November 26, 2009 05:55 AM EST
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The Milky Way Galaxy is a barred spiral galaxy and has about four arms that go out and one of those arms we call the Sagittarius arm. That Sagittarius arm is where the Solar system is at. The Sun's orbit around the Galaxy is expected to be roughly elliptical with the addition of perturbations due to the galactic spiral arms and non-uniform mass distributions. In addition, the Sun oscillates up and down relative to the galactic plane approximately 2.7 times per orbit. This is very similar to how a simple harmonic oscillator works with no drag force (damping) term. These oscillations often coincide with mass extinction periods on Earth; presumably the higher density of stars close to the galactic plane leads to more impact events.
It is important to define what the Galactic Alignment is in precise astronomical terms. 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.
