Monsoon Astronomy: Rainbow Rings and Halos

Thursday, 12 June 2014 - 11:26am IST | Place: Mumbai | Agency: dna

While monsoons are still teasing us with the occasional drizzle, Arvind Paranjpye tells us about the multi-hued majestic phenomena the rains promise to bring

Our childhood fascination for a lot of things give way to new awe-inspiring experiences, but a rainbow brings a smile to every face at any age. But do you know why no one found any gold at the end of a rainbow? Because a rainbow has no ends. Although you can only see an arc from ground level, if you're on a flight you'll be able to see the entire ring of the rainbow!

Come monsoon and the sky is filled with moisture and tiny droplets of water left behind by light showers. Sunlight enters these droplets, refraction (turning or bending of a wave–such as a light or sound wave–when it passes from one medium into another having different optical density) and dispersion causes it to split into different hues to give you a beautiful band of colours against the backdrop of fresh air and lovely skies.
We usually associate rainbows with the sun, but did you know the moon can cause rainbows too? Try to see it on June 13 and even a few days later when it is quite likely to occur.

Another interesting, ringed phenomena you can witness in the coming months are halos, which are not only caused by both the sun and the moon, but also encircle the sun and the moon with its white light.
When light rays from the sun or moon pass through ice crystals present in cirrostratus clouds, which are about 5-10 km above the ground level, the hexagonal shape of the crystals causes the light of these celestial bodies to bend in such a way that a white ring forms around them. The diameter of the ring is 44 degrees, which is slightly more than what can be photographed with regular cameras. On a clear day with blue skies, when the crystals are also clear, these crystals will act like prisms when clouds float over the sun or moon and will break into a spectrum of rainbow colours. And just like the rainbow, you won't need any equipment to enjoy this spectacular gift of nature.

But unlike the case of the rainbows, where the sun or moon has to be behind you for you to be able to see it, in case of halos the sun or moon is in front of you. Moreover, while rainbows occur post or sometimes even during light showers, halos may herald that a shower is expected in the next 24 hours.


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