- 46° halo
A 46° halo is a rare and huge halo, together with the smaller
22° halo a circularoptical phenomenon centred on thesun . At sun elevations between 15-27°, it is often confused with the more colourful and frequently observed supralateral andinfralateral arc s. It is named for crossing theparhelic circle 46° from the sun.46° halos are similar to but much broader and much fainter than 22° halos. They form when sunlight enters randomly oriented
hexagon alice crystal s through a prism face and exits through a hexagonal base.cite web
url = http://www.meteoros.de/arten/ee12e.htm
title = 46°-halo | publisher = Arbeitskreis Meteore e.V.
accessdate = 2007-04-16 | language = English] The 90° inclination between the two faces of the crystals causes the colours of the 46° halo to be more widely dispersed than those of the 22° halo. In addition, as a lot of rays are deflected at larger angles than the angle of minimum deviation, the outer edge of the halo is more diffuse.cite web
url = http://www.atoptics.co.uk/halo/46form.htm
title = 46° Halo Formation | publisher = Atmospheric Optics
accessdate = 2007-04-16 | author = Les Cowley (?) (including an illustration and an animation)]To tell the difference between a 46° halo and the infra-/supralateral arcs, one should carefully observe sun elevation and the fluctuating shapes and orientations of the arcs. The supralateral arc always touches the
circumzenithal arc , while the 46° halo only achieves this when the sun is located 15-27° over the horizon, leaving a gap between the two at other elevations. In contrast, supralateral arcs cannot form when the sun is over 32°, so a halo in the 46°-region is always a 46° halo at higher elevations. If the sun is nearzenith , however, circumhorizontal orinfralateral arc s are located 46° under the sun and can be confused with the 46° halo.cite web
url = http://www.atoptics.co.uk/halo/46orsup.htm
title = Is it a 46° halo or a supra/infralateral arc? | publisher = Atmospheric Optics
accessdate = 2007-04-16 | author = Les Cowley (?)] cite web
url = http://www.meteoros.de/arten/ee21e.htm
title = Supralateral arc | publisher = Arbeitskreis Meteore e.V.
accessdate = 2007-04-16 | language = English]See also
*
Circumzenithal arc
*Tangent arc References
External links
* [http://www.atoptics.co.uk/halo/46hal.htm Atmospheric Optics - 46° Radius Halo] - including a
HaloSim computer simulation and an Antarctica fish eye photo.
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