Sunset Rainbows and Solar Altitude

Reddened sunset rainbow Rainbow before sunset

The sun was less than 2 degrees above the horizon and the background is starting to take on twilight colours. There is still some blue in the rainbow but it is relatively weak. A faint secondary bow can also be seen to the left.

With the sun about 7 degrees above the horizon the sky is noticeably less reddened than in the example above. A yellowish supernumerary is distinctly visible in the lower section of the bow.

Unreddened rainbow well before sunset

With the sun 12 degrees above the horizon there is no perceptible reddening and the full range of colour is visible in the rainbow.

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