Some questions about rainbows.

The rainbow’s position is entirely determined by where the sun is relative to your head. If you were to draw a line from the sun extending through your head, that line would continue on past your head and point to the center of the arc of the rainbow. The colored bands will then appear along the arc that lies about 40 degrees off that center point.

The bands of color are reflected from droplets of water, not molecules. The rainbow is the cumulative result of seeing a reflection of the sun from the backside of billions of individual water drops. Those drops are not at all in the same plane, so the rainbow doesn’t lie at any defined distance from you. Some of the reflecting droplets may be just a few feet away from you, others may be miles away. If a ray that is coming at your eye from a far away drop gets intercepted by another drop along the way, it will simply be bent off in a different direction and you’ll never see it.

I meant to say water droplets. I just got out of cells and molecules and we were talking about water lol

@thorninmud described it beautifully. But i will add one thing. You can always tell where the rainbow ill be in the sky. Stand with the sun behind you and look at shadow you head makes on the ground. Now extend you arm and make a fist. Your fist is typically 10 degrees. Put your fist on the center of the shadow your head makes and count off 4.5 fist widths. Rotate it around the shadow. There’s your rainbow.

If it is not there, don’t bother looking . It won’t be anywhere else.

BTW, here’s another Q where we hashed out the physics of rainbows pretty thoroughly

Why is there the flatish bit at the top?

Not sure what you mean. As far as the rainbow is concerned, there isn’t really a “top”. The rainbow would be a perfect circle if the horizon didn’t cut it off at the bottom. I can’t see any flat in this image, for example.

there is not a flat part at the top, it is a perfect circle with the bottom part below the horizon. the part that looks flatter is an optical illusion due to the curvature of the earth. I do have some wonderful pictures of complete circle rainbows, but you have to be in a plain to see them.

Look here

and here

Rainbows aren’t actually bows. They’re rings. Halos, actually. Like the halo of light around a candle’s flame. It’s just that you can’t really see the bottom half.
That’s why they’re bent like that and always seem perpendicular to you.

Oh, looks like @thorninmud and @DrBill beat me to it.

(As a side note, this sort of misinterpretation is why I think it would be a good idea to call them something more accurate, like rainhalos or prismatic halos.)
(All in favour, say aye.)

I didnt mean perfectly flat I just mean it levels out more at the top. But you guys already explained it better. I’d love to see some images of a fully circular rainbow. Would that be possible from a plane or something? How high would you have to be?

@DrBill just posted two. :)
There’s also this one here.

As for how much altitude it takes, I don’t know. This one was taken while skydiving, but that first one by @DrBill was up in the sky and could be seen from the ground. I suppose it depends on the angle from which the halo is shining at you.

Can’t really use the word “halo” to apply to rainbows because it’s already used to refer to a different phenomenon, the one in @DrBill ‘s 1st picture. These appear around the sun or moon, and are caused by the refraction of atmospheric ice crystals. Rainbows are always seen when the sun is at your back.

@thorninmud
Ah? Well shoot.
Do you know of some other term we could use instead, maybe?

Rainbows are an optical illusion created by a combination of refraction and reflection from small water droplets in a particular range of sizes. All of the properties – the angular size, the sequence of colors, the darkening outside the bow, the presence of secondary and supernumerary bows – can be analyzed based on simple optics.

I learned this from a Scientific American article that I read MANY years ago. Some of this is explained in the Wikipedia article…

The light is first refracted entering the surface of the raindrop, reflected off the back of the drop, and again refracted as it leaves the drop. The overall effect is that the incoming light is reflected back over a wide range of angles, with the most intense light at an angle of 40–42°. The angle is independent of the size of the drop, but does depend on its refractive index…

Btw, @DrBill‘s second link shows not a rainbow but what’s known as a glory.

Why do we see different colors? Do different frequencies have different refractive indices?

Different frequencies are refracted a different amount. Hence the colors seen through a prism, as first described by Mr. Newton. That’s called dispersion. In effect the index of refraction varies with wavelength.

pics posted after I asked lol but thanks guys. I saw a sun dog or glory when I was in Honduras but thought that was different than a normal rainbow so I didnt mention that above. saw a moon dog too which was pretty cool. like a grey washed rainbow