There are also concerns that planets or stars might line up in ways that will transform Earth. For instance, some theorists claim that from our point of view, the sun will cross in front of the plane of our galaxy on Dec. 21. However, the sun already does this twice a year, Yeomans said.
In fact, the sun will eventually cross the plane of our galaxy. However, the sun is about 67 light-years from the galactic plane, so it should take several million years to do so, Yeomans said. Even then, when our solar system finally does cross the plane, nothing special will occur, he added. [10 Failed Doomsday Predictions]
Some also claim that gravitational effects from planets lining up with each other will somehow affect Earth. However, there is no planetary alignment due on Dec. 21, 2012, "and if there were, it wouldn't cause any problems," Yeomans said.
The only bodies that have any significant gravitational impact on Earth are the moon and the sun, effects we see as the tides. Tidal effects from other bodies in our solar system are negligible at best, and in any case, we have experienced them for millions of years without notice.