These are some pictures showing optical effects caused by our atmosphere.1999 Aug-early Sept: a circumzenithal arc [below] seen in cirrus on three additional afternoons in this period from 5.00pm to 5.30pm above a lowish sun.....it must be fairly common.
1999 Aug 5: My first view of a colourful circumzenithal arc - recorded from my garden on the Kodak DC 40 camera. They are centred on the zenith and formed with the sun 46o below the 'bow' and the sun <32o above horizon [ref:Clouds of the World by Richard Scorer].
1999 July 3 - midnight: Strong evidence of Noctilucent Cloud on northern horizon below and west [left] of Capella as a pearly blue light like horizontal wisps of cirrus cloud. No movement detected in 15 minutes. Seen through breaks in silhouetted foreground cloud.
1999 June 25 - a quite remarkable day in terms of clarity of the atmosphere coloured a deep blue and completely free of cloud or haze from dawn to dusk. Airplane trails frequently criss-cross the Surrey skies on clear days but were absent today - vapour trails dispersed a degree of so behind a plane - the belly of which were unusually dark or grey [normally they appear white with reflected light from ground haze]. Venus spotted at 4PM as a clear bright star on the meridian to the naked-eye at 50o altitude. The spectrum and disk of Mercury and Venus recorded in full sunlight via the Meade SCT. The sun was painfully brilliant at sunset.
The prismatic refraction of the Earth's atmosphere recorded here in spectrograms of Sirius and Mercury rising in the southeast - bending the image upwards and acting in effect as a cross-disperser. This demonstrates why high resolution planetary images [for example] appear sharper when recorded via a deep [like RGB] colour filter which isolate the various coloured images elevated to slightly different altitudes in the sky. The late Horace Dall designed an adjustable prismatic wedge to nullify the effects of atmospheric refraction.
