The Earth rotates on its axis each day, so the sun rises and sets every day. The Earth is in constant orbit around the sun, and it takes a full year to complete one orbit. But the Earth isn’t steady—it wobbles a little as it moves, which is called “precession." Think of a top or gyroscope: the bottom point stays on the surface, while the top point rotates around in a circle. Earth does the same thing, just not very quickly.
It takes 26,000 years for the precession of the equinoxes to make a full circuit. Every year for the last 1000 years, on the winter solstice, the Earth, Sun, and galactic equator come into alignment. So if this happens every year, why is there so much emphasis on the winter solstice of December 21, 2012?
Some people have concerns that the alignment will include a large black hole at the center of the Milky Way galaxy, called the “dark rift” or “Mayan Black Road." This black hole cannot be seen because of the dark clouds surrounding the center of the Milky Way. When this alignment occurs, disasters will fall upon the Earth, such as earthquakes, volcanic eruptions, tsunamis, diseases and famine.
This galactic alignment was predicted to occur in 1998 +/- eighteen years, which puts it between 1980 and 2016. There are arguments that this alignment happened in 1998. However, it could be that it may be different on December 21, 2012 because all planets and all twelve Zodiac constellations will also be in alignment.
Astronomers argue that the galactic equator is an arbitrary line and can’t be marked precisely because we don’t know where the Milky Way begins or ends. Other scientists argue that the black hole is so far away that it cannot be seen, and it can’t affect the Earth. They also believe that the alignment of 1998 was more precise than any alignment that may occur on December 21, 2012, and nothing bad happened to the Earth in 1998.
NASA argues that the sun will be off the galactic center by 6.6 degrees, and that is the closest it will get. And, it will happen a few days before December 21, 2012, so there is nothing for our planet to worry about.