It’s a familiar old rhyme that we don’t take much stock in any more: “Red sky at night, sailors’ delight; red sky at morning, sailors take warning.” But, for an age before satellite imaging, the rhyme contained some solid meteorological truth. The red sky mentioned is not just sunset or sunrise. As the sun rises in the east, if the sky around it is clear enough for its rays to reach the clouds in the west, it makes them glow red. That combination of clear and cloudy sky suggests that a weather front is moving through. Since most storm systems move from west to east, a red sky at morning shows clouds moving in from the west, while red sky at night is the result of clouds rolling safely away into the east.