What is a blood moon?

In astronomy, the term blood moon refers to a complete lunar eclipse which causes the moon to appear red. The moon looks red due to dispersed light from Earth's sunrises and sunsets that is refracted back onto the moon's surface.

Different atmospheric conditions during an eclipse, including humidity, dust, temperature and more, can make the blood moon vary in color, from a more coppery hue to a deep red. In folklore, the term hunter's moon is also sometimes used interchangeably with the term blood moon. This blood moon refers to a specific full moon, however, which occurs after the harvest moon and the autumn equinox, usually in October.