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I was studying the phenomena of the formation of a rainbow. In my book, the following diagram is given:

Rainbow

So, the rays at the red end of the spectrum make a larger angle with the incident ray than the rays at the violet end of the spectrum. However, whenever we see a primary rainbow, the red is always on the top.

Why is it so? I know there is an obvious explanation and I am surely going wrong somewhere in my understanding. Please help me understand my mistake.

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3 Answers 3

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Yes. It is precisely the larger angle that makes this happen. Because the red is angled "down" more the red droplets are the ones located higher in your field of view.

Rainbow

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    $\begingroup$ As they say: "a picture is worth a thousand words". $\endgroup$
    – Diracology
    Aug 6, 2023 at 18:29
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The rainbow is a full circle, of which an observer on the ground only sees part. The digram shows that the red is on the outside of the circle, which, when we see only the upper half of the circle, is the top.

Edit: People keep giving me points. This is embarassing. My answer is wrong (athough the circle comment is correct). The correct answer is the one by @Dale.

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    $\begingroup$ Humility is worth points sometimes! Ha $\endgroup$ Aug 10, 2023 at 18:45
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Think about seeing an object reflected off of a mirror. You can draw a straight line from your eye to the mirror, and then a straight line from the mirror to the object. If you remove the mirror, and want to observe the object as you did before, then you can take the line from the mirror to the object and connect it to the line from your eye to the mirror, and that will tell you where to place the object. In either case, you see the object the same.

Now, for the case case of the water droplets and the sun, imagine the same process but taking into account the dispersion of the water. For the "red object" it will appear "taller" than the "blue" object. Just draw the lines and see where the object shows up.

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