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Posted by on Apr 23, 2016 in Tell Me Why |

When Can a Rainbow Be Seen?

When Can a Rainbow Be Seen?

After a shower of rain there is often a rainbow. Rainbows form when the sun begins to shine through the clouds while the air is still filled with raindrops. The raindrops act as tiny prisms to separate sunlight into the colors of the spectrum, and an arch of colors appears in the sky.

The many colors in a rainbow blend into one another so that we rarely see more than four or five clearly. You’ll miss it if you face the sun. A rainbow can only be seen if you face the sky with the sun at your back. Little rainbows can often be seen in the spray of a lawn sprinkler.

A rainbow is not an object; it cannot be approached or physically touched. It is a multi-colored arc that forms in the sky which is created by both reflection and refraction (bending) of light in water droplets in the atmosphere, which results in a spectrum of light appearing.

A rainbow is in fact a full circle of light. However, due to most people viewing a rainbow on the ground we only see a semi-circle or arc of the rainbow. Rainbows can be seen not just in rain but also mist, spray, fog, and dew, whenever there are water drops in the air and light shining from behind at the right angle.

The sky within a primary rainbow is brighter than the sky outside of the arc. This is due to the fact that the millions of droplets needed to make a rainbow are spherical and overlap to create white light. At the edge however, these colored discs don’t overlap so display their individual colors producing the rainbow arc.

A “double rainbow” is where a second, much fainter arc can be seen outside of the primary arc. This is caused by the light reflecting twice inside the water droplets. As a result of this double reflection the colors of the second arc are inverted with violet on the outer edge and red on the inner edge.

Very rarely, light can be reflected 3 or 4 times within a water droplet which produces even fainter tertiary (third) and quaternary (fourth) rainbows in the direction of the sun.

Content for this question contributed by Jason Purdue, resident of Santa Rosa, Sonoma County, California, USA