Refracting light path of Solar Halo
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A day in May being a pale cloud covered the whole sky, a excellent solar halo was appeared surrounding the sun perfectly.
The solar halo is an atmospheric optical phenomenon that can be seen unexpectedly frequently for example when the weather is changing for the worse.
The halo has a radius of about 22 degrees, and sometimes it's called "inner halo" or "22 degrees-halo".
When the hexagonal ice crystals are distributed at random in higher sky,
the refracting angle of sunlight that enters and exits the side planes of the crystal as the figure shown is equivalent to about 22 degrees.
Because ice crystals are facing various directions and floating in the sky, we can observe the refracted sunlight as a circle of light with a radius of 22 degrees.
Actually the solar halo has one more kind that appears at the position of 46 degrees in radius called "outer halo" or "46 degrees-halo".
The outer halo appears by sunlight that enters the vertical prism face and exits at bottom basal plane (or reverse) of ice crystal.
But the halo looks extraordinary dimmed so we can hardly observe.
Other images of Halo
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