Explanation for an unexpected rainbow Yesterday, I observed an unexpected rainbow in the sky. There was no forecast for rain, neither was it raining anywhere nearby. I have been trying to find an explanation but don't seem to find any. Can someone please explain what this rainbow is?
Note:the colours were way more vivid as compare to the picture I have taken

 A: These are tropospheric Iridescent Clouds
According to AtmosphericOptics:

When parts of clouds are thin and have similar size droplets, diffraction can make them shine with colours like a corona. In fact, the colours are essentially corona fragments. The effect is called cloud iridescence or irisation...
The usually delicate colours can be in almost random patches or bands at cloud edges. They are only organised into coronal rings when the droplet size is uniform right across the cloud. The bands and colours change or come and go as the cloud evolves...Iridescence is seen mostly when part of a cloud is forming because then all the droplets have a similar history and consequently have a similar size.

I've saturated the image so the interesting part can be appreciated

And here you have a very similar observation I quickly found by google image search:

A: I don't see a rainbow in that photo but rain isn't always necessary for a rainbow to form. A rainbow results from water droplets refracting and reflecting light in a certain way. Suspended water droplets (fog) can be enough, if they are sufficiently dense, occupy a sufficiently large volume and are located in the direction where you would normally see a rainbow.
