What is the origin of “red sky at night, sailors delight; red sky in the morning, sailors warning”?

This saying has very old roots based in the Christian bible from the New Testament. In Chapter 16, verses 2-3 of the gospel of Matthew. One traditional translation reads, “When it is evening, ye say, fair weather; for the heaven is red. And in the morning, foul weather today for the heaven is red and lowering”. A more contemporary translation from the Jerusalem Bible (1966) reads, “In the evening you say, it will be fine; there is a red sky, and in the morning, Stormy weather today; the sky is red and overcast.”

Two scientific factors contribute to the validity of this saying. The first is that weather systems generally travel from west to east in the mid-latitudes. Because the sun rises in the east and sets in the west, a rising sun in advance of an approaching weather system would illuminate the approaching mid-and high-level clouds to create a red sky in the morning.

Alternatively, if the sun is setting as weather systems exits and high pressure is building, then the departing clouds would be illuminated. This would also create a red sky at night with fair weather to follow.

The reddish color results from a scattering of sunlight by suspended particles and aerosols in the atmosphere. The suns rays pass through a greater length of the atmosphere at sunrise and sunset than at any other time of day. In addition, aerosol, dirt, and dust concentrations are maximized in the lowest layers of the atmosphere when the atmosphere is dominated by sinking air.