According to popular lore, you can predict the weather based on sky color. The saying typically goes, “Red sky at night, sailor's delight. Red sky at morning, sailors take warning.” This saying has been around in various forms for a long time — there’s even a version of it in the Bible. The reason it’s lasted so long is that it actually works, at least in certain parts of the world. In the temperate zones, weather systems generally move from west to east. Because of the curve of the Earth and the haze of the atmosphere, you can’t see the clouds to your west. The “red sky” trick gets around this by using the sun. Red wavelengths pass through the air more easily than blue ones. When the sun is setting in the west, its light passes through hundreds of miles of atmosphere — becoming extremely red in the process — before hitting the clouds above you. If there are storm clouds to your west, the red sunlight is stopped before it can get to you, and the sunset doesn’t look particularly red.

Source: New York Times