I guess it depends on whether we decide a) the dark spots are holes in the ?higher layer of cirrus or b) shadows cast on that layer by the white puffs (which COULD be above the cirrus and show through as more intense white if the cirrus is thin enough) or c) shadowed sides on the dense puffs on their side away from the sun. In c) the sun's position & strength would obviously be crucial. Just goes to show how the sky gives us intriguing puzzles to solve all the time - great free entertainment! Even if we were there at the time and could see the whole scene in 3 dimensions, we'd still have difficulty figuring out exatcly what is going on
Any more guesses folks? GWW
