Large Nature, Tiny Artifact - Circumhorizon arc, Pilesgrove, New Jersey imaged July 22, 2007 by Lisa Gonnelli.

Circumhorizon arcs are so huge that their colours sometimes appear to be those of the sky itself rather than an ice crystal halo. In this long-lens shot the halo forms a backdrop to a seemingly tiny aircraft.

Not all bright arcs below a high summer sun are circumhorizons. They could be infralateral arcs or - much less likely - parts of a 46 degree halo. It can take the sighting of an almost complete arc and careful measurement to distinguish between the possibilities. This one, taking account of other halos in the sky and other local sightings, is most probably a circumhorizon but an infralateral arc cannot be totally ruled out.

Image ©Lisa Gonnelli, shown with permission.