Extensive Definition
An anthelion (plural anthelia, from late Greek
ανθηλιος, "opposite the sun") is a rare optical
phenomenon appearing on the parhelic
circle opposite to the sun as a faint white halo,
not unlike a sundog.
How anthelions are formed is disputed. Walter
Tape, among others, has argued they are not separate haloes, but
simply where various haloes caused by horizontally oriented
column-shaped ice crystals
coincide on the parhelic circle to create a bright spot. If this
theory is correct, anthelia should only appear together with these
other haloes.
However, anthelia occurs unaccompanied by other
plate crystal haloes, why other scientists have produced
alternative explanations. The Dutch professor S.W. Visser proposed
they form by two exterior light reflections in quadrangular prisms,
while Robert Greenler has suggested two interior reflection in
column-shaped crystals produces the phenomenon.
See also
References
External links
- Earth Science Picture of the Day, April 26, 2006 - Photo of an anthelion and anthelic arcs display in Germany February 2006.