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Reflection Rainbow
10/28/2002
Listen in RealAudio 
We generally think of rainbows as forming from direct sunlight bouncing off a sheet of
raindrops, but any bright light source-even the moon-can produce a rainbow, and so can
reflected light. Hi, I'm Bryan Yeaton for The Weather Notebook.
A reflection rainbow develops when light - usually from the sun - first reflects off a surface
such as a large body of water and then strikes the raindrops, producing the bow through
internal reflection and refraction.
Reflection rainbows are usually seen when the sun is low and the water surface very calm,
allowing for near-total reflection of the solar light. Thus the rainsheet from which the bow
forms sees two distinct suns - the actual sun above the horizon and the reflected solar orb
below the horizon. The result is two distinct rainbows with discrete centers.
The reflection rainbow always forms higher in the sky than the direct-beam rainbow, with its
center above the horizon. The reflection bow arc intersects with the standard rainbow at the
horizon.
The reflection rainbow should not be confused with the secondary rainbow which may sometimes
be seen outside the primary bow; this is formed through a second reflection within raindrops.
However, in some circumstances, both the direct and reflection rainbows may sport a secondary
bow.
Light from a rainbow can also strike a reflecting surface and produce an apparent mirror
image. But don't be fooled. This reflected rainbow is not the reflection of the rainbow you
are seeing in the sky, but the reflection of an entirely different rainbow formed from another
set of light rays and raindrops.
Thanks to contributing writer Keith Heidorn for this story. The Weather Notebook is brought to
you through the generous support of the National Science Foundation, and Subaru of America.
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