Historically humans have considered very bright comets - especially those visible in the daytime - to be omens, and usually of doom. These heavenly portents would precede war, famine, earthquakes... all the usual harbingers of the yet-to-arrive apocalypse. On some level you can't blame people from the past; can you imagine waking up one day and seeing a huge bright star with a long tail suddenly floating in the sky? That's some freaky shit, and without proper astronomy they couldn't really understand what was going on.
Now we do. We know that comets are balls of ice - thought to be usually found in the hypothetical Oort Cloud, located just outside our solar system - that get caught up in the sun's (or Jupiter's) gravity and begin a crazy trip through the solar system. The comet's tail is caused by solar radiation vaporizing the object, sending out a streamer behind it. Comet is derived from the Latin word comete, which means 'long haired.' Aristotle called them 'Stars with hair.' And we now have enough understanding of physics to be able to chart a comet's course while it's still a long, long way out.
Enter Comet ISON. First discovered in 2011, ISON is a course that will bring it very close to Earth, after which it will essentially scrape the sun and, should it survive that encounter, will come rocketing back past us again. Along the way it will be incredibly bright - possibly as bright as the full moon! - and will on November 28th be visible in the daytime. This will be only the tenth time in recorded history that a comet will be visible in the daytime.
ISON will graze the surface of the sun; at this point it may either be destroyed or will come around the other side smaller, but slingshotted away at a high rate of speed. It may be a shattered mess, or like 2011's Comet Lovejoy it may be smaller but still intact. If it does survive, it'll get really interesting. From Space.com:
As ISON slows its course and recedes back out into space, the comet will now be buffeted at close range by the solar wind, driving particles from the comet’s head (called the coma) out into a long stream preceding the comet.
The result? A tail, stretching perhaps for tens of millions of miles, might protrude from above the horizon like some ghostly searchlight beam. And while it will be moving away from the sun, ISON will now be approaching Earth, passing closest to us on the day after Christmas, vaulting over our planet at a distance of 39.6 million miles (63.7 million km).
By then the comet will be a circumpolar object for those in north temperate latitudes, neither rising nor setting, but instead remaining perpetually above the horizon all through the night!
Some astronomers think ISON may actually be 'The Great Comet,' a comet viewed in 1680 and the very first comet ever seen through a telescope. That's pretty cool.
So it'll be a highly, historically visible comet in the night sky right at Christmas? That can't possible be twisted into some kind of meaning by superstitious religious types, could it? We like to imagine that we're much more advanced than the poor pre-telescope suckers, but remember back to Comet Hale-Bopp, whose approach led to the Heaven's Gate suicides. Could Comet ISON be the spark for similar delusional deaths? I wouldn't be surprised. And I wouldn't be surprised if we start hearing all sorts of doomsday talk, Anti-Christ talk and other craziness.
I don't know that we're living in the End Times, but we might be living in the Dumb Times.