system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Red sky at night, sailors delight. Red sky in the morning, sailor's warning.
gpt
It's related to the fact that the Sun sets in the West and rises in the East, and that most weather in the mid-latitudes (especially around Europe) where the traditional sailing routes are tends to move from West to East.

In order to get a red sky, two things need to happen.  There need to be water-laden clouds (which appear red when lit from their underside), and there needs to be clear skies over the horizon so the sun can light the underside of the clouds closer to you.

If there is a red sky at night, that means there are clear skies to the West, so the approaching weather will be clear.

If there is a red sky in the morning, that means there are clear skies to the East, but the sky closer to you is filled with clouds.  And since the high pressure system (the clear skies to the East) has already passed, it's likely those clouds are going to be followed by more clouds from the West.