The bright circle around the Sun seen in the picture is known as a halo. What causes it?
refraction of light in ice crystals
refraction in the lens of the eye or lens
refraction of light in water drops
reflections from the water surface
Halo is the name for a family of optical phenomena produced by light interacting with ice crystals suspended in the atmosphere. Halos can have many forms, ranging from colored or white rings to arcs and spots in the sky. Among the best known halo types are the circular halo (properly called the 22° halo),  Other common optical phenomena involving water droplets rather than ice crystals include the glory and the rainbow.  
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refraction of light in ice crystals
refraction in the lens of the eye or lens
refraction of light in water drops
reflections from the water surface
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