Since the beginning of civilization, humans have used the clouds, the wind, the appearance of the sky, and the smell or feel of the air to help them predict the weather. There are a variety of old adages, known as weather lore, that have been passed down through the generations and, while some have no scientific basis, the rhyme, “Red skies at night, sailor’s delight. Red skies in the morning, sailors take warning,” actually holds a fair amount of truth.
Scientific explanations for the red skies
In the United States and the United Kingdom, the weather normally runs in a west to east direction. Storm systems usually develop in the west and the Westerly trade winds are responsible for moving them towards the east.
During sunrise and sunset, the sun’s rays pass through the atmosphere at a very low angle forcing the light to shine on the underside of any existing cloud cover. Due to the thickness of the atmosphere at this angle, the shorter wavelengths of the spectrum, the blues, greens and violets, are scattered, and allow the longer, red rays to remain visible, hence the infamous evening and morning red skies.
At sunset
High-pressure systems in the west help to refract the sun’s light waves even more, causing the air to sink as more dust and smoke particles are trapped and held closer to the earth. The sun’s rays have an unobstructed path from the west and are illuminating the underside of the potential storm clouds that are involved in the lower pressure system moving towards the east. This produces clearing skies in the west and results in a red sky at sunset.
At sunrise:
Low-pressure systems occur from rising air and are responsible for producing more clouds and potential precipitation. So, high-pressure systems in the east mean that lower pressures are in the west. The clear skies are now off to the east, while the clouds in the west are receiving the underside illumination of the rays and produce a red sky in the morning.
References to the red sky phenomena also appear in various texts, including the Bible: Matthew 16:2-3
Jesus replied,
“When evening comes, you say,
it will be fair weather: for the sky is red.
And in the morning,
it will be stormy, for the sky is red and overcast.”
And in Shakespeare’s poem, “Venus and Adonis:”
“Like a red morn that ever yet betokened,
Wreck to the seaman, tempest to the field,
Sorrow to the shepherds, woe unto the birds,
Gusts and foul flaws to herdmen and to herds.”
The ability to predict weather through the observation of a red sunset or sunrise appears to be more fact than fiction.
