Blood moons, one from Colorado (USA), and the other from Switzerland. (Click on the images to see them full-size.)

The term "blood moon" relates to the reddish color of a totally eclipsed Moon. During a total lunar eclipse (when the moon moves completely behind the Earth vis-a-vis the sun), the gray full moon begins to slowly turns red, displaying ever-changing reddish, pinkish and orange hues for a short while, and then slowly returning back to normal grey as it comes out of the Earth's shadow.

The reddish colour of the eclipsed moon comes about because the rays from the sun are able to wrap around the Earth from one side to the other, reaching the moon in this roundabout way and reflecting off it. However as the green to violet wavelengths of the sun's rays scatter more strongly than the red, the eclipsed moon obtains a reddish cast.