Most people don't know that rainbows are actually circles. The reason we normally don't see circular rainbows is because a significant portion of the rainbow is hidden below the horizon.

If you fly in an airplane, you can see a circular rainbow if there is rain in front of you and the sun behind you.

The rainbow has two radiuses / angles of interest.

The primary rainbow has a radius of about 42 degrees from the antisolar point in the center of the circular rainbow.

The secondary rainbow has a radius of about 52 degrees from the antisolar point in the center of the circular rainbow.

If you aren't flying in an airplane, you can only see the part of the circular rainbow that has not disappeared beneath the horizon.

If the sun is low on the horizon, the primary rainbow will be close to 42 degress above the horizon.

If the sun is low on the horizon, the secondary rainbow (double rainbow) will be close to 52 degrees above the horizon.

When the elevation of the sun is more than 42 degrees, you will never see a primary rainbow.

When the elevation of the sun is more than 52 degrees, you will never see a secondary rainbow.

Rainbows are not visible at noon unless you are in a highly elevated position like flying in an airplane.

Rainbows are generally a morning or afternoon phenomenon because of the 42 and 52 degree angles necessary for their visualization.

Low rainbows happen when the sun is higher in the sky.

A rainbow's apex will stand 42 degrees above the horzon only when the sun is sitting on the opposite horizon at sunrise or sunset. When the sun is higher, the rainbow will be correspondingly lower. If the sun is more than 42 degrees above the horizon, the rainbow arc will be entirely below the horizon.

Double rainbows can be hard to understand. How is it that there are two rainbows instead of just one?

Every raindrop is a tiny prism that splits white sunlight into its component colors. The color you see depends on the location of the eye of the observer.

A primary rainbow emits light at an angle of 40 to 42 degrees relative to the antisolar point. When water droplets act as a prism to form a rainbow, the red wavelenghts refract at a 40 degree angle, which is smaller than the angle of the other wavelengths placing it on top of the primary rainbow. The violet wavelength refracts at a 42 degree angle which is why it is at the bottom of a primary rainbow.

A secondary rainbow (double rainbow) has a double internal reflection of light inside the raindrop, and light is emitted at an angle of 50 to 52 degrees relative to the antisolar point. Because of the double internal reflection, the secondary rainbow has inverted colors with violet on the outside and red on the inside of the secondary rainbow arc.

There are millions of tiny raindrop prisms in a secondary rainbow, and the color you see depends on the position / angle of your eye relative to a particular raindrop. A raindrop of higher elevation (52 degrees) will appear violet, and a raindrop of lower elevation (50 degrees) will appear red.

The secondary rainbow is wider than the primary, the colors are more pastel, and they are much less intense / bright because the double reflection inside the raindrop diminishes the amount of light emitted from the raindrop.

In a real sense, nobody sees the same rainbow as you because the angle you are viewing the millions of raindrop prisms is different from everyone else. A rainbow is an intensely personal experience unique to your height and location.

Captain Dave