Subhorizon Red Rainbow  A capture by Franck Grondin (Frog 974 Photographies) as light rain fell close to sunset.  Réunion Island, "Cap Noir" viewpoint.

 All images ©Franck Grondin, all rights reserved. Shown with permission
Sub Horizon Bows

All rainbows are circular (or nearly so). They will form a full circle if allowed by plentiful raindrops in the right directions.

On level ground the path length from the eye to ground is not long enough to include enough rainbow forming raindrops. At most a faint bow is seen.

Climb a hill or mountain or stand on the Grand Canyon rim and there is a plentiful supply of rain along the rainbow cone.




Atmospheric
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The primary rainbow has its centre directly opposite the sun. At sunset or sunrise the bow is at its greatest possible height.

At sun heights above 42° the entire bow is beneath the horizon
                        

Red Bows

See them near to sunset and dawn.

Sometimes very red bows are seen just before sunrise or after sunset when the sun is still illuminating high falling rain.

Sunset sunlight travels through much more air before reaching us. Air molecules scatter away more violets, blues and greens leaving highly reddened rays to make the rainbow.

Dust, aerosols, atmospheric moisture and the rainbow's background also influence the appearance.

Every rainbow is different in its own way.