Regularly, I see rainbows around the moon. Here is approximately what I see:

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Right at the edge of the moon, I see a bright blue ring of light. Further out, I see an inner rainbow. This is not as bright as the ring, but is still clearly visible. Even further out, I see an outer rainbow that is very faint.

I see the blue ring during every full moon. I see the rainbows more frequently in late fall and winter than in spring or summer. But every year, I see these moon rainbows during a full moon.

Since I see these moon rainbows more frequently in late fall and in winter, are these moon rainbows caused by moonlight reflecting off of ice crystals in cirrus clouds high up enough that I can't see the clouds? Also, why do I see a bright blue ring right at the edge of the moon during every full moon?

  • $\begingroup$ Does it look like this? (Google Moon dog) google.com/… $\endgroup$ – userLTK Aug 23 '19 at 4:34
  • $\begingroup$ No, I just see the rainbows around the moon. I don't see moon dogs with it. $\endgroup$ – Caters Aug 23 '19 at 4:36
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    $\begingroup$ Do you wear thick eyeglasses? $\endgroup$ – Koray Aug 23 '19 at 8:51
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    $\begingroup$ Does it look like apod.nasa.gov/apod/ap150615.html ? $\endgroup$ – samcarter_is_at_topanswers.xyz Aug 23 '19 at 11:55
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    $\begingroup$ +1 just fyi, questions like this (atmospheric effects in the sky) can also be asked in Earth Science SE $\endgroup$ – uhoh Aug 23 '19 at 15:20

There are a couple of atmospheric phenomena that can create rings around the moon.

Corona are caused by water droplets diffracting the moon's light, they are fairly small, and close to the moon. They are coloured but not as brightly as a rainbow. Our eyes are also not so good at seeing colours in dim light.

The 22-degree halo is a larger ring, as big as two hands stretched out at arms length. Solar halos are clearly coloured, lunar halos are dimmer and I haven't seen lunar halos that are bright enough to appear coloured to me.

An eye condition, astagmatism, can also create rings, such as the "thin blue ring" (though I am not a doctor) You may be seeing a combination of all three at various times.

  • $\begingroup$ This is the answer in my opinion and plus 1. However a corona can be spectacular and not that small. If one get to see a perfect corona, it is either wow or "scary" without previous knowledge. Tip: for capturing it with a smartphone put metering on full screen and use a sensitive setting. The moon will be a white fuzzy disk but one catch easily two orders of refraction (two inverted rainbow rings). Also add that C is due to diffraction while H are refractive phenomena. $\endgroup$ – Alchimista Aug 26 '19 at 9:36

I think you very nearly answered your own question. The rainbows are indeed due to light diffracting off high altitude ice crystals, but more in a kind of haze than in the form of clouds. I have seen something similar in Hereford UK, but only on very rare occasions. There must be something unusual about the climate where you live for you to see them so often. The other unusual thing is for you to see the colours so clearly. The human eye loses colour vision at night, though with a very bright full moon there is still a vestige of colour vision left. The fact that your concentric rings are off centre and slightly elliptical I put down to imperfect draughtsmanship rather than faulty vision.


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