Circumscribed arcs or upper tangential arcs, are another sky phenomenon that are hard 
to locate. They will develop across the top of the sun halo, with the ends curving 
upward. They require the thin, nearly transparent cirrostratus clouds, and horizontally 
orientated 'pencil-shaped' ice crystals to refract the sunlight. Usually, the colder 
the air, the more intense the arc definition will be.

  A pair of glasses with polarized lenses is required, not only to protect the eyes,
but most of these sky phenomenon can't be detected without them!

  I have noticed the form of the upper tangential arc changes its shape according to the
position of the sun. The higher the suns position in the sky, the more the arc looks
like a moustache. As the suns position sinks lower, the arc looses its 'handlebars', and
starts to turn upward to finally end in a tight 'V' formation.

uppertangarc11703

uppertanarc92602

circumscribed arc

upprtang42002b

upprtang42002

Back To Firmament Picks

All photos available for sale at: 'universed2@i-is.com'
All photos are copyrighted. No use or duplicating without written permission.