Every couple of years, the moon slowly goes dark before taking on a bloody pallor colloquially known as a blood moon, but what causes it to turn red?

Lunar eclipses happen during the full moon phase, when Earth moves directly between the sun and the moon. This alignment causes Earth’s shadow to fall on the moon, gradually dimming its surface, NASA reports. During a total lunar eclipse, the moon passes through the darkest part of Earth’s shadow, known as the umbra.