How Do Double Rainbows Form? - WAOW - Newsline 9, Wausau News, Weather, Sports

How Do Double Rainbows Form?


A few weeks ago North Central Wisconsin was treated to a double rainbow.  This phenomenon can be a magnificent and rare site to see.  So how does this happen?

One thing to note first: The suns locations and the location of an observer will play a factor in the angles and how high a rainbow will be in the sky.

A basic rainbow occurs when lights shines onto moisture.  Rainbows can occur in any form of water including rain, waterfalls, mist or even dew. The sun will always be behind you when you look at a rainbow and the rain will always be ahead of you. The colors of the rainbow are the colors of a continuous spectrum with everything from red to violet; this is because sunlight is white which is made up of the whole spectrum of colors.  The rainbow is actually an infinite amount of colors but we classify them as Red, Orange, Yellow, Green, Blue, Indigo and Violet. 

Alright the basics happen like this; when a beam of light hits a raindrop it gets refracted on the way in and the way out.  The first refraction will form the primary rainbow.  But a few of these beams will bounce of the raindrop not once but twice.  It is the secondary beams that bounce back that end up forming the second rainbow about 9 degrees above the first rainbow.  Also, since not every beam is bounced back twice the second rainbow will always be dimmer.

Not only will the secondary rainbow be dimmer but it will also be inverted in the colors.  Blue will be on the outside and red on the inside. 

For any other questions related to rainbows this is a detailed but easy to understand site.

Meteorologist Kristen Connolly

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