Rainbows at Sea

by John MacFarlane 2014


Rainbow at sea. A second rainbow arc can be seen dimly to the right of the bright one. Notice the lighter sky ‘inside’ the arc. (Photo from the MacFarlane collection.)

On the east coast of central Vancouver Island it is easy to see rainbows. The showery weather, followed by sunny periods, so often associated with the Pacific coast of Canada is the cause. Late in the day when rising air lifts water vapour following rain creates the conditions necessary.

Each raindrop reflects the light and a rainbow forms in the sky focused exactly opposite the sun. It is the reflection that creates the rainbow.


A rainbow appearing over Chrome Island Lighthouse on the east side of Vancouver Island. (Photo from the MacFarlane collection.)

Under perfect viewing conditions the rainbow stretches from one side to the other touching the ground. The height depends on the altitude of the sun. If the sun is right on the horizon the rainbow is often a perfect semi–circle. When the sun is high in the sky the rainbows are more abbreviated. A second rainbow arc appears when the light bounces inside each raindrop and exits on the other side forming a second arc. The larger the raindrops the brighter the colours in the rainbow.

The colours always display with red on the outermost band ranging to violet on the innermost band. When a second arc appears the order of the colours is reversed in it and is invariably fainter than the primary arc.

To quote from this article please cite:

MacFarlane, John M. (2014) Rainbows. Nauticapedia.ca 2014. http://nauticapedia.ca/Articles/Rainbows.php

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