Can anyone explain the pattern seen here in the sky (see photo)? It was spotted in the Pyrenees at about 8 am. We were heading east and although it gradually faded, it lasted for some time. The mountain pass over which the light is shining is at an altitude of 2000 metres and there is nothing in the next valley or mountain that could explain the pattern.
鈥� Your correspondent has captured a rare version of the poet Homer鈥檚 鈥渞osy-fingered dawn鈥�. Here, however, the 鈥渇ingers鈥� are actually shadows separating columns of sunlit air.
The scientific name for this pattern of sunlight is crepuscular rays. In the photographed case the sunbeams are wide and are virtually invisible in the clear dawn air. Only the background of the and the much lower shadowy mountains reveal them.
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Extending the lines of the shadows down to a point gives the position of the sun: very low behind the ridge. Your reader says there was nothing to explain the pattern in the terrain behind the ridge, but sometimes this type of shadow can be cast from an object many dozens of kilometres away 鈥� perhaps the crenellations on a distant parallel ridge.
鈥淓xtending the lines of the shadows down to a point gives the position of the sun: low behind the ridge鈥�
However, the shadows are so evenly spaced that I would guess the culprit is a distant line of , or .
The shadows gradually fade as the sun rises in the sky, or when the clouds drift in a high-level wind.
A superb website sharing hundreds of atmospheric phenomena is Atmospheric optics, at . Even anti-crepuscular rays can be seen. Enjoy!
Frank Goodman, Nottingham, UK
鈥� These crepuscular rays are shafts of sunlight that radiate from a point in the sky where the sun is located, which is sometimes below the horizon.
The shafts are formed when the sunlight passes through gaps in cloud. In this photograph the gaps are hidden from view by the mountain. The sun is so far away that these rays of light are actually parallel but perspective means they appear to converge on a point, in the same way as do verges of a road.
The word crepuscular is derived from the Latin crepusculum, meaning twilight, so they can appear at sunset as well as sunrise. At this time of day sunlight has to pass through more air, as the sun is sitting on or near the horizon. This means that more blue light is scattered out of the beam and explains why crepuscular rays are often yellow or red, making them conspicuous against a dark dawn or dusk sky. Crepuscular rays are sometimes known as a sunburst or a Jacob鈥檚 ladder.
Mike Follows, Sutton Coldfield, West Midlands
This article appeared in print under the headline 鈥淔ingers of Sol鈥�