When the Moon is shown with a distinct red color or glow. Also called a "blood moon." This is often considered an evil omen.

In real-world astronomy, the Moon turns red during a total lunar eclipse because sunlight is completely blocked by Earth and the only light reflected from its surface has been refracted from Earth's atmosphere, which is red in color for the same reason that a sunrise or sunset turns the sky red. In other words, the only sunlight reaching the Moon is the same sunlight being seen on Earth as sunrise and sunset.