Why are rainbows elliptical?

Question

What I'm trying to ask is: Why a half circle instead of a straight line or a wide field of color?

Answer 1

Disclaimer: This is really hard to get across without a picture...

Rainbows come from sunlight bending through water droplets at a very specific angle (23.5 degrees)...

The sun shines from one point in the sky and your eyes are at one point on the ground. These two points (the sun and your eyes) form two points of a triangle. The third point (which is where you measure the angle of reflection) is where the rainbow is.

If you draw a series of points in a straight line across the sky, the angle formed by your eyes and the sun at every one of those points will be different! Now, instead, if you find every point of intersection in the sky where lines drawn from the sun and your eyes make a 23.5 degree angle, you'll end up with the shape of a circle... it's only half of a circle or less because the center of this circle would be below the horizon (if you draw a straight line from the sun through the point where your eyes are looking from, it will point down through the earth... so you can only see the part of the circle that is above the horizon. If the sun was shining from below the horizon behind you, you'd be able to make a full circle)

One more way to visualize this is to imagine that you're standing exactly in the center of a huge cylindrical can. If you look anywhere along the bottom of the cylinder, the angle at which you're looking downward is exactly the same all along the bottom of the cylinder. If you were standing in a square room, the angles would change as you followed the bottom edge of the wall from the center towards the corner of the room. This is why rainbows are NOT square.

Answer 2

Rainbows are circles, but if you are on the ground you only see half of them.

If you are in an airplane, it is possible to see the entire circle.

They are circles because the source of illumination is nearly a point (the sun) and because of the angle that light refracts through raindrops. The red part of the rainbow is at exactly 42 degrees from the opposite position of the sun.

A fixed distance from any point will always give a circle (or an arc).

Answer 3

Actually, it is a *full* circle - but you can't see the other half.

The centers of all those circles is the source of the light which creates the rainbow. The light gets broken down into light of different wavelengths - and the distance from the source to each circle is proportional to the wavelength of the light.

Rainbows actually have more than seven colors (ROY G BIV) but the other colors are not in the visible spectrum....

Answer 4

They're actually circular, but from the ground you can only see part of it. If you're high in a plane & manage to see a rainbow on the clouds beneath you, you will see the entire circle and not just a part of the arc. The angle is constant, and you have to be very, very far away from it for the entire circle to be visible from your vantage point - and then, the earth, itself, can't be in your way. ;-)

Answer 5

The various colors are seen at an angle 40.6 degrees to 42 degrees relative to the incident light. Explanation with diagram at the reference.

Answer 6

If they were straight they wouldn't be called rainbows. What do you mean by "wide field of color"?

Answer 7

the wave length of red light is longer than that of violet light
hold a long flexible stick next to a shorter flexible stick and place the ends together - the only way to do it is to bend the longer stick into an arc right?

Answer 8

They are called "sun dogs" if they are in a wide field of color. I have only seen that twice in my lifetime but it was beautiful.

Answer 9

It is due to constant angle between light source and observer. The angle is always maintained.
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KrazyKyngeKorny(Krazy, not stupid)
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