Why is there sometimes a big ring around the moon?

Question

Have you ever looked up at the moon and see a huge perfect circle of light around it, well what causes this?

Answer 1

It is an optical effect caused by ice crystals in the atmosphere. It is similar to a rainbow, which is caused by water droplets in the air.

Answer 2

I've heard that means you can expect precipitation within the next 48 hours. I don't know what evidence there is to back that up. It may be an old wive's tale. I know that any time I notice it, according to the forecast, it seems to have been true.