RAINBOWS why are they a perfect arc?

Question

What makes a rainbow arc shaped?

why do you sometimes see two?

anymore interesting facts that people dont know?

Answer 1

A rainbow forms part of a circle because it is at a definite angle from the line between you and the Sun.  It arises because of dispersion (different angles of diffraction of different colours) in the light bouncing off the back of raindrops.  A double bounce gives you a second rainbow, and one memorable day in northern New Mexico I saw a complete single, double and triple rainbow from one horizon to the other.

Our modern understanding of dispersion goes back to Newton, but the rainbow was explained in large part by Theodoric of Freiburg around 1300, drawing on the experiments in optics by Alhazen (ibn al-Haytham), of Basra some 300 years earlier.

Answer 2

A rainbow is actually a circle, but often not all is visible.

It was Descarte who first published an explanation; the bow is created by the refraction of light through raindrops, which are spherical.

Here is a link to a good page that gives Descarte's full theory.

http://eo.ucar.edu/rainbows/

Answer 3

Because they are the shape of the atmosphere. If people don't know the interesting facts, how can they list them here?

Answer 4

Visible part of a rainbow is a perfect arc because a rainbow is a circle!

Sometimes you see a second rainbow because the sun's light reflects inside a rain drop twice.

some more intersting facts:

Rainbow always appears opposite the sun.

Some people in America think that rainbows are a government conspiracy!

You can never reach the "end" of a rainbow because there is no end, the rainbow is a circle!

Instead of being called a rainbow, it should be called a raincircle.

Answer 5

Actually a rainbow is a circle. I see them as circle when I fly my light aircraft e.g. above the clouds. But since to be seen it requires rain drops and the sun behind you, you see it mostly on the ground when the sun is low over the horizon and then half of the circle is hidden by the ground.

A rainbow is the prismatic reflection of the sunlight on the back surface of water drops. It radiates in a circle of about 40 degrees radius. Sometimes a faint secondary rainbow can also be seen. Often when a dark background like very dark clouds are in the way. The secondary rainbow of a greater radius is simply secondary reflection of the light in the rain drops.