NASA says December 21 this year is just the winter solstice not the end of the world.

According to believers, the world will undergo a major transformation later this month, as the ancient Mayan Long Count calender comes to the end of its 13th cycle. Some say it will be the end of the world, perhaps via a collision with another planet or a black hole, while others claim there will be some kind of spiritual awakening, the effects of which depend on who you ask.

But according to NASA, there is nothing special about December 21, 2012, and there's definitely nothing to worry about.

In a post on their website, NASA says the planet has been "getting along just fine for more than 4 billion years, and credible scientists worldwide know of no threat associated with 2012".

"Just as the calendar you have on your kitchen wall does not cease to exist after December 31, the Mayan calendar does not cease to exist on December 21, 2012. This date is the end of the Mayan long-count period but then - just as your calendar begins again on January 1 - another long-count period begins for the Mayan calendar."

NASA says claims that a planet named 'Nibiru' or 'Planet X' will hit the Earth, like in the Lars von Trier film Melancholia, are an "internet hoax".

"If Nibiru or Planet X were real and headed for an encounter with the Earth in 2012, astronomers would have been tracking it for at least the past decade, and it would be visible by now to the naked eye."

Another planet mentioned in conspiracy circles is Eris, which although real, never comes closer than 6 billion kilometres away.

Some say Earth's rotation will reverse, but NASA says this is impossible.

"There are slow movements of the continents (for example Antarctica was near the equator hundreds of millions of years ago), but that is irrelevant to claims of reversal of the rotational poles."

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NASA: December 21 theory an 'internet hoax'