Halo around the moonJanuary 9th, 2012 at 10:36 am by Amelia Segal under 4 Warn Weather
A halo around the moon (or sun) is caused by cirrostratus clouds. These are high altitude clouds, typically at 20,000 to 26,000 feet. Cirrostratus contain ice crystals, moonlight hits these crystals and forms a halo. Seeing the halo can mean inclement weather within the next 24 to 48 hours because the clouds can be followed by altostratus then nimbostratus clouds.