The solar and lunar halos are luminous circles formed around the Sun and Moon, respectively, as a result of reflections and refractions suffered by light in contact with ice crystals.
- Why does it occur?
The solar or lunar halo occurs in the troposphere , the lowest portion of the atmosphere , with altitudes of 17 km to 19 km in the region of the Earth’s equator. In this region of the atmosphere, light from the Sun or light reflected by the Moon is refracted and reflected by small hexagonal ice crystals. By virtue of the shape and orientation of the ice crystals, the halo is formed.
Why are rainbow colors seen in the solar halo?
The formation of the rainbow coloration in the solar halo occurs because of the phenomenon of light scattering , which enters the ice crystals as polychromatic (white) light and, after undergoing two consecutive refractions (air – ice and ice – air), it is spread out in its seven colors .
The ice crystals play the role of the prism seen in the image above. When light hits them, a small portion is reflected and most undergoes refractions that cause the light to scatter.