Did you enjoy those beautiful sunsets in many parts of the country last week? They will not be so good this week, I fear. And it's all because a red sky at night really is a shepherd's delight. It's one of the more justified of the old wives' weather tales.

It's all because of the path taken by the sun's rays through the atmosphere on their way to earth. Sunlight is scattered by both air molecules and dust particles. The air molecules scatter the shorter wavelengths of light - which accounts for the usual blue appearance of the sky - while the considerably larger dust particles scatter the longer, red wavelengths.

During the day, the sunlight shines straight through the atmosphere, but in the evening, when the sun is low in the sky, its light hits the atmosphere obliquely and has a longer path through it, encountering considerably more red-scattering dust, than during the day.

But you will see the redness only if the sky is clear and dry for a long distance to the west. And since most of our weather comes from the west (because of the prevailing westerlies, which result from the earth's rotation and the Coriolis force, which we shall discuss when it is little windier) that means we're in for some clear skies. A red sky in the morning tells us only that the sky is clear to the east, which is often the sign of a clear patch between two depressions. When one Low passes, another is often close behind - just look at the recent progress of Lows O, P and E on the weather map. Result: rain, and anxious shepherds.