The Potomac in the clouds imaged in Virginia by Ken Musgrave. ©Ken Musgrave , shown with permission.

The blurred bright shape on the cloud underside at left is a partial map of the Potomac River. Ken Musgrave vowed that some day he would capture a complete one.

Sunlight striking the river and landscape is scattered back upwards to light the cloud. The water scatters and reflects more light. Its multiply curved surface acts as mirror reflectors. 'Reflection' is a term reserved for light scattering from large surfaces that are smooth compared to light's wavelength like polished metals and liquid surfaces..

Eskimos were said to have used similar sky maps - ice blinks - produced by sunlight scattered from ice floes and icefields.

Sometimes, in less frozen lands, fields of brightly coloured crops can be located by their light scattered onto low clouds.