In a sight like this it is hard to believe that the sun�s rays are not spreading outwards in all directions. They are not, it is a perspective effect.

Where the sun shines through gaps in the clouds it produces parallel (and always downward going) shafts of sunlit air. Change the mental picture next time you see them by visualising them as slanting rods passing from the clouds to the ground. Apparently upward going rays are ones that, if continued, would pass over your head as they slope ever downwards.

Sunrays are one of the few atmospheric optics effects that are real in the sense that it is possible to walk or fly around them and view them from different angles.

The image shows another perspective effect � aerial perspective much used by artists. The hills look progressively lighter and pastel hued as they recede into the distance. �Airlight�, scattered light from air molecules, aerosol and dust in the intervening atmosphere is responsible.