Have you ever wondered why rainbows are arched? The reason is an optical illusion created by round water droplets, BBC Star at Night Magazine reports.
Rainbows form when the sun is shining and there is a lot of moisture in the air, creating water droplets — for example, when it rains or near waterfalls.
When sunlight hits a droplet, some of the light is reflected back from its surface, while some passes through it. As the light passes through the droplet, it refracts, and the same thing happens when the refracted light touches the surface of the droplet again at a different point. Some of the light travels out of the droplet again, while some is reflected back into it.
Some of this bouncing and refracted light eventually reaches our eyes. The result of all these reflections and refractions is that the light we see is split into its component wavelengths.
For example, red light refracts at 42°, while violet light refracts at only 40°. This is why we see a band of light in different colours, or a rainbow. However, this only occurs when light hits our eyes at the correct angle.
Since raindrops are spherical, the result is a curved — or, more accurately, circular — rainbow. We usually see a rainbow from the ground, which is why we can only see half of it. The other half of the circle actually exists, but it is hidden from us behind the horizon. Therefore, if you were to embark on a fantastic journey across the rainbow one day, you would eventually end up where you started.
