Rainbows

In this rainy season you get to see rainbows frequently. Though they are not always prominent or a complete semi-circle. The other day I spotted a beautiful rainbow from horizon to horizon.

Even a more beautiful shot was taken by one of the employees at our Bantala office.

Now, this is a rare photo. The rainbow is so very bright and prominent. You can even see a secondary rainbow outside the primary one.

Secondary rainbows are caused by a double reflection of sunlight inside the raindrops, and appear at an angle of 50–53°. As a result of the second reflection, the colours of a secondary rainbow are inverted compared to the primary bow, with blue on the outside and red on the inside. The secondary rainbow is fainter than the primary because more light escapes from two reflections compared to one and because the rainbow itself is spread over a greater area of the sky

If you see closely there is also a faint rainbow on the inner side of the primary rainbow. That is called a supernumerary rainbow (also known as stacker rainbow). Supernumerary rainbows are caused by interference of light.

The alternating faint rainbows are caused by interference between rays of light following slightly different paths with slightly varying lengths within the raindrops. Some rays are in phase, reinforcing each other through constructive interference, creating a bright band; others are out of phase by up to half a wavelength, canceling each other out through destructive interference, and creating a gap. Given the different angles of refraction for rays of different colours, the patterns of interference are slightly different for rays of different colours, so each bright band is differentiated in colour, creating a miniature rainbow. Supernumerary rainbows are clearest when raindrops are small and of similar size. The very existence of supernumerary rainbows was historically a first indication of the wave nature of light, and the first explanation was provided by Thomas Young in 1804
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