Rainbow is one of the most amusing atmospheric phenomena across the globe. What is a rainbow exactly and how does this magical spectacle forms? For centuries it has always being a captivating color display. It’s magnificent impact of dispersion of light and proof that visible light compose of spectrum of wavelengths, associated with distinct color. The word rainbow comes from the Latin phrase “arcus pluvius”, meaning “rainy arch.”
Although it is a full circle, it can only be seen as semi-circle from ground level. But from above the earth such as in an airplane it is sometimes possible to see a rainbow as a full circle. It is an optical illusion because it does not really exist in a specific spot in the sky. It does not have an end. There are variation of rainbow which include full-circle, twinned, double, supernumerary, monochrome, fogbow, moon bow, sleetbow, reflected and reflection rainbow.
Its colors include red, orange, yellow, green, blue, indigo, and violet (ROYGBIV is an acronym you can use to remember the colors). However, to view a rainbow, observer back the sun at an approximately 42 degree angle above the ground to the atmospheric region with suspended water droplets or mist. The lower the sun, the more arc of rainbow the observer see. And everyone sees rainbow differently because each person eyes sees it in different way. It is not only cause by rain but many forms of airborne water which include mist, spray, and airborne dew.
Hawaii is refer to as the rainbow state because it has the most rainbows on earth. The world’s longest observed rainbow was seen in the high mountains of Taipei, Taiwan in 2017. It lasted for 8 hours and 58 minutes.
How Rainbow is Formed
The formation entails physical phenomenon, which includes dispersion, refraction, reflection and total internal reflection. Rainbows form when light from the sun is disperse by water droplets (e.g. raindrops or fog) through a process called refraction. Firstly, refraction occurs when the light from the sun changes direction when passing through a medium denser than air, such as a raindrop.
Once the refracted light enter inside the raindrop, it bounces back instead of passing through the drop. Upon exiting the raindrop, the light undergoes another round of refraction. That is, refracted light enters the raindrop twice and reflecting once, the light ray is dispersed and bent downward towards an observer eyes.
The reduction of speed makes the path of the light to bend. This is the reason it is always curve or bend towards the normal line. Each color bends at a different angle based on its wavelength. Violet and blue has shortest wavelength bends the most, while red, has the longest bends. Moreover, the position of the sun and the raindrops in relation to the observer need to be just right for a rainbow to form.
In short, you can create yours as well, to experiment the science behind it and it can be fun. There are different ways to form a rainbow. For instance, turn on garden hose on sunny day, stand with your back against the sun, then you can see your rainbow. Also, you can fill a clear glass with some water, in a darkened room. Shine flashlight at one side of the glass at an angle, aiming for the water. The light will refract and separate within the water, projecting a rainbow onto a nearby wall or screen.