WHat really is supposed to happen on the year 2012 dec 21st ?

Nope.

The "2012 doomsday" is a hoax. It's a fraud. It's a con job. It's a cruel and cynical lie being promoted by unscrupulous pseudo-scientific cranks who have a monetary interest: They want to sell their books, videos, 'survival kits', and spaces in non-existent shelters in Antarctica. They also want to divert attention from the fact that they have been wrong so many times before. It's also being pushed by people who are promoting a Hollywood disaster movie due out later this year.

All of the claims of 'predictions' by the Maya, the Aztecs, the Chinese (I Ching), Nostradamus, Sir Isaac Newton, Edgar Cacey, "Mother Shipton" are false: they did not make the claimed predictions. Predictions by others such as José Argüelles, Terrence McKenna, Nancy Leider, Mark Hazelwood and others are contrived pseudo-scientific nonsense.

There is no "Planet X" or Nibiru. If someone claims that this object exists, then I (and others in this forum) have been asking for the RA/Dec coordinates for it. If they can provide those coordinates and allow independent verification of its existence, then they can collect $5,000 from http://nibiruchallenge.blogspot.com./ The claim that it is not visible yet, or that it can only be seen from Antarctica is a red herring.

There will be no 'pole shift', either geographic or magnetic. There will be no 'killer solar flares'. These events are fiction. There will be no 'galactic alignment' or 'planetary alignment' of any kind, and we will not pass through the central plane of the galaxy, and even if these events were to occur, they would not cause any problems for us.

As far as what is *really* going to happen:

Olympic games in London

Leap Year

U.S. Presidential election

Transit of Venus on June 6th

Disclaimer: Due to the number of "2012" questions on Yahoo! Answers, this is a cut-and-paste answer. Please see my complete (long) opinion in the link below. After reading that link, if you have additional questions, please leave a comment and I will reply shortly:

http://astrogeek.wordpress.com/hoax/

All the so-called “Mayan prophecies of 2012” are nothing more than wildly speculative extrapolations, which are based on the yet uncertain interpretations by scholars of Mayan hieroglyphs. However, the truth is that apart from the astrological convergence, there is little indication that the Mayans prophesied anything specific regarding the events of this distant future. The Mayans were not prophets; they were not even able to predict their own cultural extinction. They were great mathematicians and accomplished sky watchers, but they were also a brutally violent tribal people with a primitive understanding of natural phenomena, subscribing to archaic beliefs and the barbaric practices of blood-letting and human sacrifice.

There is absolutely nothing in the Bible that would present December 21, 2012, as the end of the world. While that date is no less valid for an end-times event than any other future date, the Bible nowhere presents the astronomical phenomena the Mayans pointed to as a sign of the end times. It would seem very inconsistent of God to allow the Mayans to discover such an amazing truth while keeping the many Old Testament prophets ignorant of the timing of the events. In summary, there is absolutely no biblical evidence that the 2012 Mayan prophecy / prediction of doomsday is in any sense valid or probable.

Accepting the Mayan 2012 prophecy logically requires acceptance of the following theories: our sun is a god; the sun is powered by the blood of human sacrifice; the creation moment occurred at 3114 B.C. (despite all evidence that it happened much earlier); and the visual alignment of stars has some significance for everyday human life. Like every other false religion, the Mayan religion sought to elevate to the point of worship that which was created in place of the Creator Himself. The Bible tells us about such false worshipers: “They exchanged the truth of God for a lie, and worshiped and served created things rather than the Creator” (Romans 1:25), and “since the creation of the world God’s invisible qualities – His eternal power and divine nature – have been clearly seen, being understood from what has been made, so that men are without excuse” (Romans 1:20). To accept the Mayan 2012 prophecy also denies the clear biblical teaching about the end of the world, because Jesus told us “…of that day and hour no one knows, no, not the angels in Heaven, nor the Son, but the Father” (Mark 13:32).

Many things are 'supposed' to happen. All of them are idiotic hoaxes. Nothing unusual will happen in 2012.

Besides the Mayan Calendar ending?

Nothing unusual. There are numerous crack pot disasters predicted, but they are a bunch of ...

Well, just be careful where you walk. You won't want any of that on your shoes.

Well lets just wait for that to happen,those are just rumors anyway.Just be a blessing to anyone.

An Earth-crossing object named Apophus is predicted, through observations made the past few years and calculations based upon them, to pass closely enough to Earth on, actually I believe it is December 12, of 2012, as to actually be closer than low-Earth-orbital artificial satellites launched from Earth, and possibly close enough to perturb it's orbit enough to alter it's next close pass already predicted through the same calculation methods in 2039 to more possible collision. Currently, (OK as of last year, when I viewed these figures for Apophus and approximately 100 others on the list) the calculated statistical probabilities for collision impact were some significant digit times ten to the minus fourth at worst case and other calculators had it at out to ten to the minus eighth. The same source was very illuminating about the object: It's orbit around the Sun is a sharply elliptical one, as compared with Earth's somewhat circular one, but it's orbital period is, like 0.93 year, and it so remains in a relatively limited slice of Earth's orbital path, crossing back and forth like a picket boat at the mouth of a harbor, and it is only once in awhile that it is in the path at juxtaposition with Earth at that area of Earth's orbit. Let's call this what is 'given' in the world of astrophysics.

On a completely unrelated note the ancient native culture between the Toltecs and the Aztecs in the region of Central America made up of southern Mexico, Honduras and Guatemala today are referred to as the Mayans. Little is left of their culture, not only owing to the fact that the society itself apparently died out as a cohesive social order years before the Aztec culture rose, and decades before the Spanish conquistadors arrived, but thanks also to them and the Jesuit priests that accompanied them most of the writings and indeed glyphs carved in stone and pottery (not to mention those who tried to defend them) were systematically destroyed in order to bring the Good News of the Gospel to the heathens... One thing that has managed to have been discovered about these remarkable people is the fact that they constructed their own Calendar. To occidental minds this conjures an image of the Gregorian Calendar which marks the days in a complete single cycle of the four seasons, concurrently with as it turns out one revolution of the Earth, and more or less evenly divided inot twelve lunar cycles we call months. The Mayan calendar was actually much bigger than that. They had numbers for days and names for groups of numbers of days and not all of the groups had the same numbers. That is where the similarities end. Their calendar spanned a block of time that was much larger, evoked imagery of cyclic occurrences that people today are starting to dicuss not in terms of Global Warming now but Climate Change, and the major divisions ran something like 52 years. Where this begins to get interesting is in the discussion within the texts of the calendar regarding the uncertainty and instability of things in general on Earth during those 52 year cycles, noting that at the end of one, which of course implies the beginning of the next, not only is storm activity up but so is 'the Moon' where normality in the society is concerned, and in fact the Mayan Calendar that we have at this point ends predictably enough at the completion of that cycle, and there is nothing stated or implied as taking place beyond that date and that date when converted back to the Gregorian system winds up Dec 12, 2012. Note that there is nothing that says either the Earth or Time will actually end, they simply stopped the calculation of it. Along with some cryptic allusions that this particular changeover in terms of instability and derangement would be a tough one.

There are some videos taken of this Apophus, rendering it like some crooked Idaho spud tumbling in juggernaut fashion. It appears to me to be made of 'soft debris' like volcanic ash, but where I just do not enjoy the thought of this thing coming for us, not only predictably, but in fact even predictedly, It doen't strike me as that big a stretch to consider that it's offset cylindrical shape could be due to having a great, iron core made like a z-bar. I have tried my best to entertain the astrophysical community with a challenge to assume impact dead in the middle of the Yellowstone Caldera at, say, three times it's current velocity, and then work back through the acceleration towards it's normal orbit, and if at tangency it's within 500 mi I suggest it will simply home in. If you'd like to hear what I would propose we do about it, hit me back, somehow. Ciao.

No such planet around.