Today was one of the rare clear sunny days in my city, and I was watching the Sun for several hours. When looking with naked eyes at the sky very near the Sun, standing on the border of a shadow of a building, I noticed that, despite there were no clouds anywhere near the Sun, the light-blue sky had a triple rainbow, like in the image below (the Sun disk is right behind the border of the building):
This reminded me of halo, but the latter seems to
- Appear in cold weather
- Be much more pronounced
- Have only one rainbow, not triple
Also, the above image is visible by naked eye only after you stare at the sky for about five seconds, when the eyes adapt to the brightness — unlike halo, which is easily visible immediately.
It's more similar in how it looks to cloud iridescence. But again, there were no visible clouds anywhere around the Sun — the day was unusually clear. Also, cloud iridescence seems to make clouds colorful much farther from the Sun's disk that what I observed today.
So I now begin to think that the Sun is always surrounded by a rainbow similar to the above, even in clear weather. My question is, is this true? Or does it depend on weather (humidity?), geographical latitude, season?