A 22° halo from the equator
This photo of the 22° halo around the sun was shot by Frank Starmer on January 22, 2011 on the island of Bintan in Indonesia. The location is Telubakau, Kepulauan Riau, Indonesia. The photo was shot just after sunrise at about 7am local time. It was shot at f8 and 1/1000 sec with a 70-300mm Nikon lens. The location is only one degree away from the Equator. It is remarkable that this phenomenon, which involves refraction in ice crystals, can be seen at the Equator. (Photo used by permission, all rights reserved to Frank.)
One would expect that the halo is caused by very high altitude ice crystals. The familiar 22° halo around the Sun or Moon occurs because of refraction in tiny hexagonal ice crystals in the air. With the 60° apex angle of the prism formed by extending the sides of the crystal and the index of refraction of ice (n=1.31) one can calculate the angle of minium deviation to be 21.84°. |
 |
The presence of a definitely visible parhelion or "sun dog" on a line horizontal from the sun suggests flat hexagonal ice crystals, but the visibility of the entire halo suggests small ice crystals at all orientations.  This is a GPS track of the journey from Singapore to the southeast coast of Bintan where the photo was taken. |  |
| Origin of "sundogs" | Other halo phenomena |
| Moon halo |
Halo formation
Atmospheric optics concepts
References
Greenler
Schaaf
| HyperPhysics***** Light and Vision | R Nave |