Tangent Arcs above Lake Balaton
Atmospheric halos and arcs appear around the Moon in this winter view from Lake Balaton, Hungary. Known as 22-degree halo, its a common atmospheric phenomena around the sun or the moon, specially in regions with cold temperatures. But this view also displays a bright upper tangent arc and a lower tangent arc. These arcs are atmospheric optical phenomenon which appears tangent to the 22° halo around the sun or the moon. The tangent arc form when hexagonal rod-shaped ice crystals in cirrus clouds have their long axis oriented horizontally, while otherwise rotated in any direction. This orientation of the crystals also produces 22° halos and sun/moon dogs, but a predominant horizontal orientation is required to produce a crisp tangent arc, as recorded in this image.