How a double rainbow is made

How a double rainbow is made
photo by Raynu Fernando

TUCSON, AZ (Tucson News Now) - Rainbows are common, but double rainbows are not.

The Tucson News Now crew had a great view of a double rainbow from our parking lot near Cortaro & I-10 Tuesday evening. The colors were some of the brightest and most vibrant I had ever seen in a rainbow.  A break in the clouds to the west allowed an opening for the setting sun to shine through the rain shaft over Tucson.

So, how is a double rainbow made?
First, let's start with a single rainbow.  Sun light is reflected and refracted through drops of rain.  The color and brightness of the rainbow depends on the angle and size of the rain drops.  Blue light is seen at a deeper angle than red light, which is why the color blue is seen on the inside of the rainbow, and red on the outside.

A double rainbow is when light is reflected not once, but twice through a raindrop.  The result is a secondary, inverted and dimmer rainbow outside of the primary.

Triple, or even quadruple rainbows are possible, but they need some help from other Earth-objects.  You may remember this picture (below), taken by Amanda Curtis in New York in April, of a quadruple rainbow when a double rainbow was reflected off of water in a nearby bay. 

image: Twitter Amanda Curtis

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