Rainbows, Halos,
And Glories
( ....and sun dogs,
and supernummary
rainbows, and
coronas,
and sun pillars)
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At our January SRHR meeting, Dr. John Adam gave a
delightful talk entitled "Rainbows, Halos, and Glories", explaining
the many visual atmospheric displays we see in the sky from time to
time. Dr Adam is Designated University Professor of Mathematics
(for excellence in teaching) at the Old Dominion University (Virginia)
Department of Mathematics and Statistics. He is author of
the book, "Mathematics
in Nature: Modeling Patterns in the Natural World", published by
Princeton University Press (2003).
This description of his talk pales (literally) in comparison to the
vivid slides of brightly colored atmospheric phenomena that Dr. Adam
showed. The one unfortunate note in his address, however, was
his insistence that the alien mother ships clearly evident in some of
his pictures could be explained away by refraction and other
polysyllabic "scientific" jargon.
He first explained the primary rainbow (due to two refractions and
one reflection inside mostly-spherical water droplets), located at
42 degrees away from the anti-solar point, and the secondary rainbow
(due to two refractions and two reflections inside the droplets),
located at 51 degrees away from the anti-solar point. The
anti-solar point is the point on a viewer's horizon that is directly
behind him as he views the sun,
ie, it is the point on the 360 degree horizen that is 180 degrees
from the sun. In addition to that, he showed the "Alexander's
Dark Band" between the the two rainbows, and the supernumerary bright
bands located below the primary rainbow, caused by interference of
light emerging from large water drops. (NOTE: The supernumerary
bows killed the corpuscular theory of light in the 17th century
because they could only be explained by treating light as a
wave.) The bright inner bow is the primary, and the fainter
outer bow is the secondary (the order of the colors in the secondary
is reversed from the primary). Alexander's Dark Band is the
area between the two rainbows, which is noticably darker than the
surrounding sky. Click on the picture to view these in the
enlarged image.
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Sundog
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Dr. Adam also explained "halos",
circular bright bands that appear 22
degrees from the Sun (due to light scattering from ice crystals),
and "sundogs",
bright colored spots (sort of mini-rainbows) at least 22 degrees from
the Sun in the horizontal plane. Sundogs occur when light reflects
and refracts within flat hexagonal ice crystals oriented horizontally,
and halos occur when light reflects from randomly-oriented ice
crystals.
Dr. Adam showed a series of glorious slides of primary and secondary
rainbows, supernumerary
bows, halos, sundogs, glories,
and sun pillars.
These, and many other atmosheric phenomena, can be seen on the
"SundogUK" link shown below. Be sure to visit all these sites
for more detailed information, and for marvelous images of
atmospheric optical phenomena:
Science and Reason in Hampton Roads (www.ScienceAndReason.org) is an
organization devoted to the critical examination of dubious or
extraordinary claims. It has organized haunted house investigations,
Superstition Celebrations, and talks on topics from UFOs to
alternative medicine.
For more information, contact Larry Weinstein, Professor of Physics
and SRHR President, at 757-683-5803 or at weinstei@physics.odu.edu.
