Dec 21st 2012 is a hoax; most probably a valid astronomical discovery by the Mayans turned into a complex scam to generate collective attention by the masses on a series of intellectual concepts aimed at cashing in on the "Mystery".
Human minds are that weak (about anything, btw).
You should be more worried about these upcoming **inevitable** events;
- Nuclear arsenals use for any reasons (Civilian societies paying the heavy price for military or religious freaks)
- next Ice age (cyclic, variable degrees of intensity, potential for huge extinctions)
- Asteroid_S or Comet_S striking Earth (can actually reset the clock on evolution of whomever survives)
- Magnetic tilt, shifting the whole technological devices to waste (+/-, electricity, production stops, agriculture vanishes, chaos -- possibly for decades or less)
- Biological epidemics, mutation of bacteriologic "competition" aiming to eliminate the human species or more (reproduction fails - for example)
- Politics, Economics, Mythics, Prophetics (influence can go a long way towards hiding the truth from the most in order to PROFIT or abuse whatever power any groups have)
None of which can actually destroy our planet or the ENTIRE population.
Right now the odds are waaaaayyyyyyy against us... but we can VERY easily spin these tables to our favor, if only to escape Earth itself if & when necessary since the galaxy is vast enough. I'd say we're about a millenium or two behind a rational target for inter-stellar colonizations too busy that we were staging (and spending energy, money, time, etc) wars against anyone else here.
ETs are watching & laughing; they're even on their way to conquer us polluters.
And, you're worried about some Galactic scale transition or coincidental relative locations of anything? Yep, we move in space -- or remain static & dumb.