A rainbow in the full moon light!

When the sun light is reflected and diffracted in fine water droplets in the air, a rainbow arises. So what happens if the same occurs in the moon light, is there also going to be a rainbow? Well, we find the idea of a moon rainbow quite fascinating …

Let’s take a short detour into physics. What we recognise in a rainbow as an arched bow made of colourful light, are the spectral colours that develop when the “white” sunlight fans out in its different wavelenghts, which we perceive in different colours. This decomposition does also take place, when the light  is sent through a glass prism.

Now it is getting interesting, even though moon light is reflected sun light (that shines onto the moon from the sun and arrives on earth this way), but the light seems to be compounded quite differently, it is more bluish. Furthermore, it is clearly less bright. Insofar, the question remains, whether the moon light is sufficient to diffract in water droplets and to create a rainbow?

In times of the Internet, one does not have to anticipate for decades to witness such spectacle, but reaches the moon rainbow via Google. And indeed, this phenomenon exists and surprises us with its rare occurence and some characteristics:

Firstly, the moon rainbow appears less during rain, but more so where large amounts of atomised water is dispersed into the air and where it is otherwise a cloudless, clear sky: in the surrounding of great waterfalls. There are many examples of the Victoria Falls in Africa, the Yosemite Falls or the Cumberland Falls in the USA.

Secondly, the moon rainbow appears to be visible to the naked eye as a bright bow and only a photo camera is able to depict the typical colour spectrum. At least, this is what some observers report. Amongst them a visitor on our full moon pages and her full moon experience. Coincidentally, you can read that the moon rainbow can quite possibly arise together with a nightly shower of rain.

Moon rainbows are a bit of nocturnal magic. And who would not want to experience this?

Column: Worth seeing | 4 comments | Leave a comment
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  • I have seen two rainbows by moonlight. Both were in the California desert, one at Llano, California about 1959 perhaps after a rain in a distant area east of where I stood and my visibility was 30 miles or more, another around 1961. Not sure if it had rained in the area I was approaching. I believe I was driving my car on that second occasion. Both rainbows were white. No other colors visible. It was an unmistakable sight. Not a hallucination. Lovely. I wrote a poem mentioning it.

  • I have seen this 3 times over the years. On each occasion late in the evening, say after 21.00, a reasonably clear night with a bright moon and isolated showers. Most people do not even consider that such a thing is possible.

  • beautiful and serene

  • Just beautiful

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