The cause of sun halos are water droplets and moisture that is around the sun and when the light refracts through the water droplets it creates the sun halo.
It's basically what happens when you see a rainbow in the sky after the rain happens.
A rainbow which is also pretty happens as a result of water droplets and sunlight refracting through the water droplets.
When a halo happens around the sun it usually symbolizes and means that snow or even just rain is on the way.
That halo also means god as it's believed that you get a halo when you go into heaven.