Eclipses glossary
What is a Blood Moon?
Blood Moon is a popular name for the reddish Moon seen during a total lunar eclipse, when sunlight filtered through Earth's atmosphere reaches the lunar surface.
What it means
Blood Moon is part of eclipse geometry and timing. Eclipses require the Sun, Earth, and Moon to align near the points where the Moon's tilted orbit crosses the ecliptic. That tilt is why an eclipse does not occur at every new or full Moon.
For a deeper look with practical observing advice, read the Moonrise Moment guide to blood moon.
Sources and further reading
This definition was written in plain language and checked against these science references.