Agent Moulder had it right.
Astronomers know when the planets will be in alignment. And, as he indicated, this is generally an illusion of sorts, because the planets are virtually never on the same line of sight to us, because their orbits have diferent planes.
A big time planetary alignment generally refers to an event that occurs about once a century, and describes where the visible planets are all within about 10 degrees of each other in the sky....not exactly aligned, but within about a fist-width of each other when viewed at arm's length. It's pretty cool, but utterly menaingless.
Most planetary alignments involve two...perhaps three planets, but whatever the case, there is no physical effect or real meaning to such an event in the heavens. It's like solar or lunar eclipses. They are merely interesting visual phenomena. They have some scientific observation value, expecially in the cases of totality in solar eclipses, but they have absolutely no effect on anything.
The 2012 business is nonsense. Planet X, or Nibiru, doesn't exist. There is no planetary alignment that can possibly have any effect on the planet Earth, and passage through the galactic equator (which has been ongoing for a decade) is also physically meaningless.
Nothing's going to happen as a result of any of these things, imagined, or real!
You really want to get excited about celestial happenings, 2010 is the year for that! We have Mars in opposition on 27 January, which will make the red planet pretty darn prominent in the winter skies; the Moon will be full on 29 January, and sitting right next to Mars...and, it'll be the largest full Moon of the year, as the Moon will be closest to Earth on that date.
Saturn will be at opposition on 21 March, with it's rings almost flat to us....it will be the last time you'll get to see that until about 2025.
In April, you'll be able to easily observe both Venus and Mercury in the dusk skies. Mars and Regulus (a red planet and a blue star) will nearly meet in early June skies; the Perseid meteor shower will peak on 11 August...highlighted by a rare Moonless night for observing it; Jupiter will be it's biggest and brightest in 40 years on 21 September, and above it, you can spot blue Uranus at oppostion as well. At 23:00 ET that night, if you have the right optics, you'll also see Europa transit Jupiter's surface that night.
You've got Venus at it's brightest in December, the Gemenid meteors, and , on 21 December:
The century's first total lunar eclipse which will be visible form the U.S. through Canada...with the Moon as high in the sky as it will be until 2020.
It's a remarkable year for astronomical observing opportunities. Really cool stuff...but you shan't see Nibiru anywhere!
...however, I do expect comments on the numerology associated with these 2010 events...
Jupiter, Uranus, and Saturn all at opposition on the 21st. The highest full Moon of the decade, and a total lunar eclipse, on the Winter solstice, 21 December ! !
I can't imagine these events won't spark some threads!
The person with a telescope has a field day in store with real astronomy in 2010. That's alot more compelling than Nibiru, or fantasy's generated by paranoid pseudo-scientific web pages about doom surrounding events that either don't exist or which cannot possibly have any effect on anything...