MIAMI (CBSMiami) – Depending on who you choose to believe, Friday will either be the end of the world as we know it, or it will simply be the beginning of the last weekend before Christmas.

December 21 is the end of a 5,125 year-old Mayan calendar, which some interpret as the “end of days” for Earth. However, it should be noted the Mayan calendar continues after December 21, 2012; that fundamentally undercuts the end of days prediction.

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Technically, according to Reuters, Friday marks the end of the 13th bak’tun, which according to the Maya Long Count calendar is an epoch lasting roughly 400 years. Friday will also mark the beginning of the 14th bak’tun.

Nevertheless, the predictions have taken hold in cultures around the world and have spawned an entire industry of people selling predictions the world would end. From people claiming Nostradamus has predicted a similar date, to fears of an alignment in the universe, to solar storms, there’s been no shortage of potential end of the world events predicted for Friday.

NASA went so far as to create websites dedicated to debunking the apocalyptic rumors for December 21 2012. As for planetary alignments, NASA said none are set to happen in the next few decades, and even if they did the effects would be negligible.

NASA also said the Earth and sun align with the center of the Milky Way Galaxy each December, but that’s an annual event of no consequence. NASA also said the solar storm theory is bunk because the next solar maximum is between 2012-2014 and expected to be an average cycle.

Still, around the world, believers are gathering in Mexico for the Mayan apocalypse while others are gathering in a mountainous French city to meet up with aliens.

Apocalyptic predictions are nothing new in history: from Christianity to Islam to nearly every other religion and culture, each has its own theory on how the end of days will occur. The toughest element, of course, is determining the exact time.

As far back as the 11th Century, some Christians believed the 1,000 year anniversary of Jesus’ death would bring about his second coming and the end of days predicted in the book of Revelation. In the 14th century, the black plague was believed to be God’s judgment on the world and the beginning of the end times.

The predictions gain momentum at different points in time; for example at the turn of a century and at the turn of the millennium, remember Y2K? The 2012 apocalyptic prediction reaches its climax on Friday, but is likely to suffer the same fate as many other apocalyptic visions.

There are countless examples of recent apocalyptic predictions not exactly going as planned.

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Just last year, Harold Camping and his followers predicted the world would end on May 21, 2011. When May 22 came around, Camping blamed the mistake on a mathematical error and moved the date of the end of the world to October 21, 2011, which obviously also came and went.

One of the most infamous groups to fail with the end of days predictions was William Miller and his followers, known as Millerites. Miller said Jesus would return in March 21, 1843 and barnstormed the nation with his message saying he derived his prophecy from mathematical calculations.

As March 21, 1843 rolled around, around 100,000 of his followers sold all of their possessions and began waiting for the rapture of the church to begin. On March 22, Miller said the date was recalculated to March 21, 1844 and then October 21, 1844. Both dates were a swing and a miss by Miller.

Miller’s failure was nicknamed “The Great Disappointment.”

In May 1910, Halley’s Comet was at the focus of a doomsday prediction, one that called for poisonous cyanogen gas in the comet’s tail to generate widespread death on Earth. This prompted some to fear the end of the world and try to protect themselves from the “problems.”

Pat Robertson, the leader of the “700 Club” broadcast, said October/November 1982 was the official beginning of the end times. Robertson made the initial prediction in the late 1970’s and stuck with it throughout 1982.

Even in 2009, some physicists were claiming there was an extremely remote chance that a black hole could be created when the Large Hadron Collider was started. The black hole would then consume the planet. The LHC has been turned on a recently may have discovered the Higgs-Boson, also known as the God Particle.

Eventually, scientists admit, the Earth will end, most likely because of the sun. In a few billion years, the sun will become a red giant and as that process continues, all bets for life on Earth are off.

But, barring a major failure by science or something else completely unexpected, December 21, 2012 will come and go just like every day before it and the days after it, the Mayan calendar will turn over to the next bak’tun, and there may be some very disappointed people around the world.

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We’ll all know the outcome in less than 12 hours, when the clock strikes midnight on 12/21/2012, at least in the Eastern Time Zone. (FYI: It’s already 12/21/12 on the other side of the world, and everything is still spinning)