Crepuscular rays
Image Index          Upward crepuscular rays from spring cumulus.  The clouds are dark grey because little light penetrates them. Some have brilliant "silver linings". When clouds are backlit, water droplets in the thinner regions around their edges scatter light forwards very efficiently. This light which is brighter by contrast with the darker shadowed parts forms the silver lining. Cumulus clouds have the finest 'linings'.     �Les Cowley