Would you clarify what your point is? The galactic plane is not part of the solar system - I suspect that wasn't what you meant. It's essentially a largely imaginary line drawn along the middle of the galaxy (which is about 1000 light-years thick, moving and not all precisely mapped; there's a lot of wiggle room about where the middle is). Our solar system does pass through the galactic plane every few dozen million years, but we're dozens of light-years away from it at the moment. We're not going to be anywhere near it by 2012 unless someone moves the solar system (or the rest of the galaxy) with a faster than light drive. So it's something else to not be worried about.
In all seriousness, it makes much more sense to worry about alien invasion than about any of the half a dozen ways in which civilisation as we know it is prophecied to be ending on 21/12/2012 (or any time soon).
Lol i meant the galaxy, The Milky Way is a vast spiral galaxy, shaped a bit like a spinning record; just one that measures 100,000 light-years across and only 1,000 light-years thick. Imagine you were below the Milky Way, and passed through the disk of stars above it. That moment when you're halfway through the 1,000 light-year thickness of stars? That's the galactic plane.
Astronomers actually use a coordinate system to measure positions in the Milky Way, starting with the Sun as the center point. No, we're not actually at the center of the Milky Way, we're actually off to the side, but this makes the measurement easier. They draw a line from the Sun to the center of the Milky Way, and that defines the 0-degree point, and then coordinates are measured within the galactic plane. You can have galactic latitude and longitude.
Have you heard anyone mention that the Sun is supposed to be crossing the galactic plane in 2012? Yeah, that's a myth. Here's the thing. The Sun does bob up and down in the galactic plane. Sometimes we're above the plane, and then other times we're below the plane. But that cycle takes 64 million years to complete! It's impossible to define the exact moment of when the Solar System will pass exactly through the galactic plane.
And astronomers don't think that anything special will happen when the Solar System does pass through the galactic plane. In fact, it's the times when the Earth is above or below the galactic plane when we might be at risk. A recent scientific study correlated those times with large extinction events in the Earth's history. It's possible that the Milky Way's magnetic field protects the Earth from intergalactic radiation and cosmic rays, and when we're significantly above or below the galactic plane, life on Earth suffers more damage from space radiation.
But that's just a theory.
So, to summarize, the Solar System won't be passing through the galactic plane in 2012. There's no easy way to know exactly when that'll happen, and there's absolutely no way to give that a specific date. And even when we do pass through the galactic plane, there's no risk to our planet.
Here's a link to an article on Universe Today about possible extinction events when the Earth is above or below the galactic plane.
There are just so many ways the Universe is out to get us. Astronomers have already considered the threat from our Sun's orbit around the center of the Milky Way. When our Sun rises up out of flat plane of the Milky Way, it appears we might be less protected from intergalactic radiation and cosmic rays. Well, it looks like passing through the middle of the galactic plane might have its own share of risks: an increased number of comets might be hurled towards the Earth because of gravitational interaction with the densest parts of our galaxy.
Researchers at the Cardiff Centre of Astrobiology have built a computer model of the Solar System's journey around the Milky Way. Instead of making a perfectly flat orbit around the galaxy's centre, it actually bounces up and down. At times it can rise right up out of the galactic plane – getting 100 light years above – and then dip down below it. They calculated that we pass through the plane every 35 to 40 million years.
And this time period seems to match dangerous periods of impacts on Earth. According to the number and age of craters on Earth, we seem to suffer increased impacts every 36 million years. Uh oh, that's a match.
In fact, one of these high points of comet activity would have been 65 million years – the same time that an asteroid strike wiped out the dinosaurs.
And here's the bad news. According to their calculations, the Solar System will be passing through the galactic plane in the near future, and should see an increased risk of impact. Our risk of impact could increase 10-fold.
There might be a silver lining to the bounce, though. The impacts might have helped life spread across the galaxy.
While the "bounce" effect may have been bad news for dinosaurs, it may also have helped life to spread. The scientists suggest the impact may have thrown debris containing micro-organisms out into space and across the universe.
Centre director Professor Chandra Wickramasinghe said: "This is a seminal paper which places the comet-life interaction on a firm basis, and shows a mechanism by which life can be dispersed on a galactic scale."