Why do rainbows appear?

Rainbows appear due to reflection and refraction of light through the raindrop.

Most people wait for a rainy day, just to catch a glimpse of the colorful phenomenon that passes after the rain has subsided – the rainbow. Rainbow is a meteorological phenomenon that results from the reflection and refraction of light through a water droplet.

Let’s simplify this further – remember the famous experiment by Isaac Newtown where passing a light through a prism, which results in a band of colors? Well, something similar happens during rainbows as well. Just like the light passed through at an angle from the prism turns into a band of colors, the light passed through a water droplet results in the same phenomenon.

When light passes through the prism at an angle, it is refracted upon entering the prism, reflected on the inside of the prism and then refracted again when leaving it. In rainbows, the same thing happens but the prism is replaced with a water droplet.

Rainbows can only happen after rain or in places where water is in the air. They can also be caused by many forms of airborne water. These include not only rain, but also mist, spray, and airborne dew. Water droplets are required for the light to be refracted and reflected. The rainbow results in seven colors – Red, orange, yellow, green, blue, indigo and violet. These colors are shortened as ROYGBIV. The reason for the colors is because of the different wavelengths. At different angles, the different wavelengths are visible.

One must remember that a rainbow is not a physical object, but rather an optical illusion caused by water droplets and hence it cannot be touched. So, forget about the pot of gold that is believed to exist at the end of a rainbow. It is impossible for an observer to see a rainbow from water droplets at any angle other than the customary one of 42 degrees from the direction opposite the light source. Even if an observer sees another observer who seems "under" or "at the end of" a rainbow, the second observer will see a different rainbow—farther off—at the same angle as seen by the first observer.

Rainbows are usually seen in the western sky during the morning and in the eastern sky during the evening. In conditions of good visibility, a second larger rainbow can be seen above the primary rainbow, but with reverse color bands.

Image Courtesy: alkagirdhar.wordpress.com, bbc.co.uk

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