Illustration shows the passage of light through a rain drop.

Of the several rays incident on the drop we are interested in the behavior of the rays that produce the primary rainbow and the secondary rainbow.

Partial reflections and refractions occur at every point where the ray is incident but only relevant reflections and refractions are shown.

Primary rainbow is due to the rays incident on the top portion of the drop and secondary rainbow is due to the rays incident on the bottom portion of the drop.

The primary rainbow would be between angles of 40° and 42° to the horizontal and secondary rainbow between angles 51° and 53° to the horizontal. These are the rays that suffer minimum deviation as they are reflected and refracted and hence are brightest.

In the graph option observe the way the deviation is measured.

Observe the order of colors in the primary and secondary rainbows.