You might have seen a rainbow-like arc or a circle around the son or the moon. Halo is an optical phenomenon which means because of the properties of light such as reflection and refraction we can observe this incident.
Among scientists it is known as 22-degree halos because the radius of the halo is approximately 22 degrees to the observer.
Feeling confused? Just see the illustration below.
Mechanism of how sun halos occur
In the upper troposphere of earth atmosphere, which extends from 5 to 10 km from the earths surface contains ice crystals. Ice crystals are responsible for this optical phenomenon. When the sunlight falls onto ice crystals they reflect and refract light like prisms and mirrors. This reflection and refraction of light can result in arcs, white or colorful circles and beams of light as discussed below.
Ice crystals are found in cirrostratus clouds in the troposphere.
The pattern of halo noticed is caused by the crystals’ specific form and orientation. Because of dispersion, light is reflected and refracted by the ice crystals and may divide into colors.
Do sun halos predict anything?
There’s a historical meteorological saying that says a ring around the moon signals rain is on the way. This saying holds true because dense cirrus clouds sometimes precede a storm.
Because the cirrostratus clouds that generate the halos might imply rain, they frequently do suggest that rain will occur within the upcoming 24 hours.
Moon halos or Lunar halos
Lunar halos are mainly colorless since moonlight isn’t particularly bright, although you may see redder on the interior and bluer on the outside of the halo. These hues stand out stronger in halos surrounding the sun.
Once you do observe a halo around the moon or sun, notice how the inner edge is sharper than the outer border. Also, the sky around the halo is darker compared to the other areas of the sky.
Sun Pillars and Sun dogs
Sun pillars and sun dogs are also other optical phenomenon that can rarely occur with sun halos. Since the phenomenon are not common it might be difficult to predict them as well.
Sun pillars or else in other words light pillars arise from either the sun or the moon or any other bright source of light such as a street light. It is a vertical column of light which can be sometimes visualized below the sun in high altitude areas. The phenomenon is caused by hexagonal plate- and column-shaped ice crystals.
Sun dogs are often seen as a pair of softly colored light patches on the Sun halo in its left and right sides. It is an optical phenomenon in the atmosphere that consists of a luminous spot on one or both sides of the Sun.