This evening's "blood moon" will be the longest total lunar eclipse until 2123.
It has been calculated to last for an hour and 43 minutes, while the entire eclipse (including the partial phases) will last for more than six hours.
Check out AOL News's Five Reasons Why This Week's Lunar Eclipse Is Going To Be A Rare Celestial Delight for a simple overview of the facts.
The Telegraph has some factoids as well.
But enough of the science bits, how can we use this real world spectacle in our RPGs?
Thankfully, the usual crop of doomsday nutters have crawled out of the woodwork to kick things off with their idiotic, apocalyptic, jibber-jabber.
The great thing about baseless prophecies is that they work in pretty much every RPG setting imaginable from fantasy to sci-fi, superheroes to swashbucklers. I can even imagine "doomsday cults" in games as diverse as Paranoia and My Little Pony.
The moon is a major factor in a lot of supernatural mythologies, and we all know its effect on werewolves... but what extra impact would a blood moon have? Particularly a prolonged one like this?
Were the Mayans right? Is something monstrous eating the moon?
Perhaps a major antagonist needs the light of the blood moon to cast a particularly powerful spell? Or a major powercut in your heroes' city incites an impromptu Purge Night of looting and violence under the reddish hue of the blood moon?