Behind the folklore: red sky at night: Is red sky delightful for shepherds?

Behind the folklore: red sky at night: Is red sky delightful for shepherds?

Fri, 16/07/2010 - 11:21
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Red sky at night, shepherds' (or sailors') delight

Red sky in the morning, shepherds' (or sailors') warning

Other than the prolonged absence of female company, there hasn't been much that has united shepherds and sailors throughout history. But if the two most common forms of this age-old rhyme are to be believed, a mutual love of nocturnal red skies and antipathy towards red-tinged mornings binds these two ancient professions together.

The rhyme certainly has some fairly heavyweight credentials, with the Gospels and William Shakespeare offering early support. The impact of red skies is first mooted in Matthew 16, with Jesus telling the Pharisees:

""When it is evening, ye say, it will be fair weather: for the sky is red. And in the morning, it will be foul weather to day: for the sky is red and lowring.""

Shakespeare, who used the weather as a plot development device even more frequently than cross dressing and twins, was the first to mention sailors and shepherds together in this context, in his 1593 narrative poem Venus & Adonis:

""Like a red morn, that ever yet betoken'd
Wrack to the seaman, tempest to the field,
Sorrow to shepherds, woe unto the birds,
Gusts and foul flaws to herdmen and to herds.""

With both the Messiah and the Bard of Avon backing it up, this is clearly no ordinary piece of hokey folk wisdom. But is there any science behind it?

The simple answer is ""yes"". To a degree.

Red skies occur when the sun is low in the sky and sunlight is scattered by suspended particles in the atmosphere. Most weather systems that impact on the UK travel from west to east, blown by the prevailing winds. As the sun rises in the east and sets in the west, if a weather system is heading towards us in the morning, the low sun will illuminate the approaching clouds, creating a red sky. If the sun is setting as a weather system exits to dump its watery load on somebody else, then the departing clouds will be illuminated. The resulting nocturnal red sky suggests that the system has passed and fair weather will follow.

This doesn't always work. For a start, not all weather systems travel west to east. And more importantly, just because one weather system has just passed, that doesn't mean that another of the soggy blighters isn't following firm on its tail. Still, as far as folklore goes, this particular piece does stand up to scrutiny. Shakespeare and Jesus, go to the top of the class.