enters a drop, reflects once or twice from the interior surface via Fresnel reflection, then refracts again as it exits. You need a transparent drop. Blood isn’t very transparent. The red blood cells will scatter the light catastrophically, and you won’t get the sort of clean, directed light you need to form a clear, sharp, rainbow.