RED sky at night,
Shepherd’s delight;
Red sky in the morning,
Shepherd’s warning.
In the Middle Ages, production of wool and other textiles formed the backbone of the English economy (see Baa, Baa, Black Sheep). Which is why shepherds and their flocks regularly appear in some of our oldest rhymes. Long before twenty-four-hour weather forecasting, country folk relied upon clues from nature to predict forthcoming weather. According to such country lore, birds will build their nests high in the branches of a tree during the spring if their instinct informs them the coming summer will be warm and dry and they therefore don’t need to rely on the shelter afforded by the lower branches. Cows lying down in a meadow are a sure sign of rain as instinct instructs them to keep the ground beneath them dry, while haze around the moon at night is another indication of rain to come. Bees will remain in their hives if a storm is coming, while high-flying swallows indicate warm, dry weather ahead.
In a similar vein, shepherds – who spent all their working day outside and, like farmers in general, needed to be able to predict bad weather as their livelihood depended on it – grew to recognize that when there was a particularly red sunset then the following day would be bright, clear and sunny. However, a red sky at sunrise usually indicated stormy, inclement weather for the day ahead. And it appears that meteorology can back up the folklore. The reason the sky glows red is due to the sun shining on the underside of clouds from a low angle, either at sunrise or sunset. As weather systems generally move from west to east, this reflection would predict, with reasonable accuracy, if rain clouds were moving towards you in the morning or away from you during the night.