MEMPHIS, Tenn. (WMC) -MEMPHIS, Tenn. (WMC) - Have you ever looked up into the night sky and noticed a ring around the moon?
This cool sight is reflections of ice crystals in the upper atmosphere from a deck of cirrus or cirrostratus clouds. This is referred to as the halo effect, a winter halo, or some call it a 22 degree halo and it is caused by light rays diffracting around the moon.
The clouds are situated about twenty thousand feet up and are thin wispy cirrus clouds. These clouds can be so thin that you may or may not be able to see them, but these thin clouds are more noticeable when the light from the moon reflects on those tiny hexagon-shaped ice crystals. The light rays coming from the sun that are then reflected on the moon are bent by the crystals 22° away from the moon. This creates a halo that has a 22° radius (44-degree diameter).
The halo around the moon is most common in winter months because we are in the cool season, but can happen in any season. This can also happen in tropical and hurricane systems too because there are high thin clouds surrounding the outskirts of those systems.
These halos can also look like faint rainbows with red color on the inside, and a blue outside. The full process is due to refraction, reflection, and dispersion. They are caused by the same effect, because the ice crystals are 6-sided prisms.
One weather folklore says a ring around the moon means precipitation soon because high cirrus clouds often come before a storm. So there is some truth to the weatherlore. Cirrus and cirrostratus clouds are often precursors for storm clouds behind them, because they are most often the first cloud layer seen when a weather system approaches. However this is not always the case.
If you spot a moon halo, you may notice more red on the inside and more blue on the outside of the halo. These colors are more noticeable in halos around the sun. If you do see a halo around the moon or sun, notice that the inner edge is sharp, while the outer edge is not as sharp.