What is a rainbow and its formation?

What is a rainbow?

• Rainbow is the colored display in the form of an arc of a circle hanging in the sky observed during or after drizzle appearing on the opposite side of sun. rainbow is formed due to dispersion of sun light by the suspended water droplets.

• Rainbow is of two types.

1. Primary rainbow.
2. Secondary rainbow.

• Primary rainbow is formed due to two refractions and one total internal reflection of light falling on the raindrops. In the primary rainbow, the red color is on the convex side and violet on the concave side. Primary rainbow has an angular width of 2 degree at an average angle of elevation of 41 degree.

• Secondary rainbow is formed due to two refractions and two internal reflections of light falling on rain drops. The order of color on the secondary rainbow is in the reverse order and has an angular width of 3.5 degree at an average elevation of 52.75 degree. Secondary rainbow is less intense than primary rainbow.

What makes a double rainbow?

Sometimes you can see another fainter secondary rainbow above the primary rainbow. The primary rainbow caused from one reflection inside the water droplet. The secondary rainbow is caused by a second reflection inside the droplet. And this re-reflected light exits the drop at a different angle (50 degree instead of 42 degree for the red primary bow). This is why the secondary rainbow appears above the primary rainbow. The secondary rainbow will have the order of the colors reversed too. With red on the bottom and violet on the top.