There’s always one thing that can brighten up a drizzly day, and that’s a rainbow. Arching across the sky, these spectacles of light are formed when moisture in the air interrupts the path of sunlight, splitting it up into all the colours of spectrum. You might be surprised to discover that raindrops aren’t their assumed ‘teardrop’ shape, but are spherical, an important distinction when it comes to making rainbows.
A raindrop’s spherical shape and increased density compared to air provide the conditions needed to bend light to the perfect rainbow-making degree. When sunlight passes through a raindrop, the direction the light is travelling is changed, known as refraction. The light is refracted as it enters the droplet, then internally reflected and sent back out the raindrop in the opposite direction, which is known as the angle of deviation.
When sunlight is refracted, it’s broken up into the individual wavelengths of light. The colours range from long wavelengths of red at the top of the rainbow through the seven visible colours in the light spectrum to shorter wavelengths of violet at the bottom. When sunlight is refracted twice in raindrops it creates a double rainbow effect. The double rainbow sits around ten degrees above the primary rainbow and its colours are inverted, with red at the bottom.
Did you know?
A record-breaking rainbow in Taipei lasted almost nine hours