The Parry Arc
Among reports of peculiar mirages or other strange phenomena observed in the Arctic is one described by P. Berwick of Fairbanks. In that instance several people at a DEW-Line site saw, on two different nights, what appeared to be the lights of a large city on the horizon. Was this a mirage, the northern lights or what?
A possible explanation is the Parry arc named after the explorer, W. E. Parry, who first reported seeing the phenomenon while searching for a northwest passage in 1819-1820. The Parry arc is actually moonlight or sunlight deflected by passing through elongated airborne ice crystals. As the crystals fall, they tend to align themselves with their long axes horizontal. In effect they make many prisms that deflect light by about 22° and spread it out into the colors of the rainbow.
The Parry arc will appear below or above the sun or moon and so can be seen when these celestial bodies are obscured by clouds or the horizon. Its configuration is such that it could, in some circumstances, be mistaken for the lights of a city just on or just over the horizon. The Parry arc is but one of several related phenomena caused by sunlight or moonlight being deflected by airborne water or ice particles.
