Tuesday, September 1, 2015

Who is Roy G. Biv and how does he control the color of the sunrise?

Red sun over Gratiot County

Have you ever wondered why the sun looks red or orange when it is near the horizon?  This morning on my drive to work I stopped to photograph the reddish-sun just a few degrees over the horizon.

The sun looks like this because of the properties of light.  The visible light spectrum (the light we can see) that comes from the sun is divided into seven colors red, orange, yellow, green, blue, indigo, and violet - ROYGBIV.  In order to remember the colors of the visible spectrum, just remember the acronym Roy G. Biv.

The colors that make up Roy's name are made of different wavelengths of light.  Red light has the longest wavelengths and violet has the shortest; the colors in-between have wavelengths in-between.

When light from the sun enters our atmosphere it is refracted (bent) and scattered by particles found in the atmosphere.  When the sun is overhead it has very little atmosphere to travel through so little of the light is scattered.  However when the sun is at a low angle such as near sunrise or sunset the light has to travel through more of the atmosphere before it reaches a viewer.  When it takes this longer path there is more opportunity for the light to be bent and scattered.

Colors that have the shortest wavelengths (indigo and violet) are scattered the most.  Colors that have the longest wavelengths (red and orange) are scattered the least, causing the sun to appear red or orange at sunrise and sunset.

Roy G. Biv watches the sunrise

To learn more about Roy G. Biv and the visible spectrum of light check out this post about rainbows from September 2014.

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