Explanation:
Have you ever seen a halo around the Sun?
This fairly common sight occurs when high thin clouds containing millions of tiny
ice crystals cover much of the sky.
Each
ice crystal acts like a miniature lens.
Because
most of the crystals have a similar
elongated hexagonal shape, light entering one crystal face and exiting
through the opposing face refracts 22
degrees,
which corresponds to the radius of the Sun Halo.
A similar Moon Halo
may be visible during the night.
The picture was taken in Gunlock,
Utah,
USA.
A flock of birds was caught by chance in the foreground.
Exactly how
ice-crystals form in clouds remains under
investigation.
Lecture: APOD editor to give public talk in Princeton tonight (April 11)
