Eli5 : is the order of the colors in a real rainbow always the same? and why , whichever it is?
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Yes, the order is always the same. The refraction that happens in a rainbow isn’t actually “splitting the light into colors,” it’s actually just taking white light (which is a combination of all the visible wavelengths of light) and spreading them out like an accordian. So, the colors you see will be ordered by the wavelengths of light.
Low frequency light wavelengths that we can see start at red and as the frequency increases you get up into orange, yellow, green, blue, etc.
Yes, always. Because the frequency of the light is what determines what color it is, and it’s the light that’s getting separated into its component wavelengths. Each wavelengths “bends” a little more than the one before it (gets diffracted)
Yes the order is always the same.
A light’s colour is determined by its wavelength. “White” light, like sunlight, is a combination of all the different colours.
Rainbows happen when the suspended drops of water in the air act like prisms and refract the light. **When light goes through a prism, it gets bent by an amount that depends on its wavelength**. The longer the wavelength the less it is bent, the shorter the wavelength the more it is bent. [That means the light gets “fanned out” according to colour](https://www.sciencefacts.net/wp-content/uploads/2020/05/Prism.jpg). Red has the longest wavelength and gets bent the least, orange gets bent a little more, etc etc.
The brightest rainbow always has the same colour order, with red on the outside, but in ideal conditions a secondary rainbow can become visible outside the primary. The colour order of the secondary rainbow has the red on the inside, the opposite to that of the primary.
The reason for the difference is that the secondary rainbow involves the light being bent through more than 180°, i.e., it’s bent back on itself.
Violet has the shortest wavelength, so the greatest chance to interact with a more dense medium. This slows it more than blue, which is more than green… you get the idea.
Hitting straight on you wouldn’t notice, but at an angle, it causes the light to bend (think of driving a car, then slowing the left wheels more than the right, the car will turn).
Because the Violet portion bends the most, it ends up on one end, and the red (which bends the least) ends up on the other.
Sort of, the Rainbow is actually a series of concentrical circles. The reason it’s a bow is that the horizon usually cuts off the other half and the additional bows are fainter and thus less likely to be seen. The order of the colors reverse for the secondary rainbows.
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