Intro

The Galactic Alignment is the alignment of the December solstice sun with the Galactic equator. This alignment occurs as a result of the precession of the equinoxes.
Precession is caused by the earth wobbling very slowly on its axis and shifts the position of the equinoxes and solstices one degree every 71.5 years. Because the sun is one-half of a degree wide, it will take the December solstice sun 36 years to precess through the Galactic equator (see diagram below).
The precise alignment of the solstice point (the precise center-point of the body of the sun as viewed from earth) with the Galactic equator was calculated to occur in 1998 (Jean Meeus, Mathematical Astronomy Morsels, 1997).
Thus, the Galactic Alignment "zone" is 1998 +/- 18 years = 1980 - 2016. This is "era-2012."
This Galactic Alignment occurs only once every 26,000 years, and was what the ancient Maya were pointing to with the 2012 end-date of their Long Count calendar.

These are the astronomical facts of the matter. From a larger perspective, we can visualize the 2012 Galactic Alignment in the following way:

Position A is where the December solstice sun was in relation to the Milky Way some 3,000 years ago. Position B is 1,500 years ago. And position C is "era-2012", when the December solstice sun has converged, as a result of the precession of the equinoxes, with the exact center-line of the Milky Way (the Galactic equator). Notice that the place of alignment is where the 'nuclear bulge' of the Galactic Center is located.
A long awaiting digital portrayal of precession and galactic alignments is now available on Nick Fiorenza's web site.