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The BBC News item Double reflected rainbow photographed in Orkney shows an unusual kind of double rainbow.

According to the article:

The image was captured by Martin Gray at Gyran on Tuesday morning, who described the sight as "amazing".

He said: "I'm used to seeing double rainbows, but this was a really weird-looking thing."

[...]

"I quickly snapped a few photos. It was extremely bright, and odd looking - all odd angles. "But I didn't even notice the faint fourth arc until I carefully looked at my photographs."

BBC weatherman Simon King said it was an "impressive" photograph. "It's a really impressive double reflected rainbow," he said. He said the photographer had a loch behind him at the time.

As a result, sunlight had bounced off the loch before reaching the water droplets from a rain shower in front of him. The sunlight was then bent and reflected inside the droplet back to the photographer.

Question: I've annotated the image and numbered each of the arcs. Is it possible to sort out what's going on and which phenomenon are responsible for each of them?


double reflected rainbow (BBC, Martin Gray at Gyran)

Credit: Martin Gray & BBC; Gyran, Orkney Islands, Scotland

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What you are seeing are a primary rainbow (rainbow #2 in the linked image), its secondary rainbow (#4), a reflection rainbow (#1), and its secondary (#3).

Note well: The linked article called these reflected rainbows, but that is incorrect. A reflected rainbow is yet another atmospheric optical phenomenon that occurs when one sees what appears to be the reflection of a rainbow on water in front of the viewer. The water was behind the photographer in the linked image, and the extra two rainbows were in the sky rather than in the water. (There is no water in the linked image.)

The reflection of the Sun off of the water behind the viewer result in a reflection rainbow in front of the viewer. The center of a primary rainbow is the antisolar point from the perspective of the viewer of the rainbow, which is below the ground. The center of a reflection rainbow is the anthelic point of the reflection of the Sun, which is above the ground. Thus rainbow #1, the primary rainbow from the Sun itself, is lower than rainbow #2, the primary rainbow from the Sun's reflection off the loch behind the photographer. The two rainbows intersect at the ground.

Rainbows can have secondaries, and so can reflection rainbows. These are bows number 4 and 3. Note that the sky and land are darker between the primary and secondary, brighter outside the secondary, and much brighter inside the primary. The lighting outside the secondary is the natural lighting level.

One way of looking at rainbows is that they transfer some of the light that would normally fall between the primary and secondary to inside the primary, and that this transference changes a bit with frequency.

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  • $\begingroup$ Thanks for the great answer! You're explanation is excellent, but I've added some supporting links which also seem to be helpful for some readers. I can put them in a comment instead if you like. $\endgroup$ – uhoh Oct 30 '19 at 13:40

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