Ask the meteorologist: What is that ring around the sun?

Question: What is that ring around the sun?

Answer: Most of us have looked up and caught a view of the occasional halo or "sun dog," perhaps (although they are less frequent) even a brightly colored circumzenithal or circumhorizon arc.

There are a number of weather phenomena that can create the appearance of a ring around the sun.

A fully formed and reasonably bright halo is typically associated with large numbers of six-sided, columnar ice crystals that are "poorly oriented, " meaning they are tumbling such that the individual crystals are tilted in a variety of directions.

Refraction of the light through the ice crystals in the atmosphere produces a halo, and where differing wavelengths of light are refracted to a slightly different angle creates the appearance of the colors of the rainbow.

Sun dogs are most easily formed and seen when the sun is low in the sky, not too long before sunset or after sunrise, and are visible rather frequently.

A circumhorizon arc is caused by the same plate-like crystals that create the sun dogs, but is much less frequently seen, in part because they are only visible when the right kind of clouds are in place AND the sun is at an elevation of 58 degrees above the horizon or more. In North Carolina, they are most likely a spring and summer event.

In some cases, otherwise similar ice crystals are shaped in a way that leads them to mostly be oriented in the same direction. When that happens, you will not see a circle around the sun but instead other phenomena such as a circumzenithal arc – which can look like an upside-down rainbow – or parhelia – which looks like bright spots on one or both sides of the sun.

Other times the crystals may not be well-formed or the cloud may be too thick to transmit sufficient light, in which case no halo will be visible.

By the way, although we don't always notice them, because sometimes they are faint, partial or occur at night, halos are not especially uncommon. For our area they probably occur around 80-90 times per year.