A rainbow is formed due to refraction then total internal reflection and again refraction of sunlight, when it passes through the raindrops.
The sunlight refracts (bends) as it passes through the raindrops. The bending of the sunlight causes the colors to split according to their wavelength. Then, the split colors strike the inner surface of the water drop to form a total internal reflection. At last, while leaving the raindrops the spectrum of seven colors refracts again to form a rainbow.

A double rainbow is formed when two refractions and two internal reflections of sunlight take place.
In a double rainbow, the primary rainbow becomes the inner one with a darker color and will have a (ROY G BIN) pattern. The secondary rainbow appears outsides the primary rainbow with a lighter color and the pattern is reversed (VIB G YOR).

There are seven colors in the rainbow.

The primary rainbow is most commonly seen.
They have red as the outer edge and violet as the inner edge. The pattern is ROY G BIV.

A rainbow is not an arch but a circle.
To the observer from the ground, the rainbow appears to be arch-shaped with its two ends meeting the ground. From the ground, only half of the rainbow is seen as it is cut by the horizon. To an observer from an airplane, the rainbow appears circle.

The dark sky between the primary and secondary rainbow is called Alexander’s band.
It is named after Alexander of Aphrodisias who first described the dark sky between the bands of two rainbows about 2000 years ago

The rainbow can’t be touched.
The rainbow is not an object to be touched as it is the result of the refraction and reflection of sunlight in rain droplets.

A rainbow formed by the light of the moon is called a moonbow or lunar rainbow.
The occurrence is rare as the moon should be bright enough and it should rain.

No two persons can see the same rainbow.
Two persons will see the rainbow from different angles as both of them are standing in different spots.

Rainbow is rarely seen in winter.
Due to a drop in temperature the raindrops freeze to form snowflakes causing the sunlight not to pass through the snowflake which prevents the formation of a rainbow.

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