The 2012 myth: crossing the galactic plane

A component of the 2012 myth is that on the Northern Hemisphere winter solstice the Sun will cross the galactic plane resulting in an alignment with the galaxy’s central black hole that will result in all sorts of nasty consequences. As discussed with respect to the Mayan calendar myth, there is some science embedded in this, but a little critical thinking exposes the pseudoscience of this part of the myth.

The Sun orbits the center of the galaxy once every 230 million years or so, and oscillates above and below the galactic plane (an imaginary plane that divides the galaxy into “upper” and “lower” halves) about three times during each circuit. Two recent estimates (by R.M. Humphreys and J.A. Larsen in  Astronomical Journal and R.L. Branham in Astrophysics and Space Science) place the Sun’s current location between 20 and 30 parsecs from the plane (a parsec is equal to 3.26 light years), and moving towards its maximum distance of between about 50 and 90 parsecs (J.N. Bahcall and S. Bahcall in Nature). So, no crossing will occur in 2012 or any time in the near future.

But, just for the sake of argument, let’s assume that the Sun was crossing the plane. Because the shape of our solar system’s orbit is roughly circular, it is no closer to the center of the galaxy at that time than any other. The gravitational effect of the central black hole on earth is always there, and always the same. And it is negligible. If it wasn’t, the earth would likely have wandered off into space long ago.

A little more math reveals that our solar system has experienced nearly 60 galactic plane crossings in the last 4.5 billion years (in about 20 orbits). Every one of those ought to have been sufficient to produce whatever dire circumstances are predicted for this one, and the last one would have put a real crimp in the evolution of our species.

Ah, but this is going to occur on a solstice. That makes it special, right? Nope. It is true that right now the Sun appears in the sky near (not coincident with) the galactic center at the December solstice. But axial wobble causes the solstice positions of the Sun against the stars to move across the sky in a 26,000 year cycle. It’s a coincidence, that’s all. Attributing significance to the solstice is crossover from astrology, where precession of the equinoxes (which shift for the same reason as the solstices) forms the basis for the various “new ages” of that field of pseudoscience.

What will they think of next, unknown planets colliding with earth? Solar eruptions? Magnetic field reversals? Sure, why not?

More info about the Milky Way: Wikipedia

Answers to 2012 questions: NASA Ask an Astrobiologist