Setting Moon in a red sky. Gibbous Moon setting in a red sky over the island of Milos, north of Crete in the Mediterranean Sea. This view was seen from the island of Santorini. Gibbous refers to the phases of the lunar cycle where more than half of the visible side of the Moon is lit up by the Sun. A red sky at night (at or near sunset) usually indicates fair weather to follow the next day.