blood moon

plural blood moons

1. figurativelyastronomyThe moon as it appears during a total lunar eclipse.

   Just after two o'clock in the morning, the moon went into eclipse, fading to a deep red and casting a pall over the mountainside. Viewing the blood moon as an ominous sign, the Confederates used it to cloak their flight.

   2006, Georgiana Kotarski, Ghosts of the Southern Tennessee Valley, →ISBN, pages 98–99

   2 more examples

   “Because the Earth has an atmosphere, it doesn’t completely block the light on the moon. Some of the red light actually bends through the Earth’s atmosphere and lights up the moon during a total eclipse, and that’s the rusty red, blood moon,” said SubbaRao.

   2014, Gaynor Hall, “Blood Moon Rising: Chicago star gazers in for treat if weather holds out”, in WGNtv.com, retrieved 15 Apr 2014

   Sky gazers in India and in other parts of the world will be able to witness a blood moon on September 7 during a total lunar eclipse. The moon will take on a dark red-copper hue. This is the result of a physical effect called Rayleigh scattering. During a total lunar eclipse, the earth comes between the sun and the moon, blocking direct sunlight from striking the lunar surface. However, not all sunlight is blocked. Only the bluer light is filtered out; the redder light is scattered by the earth's atmosphere, giving the moon its striking colour.

   2025 September 6, Priyali Prakash, “Why is a blood moon called so? Sky gazers in India will see a blood moon on September 7 during a total lunar eclipse”, in The Hindu