by Ern Mainka (photography
site) in Australia 25th March '08. Image ©Ern
Rainbows are actually disks of light brighter at their edges. The disks
of each colour overlap but are of different sizes and hence we see their
coloured edges - they are the bow.
The disks are
centred on the antisolar point directly oppositie the sun and this is
also where shadows converge by perspective.
The dark parts of the 'spokes' are where raindrops are shadowed
by clouds and are therefore unable to glint light and contribute
to the light of the disk. The spokes
are related to - but not the same as - anticrepuscular rays