“It isn’t necessary to imagine the world ending in fire or ice — there are two other possibilities: one is paperwork, and the other is nostalgia.” –Frank Zappa
There are many websites around telling you that the world is going to end on the winter solstice — December 21st — in the year 2012. And one of the ways that people are saying the world is going to end is that, on this date, the Earth will pass through the plane of the Milky Way galaxy, destroying us all.
Where to begin with this? First off, let me show you what our galaxy looks like. When you look up at an extremely dark night sky, the Milky Way is visible with your naked eye, and looks like this.
It’s huge and expansive, but it’s also quite thick. But we can’t really see what the entire structure of the galaxy looks like because we’re inside of it. Some people are content to rely on an artist’s interpretation, like this.
For me, though, it’s much more convincing to take a look at our galaxy with infrared eyes. Why is infrared special? Because all of that galactic dust and gas that obscures the plane of the galaxy is invisible in the infrared. Thanks to the COBE satellite (and its DIRBE instrument), we can see just what our galaxy looks like.
And we can ask ourselves if this looks like anything that’s out there in the Universe. Of course there is: we look just like every other edge-on spiral galaxy out there!
Spiral galaxies are somewhere around 100,000 light-years in diameter, our Milky Way included. But they’re comparatively very thin: only a couple of thousand light-years thick. And while its true that the Sun, the Earth, and the rest of our Solar System orbits the center of our galaxy, we also move up-and-down through the galactic plane. (That’s plane, not plain, my friendly image generators.)
But this wobbling up-and-down doesn’t happen overnight, or even over the span of many decades. To make one complete trip out of and back into the galactic plane takes about 30 million years. In fact, at the rate we’re moving right now, we won’t cross into the center of the galactic plane for another few hundred thousand years, much less by December of 2012.
But what fearsome things are out there at the center of the galactic plane? What goes on there that we need to be afraid of?
Well, I suppose there’s a higher density of stars there. Slightly. The simple fact is — for all practical purposes — the center of the galactic plane is absolutely no different than our present location in the galaxy. No more stars, gas, dust, radiation, black holes, neutron stars, supernovae, gamma-ray-bursts or anything else that you can conceive of happens in the center of the galactic plane than 10 or 50 or 100 or even 500 light-years away from it.
In other words, the center of the galactic plane is about as special as the Earth’s equator.
Sure, it’s the center. It’s an interesting imaginary line for many reasons, including the definition of latitude. (The Earth’s equator defines terrestrial latitude, while the center of the galactic plane defines galactic latitude.)
But if you actually go to the Earth’s equator, standing on it is no more exciting or interesting than standing north or south of it by a fair bit.
Even if you’re at the famous equator monument in Ecuador.
So while there might be a whole bunch of things to worry about in this world, passing through the center of the galactic plane isn’t one of them, and it isn’t going to happen for another few hundred thousand years!
(But by that point, we’ll all be enslaved by aliens, no thanks to me.)