Toronto Halos

An impressive display captured by Xuan Zhang.

At top is an immensely bright 120° parhelion crossed by the parhelic circle.

 All images ©Xuan Zhang, shown with permission
Aficionados of the UofT campus (and of halos) will want to scroll this large panorama to the right.

The projection nicely portrays the parhelic circle as parallel to the horizon.

Note the elusive 'blue spot' on the parhelic circle to the left of the left hand 120° parhelion and to the right of the RH one. This is where total internal reflection ceases, first for red rays and then for blue.
Atmospheric
Optics
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Plate crystals dominate. They generated most of the intensity of the parhelic circle, they produced the 22° and 120° parhelia and the circumzenithal arc overhead.

Randomly oriented hexagonal prisms of some kind made the 22 degree halo and the 46° halo fragment (it could instead be a supralateral arc). Horizontal columns were in the minority giving a weak and indistinct upper tangent arc.
   
   
120° parhelion

Plate crystals with their large hexagonal faces nearly horizontal yielded the amazingly bright 120° parhelia on the parhelic circle.

In one possible ray path sunlight enters a top face, internally reflects twice and leaves through the lower face. The entrance and exit angles are equal and there is no net dispersion into colours - the 120° parhelion, unlike the 22° parhelion, is white.

Bright 120° parhelia need thick plates or ones of triangular aspect 9alternate long and short side faces).