Red sky at night
Where would the British be without their weather?
The sheer variability of the climate, rarely the same one day after the next and often a combination of rain, wind and sun all in one day, provides us with an inexhaustible subject for conversation. Modern life is not so dependent upon the vagaries of the weather. Of course it is irritating to be out without a coat or umbrella and find what was a nice, bright day has turned wet and a long-term commitment to an outdoor event requires the sort of steely determination that only the Brits can muster.
But in days of yore, when many sources of earning your living and/or your safety was dependent upon climatic conditions, it was useful to have some sort of system to work out what sort of weather you were in store for the following day. Our rhyme purported to do that. There are two variants. The one I am most familiar with goes, “red sky at night, shepherd’s delight/red sky at morning, shepherd’s warning”. The other variant replaces the land based shepherd with a sailor.
I remember as a child being excited if the sky was red at sunset and disappointed when the red glow appeared in the morning. But is there anything to it and where did it come from?
The latter question is easiest to answer. Wycliffe’s translation of Matthew 16: 2b – 3 in 1353 has Jesus saying, “when it is evening, you say it will be fair weather for the sky is red/ and in the morning, it will be foul weather today, for the sky is red and lowering./ O ye hypocrites, ye can discern the face of the sky, but can ye not discern the sign of the times”. Shakespeare picks up the theme in Venus and Adonis (1593), “like a red morn that ever yet betokened/ wreck to the seamen, tempest to the field/ sorrow to the shepherd..”
To establish whether there is any truth in the rhyme we need to understand how sunlight travels through the atmosphere. We are familiar with the spectrum of colours we see in a rainbow and sunlight when it travels through the atmosphere breaks up into that range. The blue and violet elements of the light are more diverted than the red and orange colours which is why during the day, if we are lucky, the sky seems broadly to be of a blue colour. But when the sun is low, at dusk and dawn, more light travels through the atmosphere and the red and orange colours are better able to go directly towards and be reflected from the clouds when pressure is high. Hence the red hue of our rhyme.
In England our weather system comes predominantly from the west. So when we see a red sky at sunset it means that high pressure is coming from the west which is generally indicative of a dry and pleasant day to come. Conversely, if the sky appears red in the morning it means that the high pressure weather system has already moved eastwards and what we are left with is a wet and windy low pressure system.
So, broadly speaking, there is some truth in the canard, provided, of course, your weather system is broadly westerly based. Otherwise , it is as useful as a chocolate teapot.