Contrary to the wackos, the conspiracy theorists, and a recent movie, the world will not end on December 21, 2012. First, although the thirteenth Baktun cycle of the Mayan calendar does end then, the Mayans did not associate anything special with that date. Second, the sun will not line up with the galactic center on that date. Third, there is no special alignment of the planets on December 21, 2012. All of these issues are clearly explained by E. C. Krupp, chief astronomer at the Griffith Observatory in Los Angeles. Krupp is a frequent contributor to Sky and Telescope, the premier magazine for amateur astronomers, and the astronomy of ancient civilizations is one of his specialties. Here is a link to his article, "The Great 2012 Scare" from the November 2009 issue.
There is also a good theological reason for saying that the world will not end on December 21, 2012 or at any other time that some unbalanced publicity seeker announces. When the disciples asked Jesus to nail down a date, He replied, "It is not for you to know times or epochs which the Father has fixed by His own authority; but you will receive power when the Holy Spirit has come upon you; and you shall be My witnesses both in Jerusalem, and in all Judea and Samaria, and even to the remotest part of the earth" (Acts 1:8-9). Furthermore, Jesus said, "The Son of man is coming at an hour you do not expect: (Luke 12:40). So when a group of Christians or atheists or cultists expects Him to come, He's not coming then.
When Jesus talked about His Second Coming, He frequently emphasized three things. (1) You cannot know when He is coming. (2) Keep on doing your duty, so that when He comes He will be pleased with you--preach the gospel, care for the poor, love your neighbor. (3) There will be very hard times throughout this age, but suffering is not a sign of the end. Therefore, endure it without giving up your faith in Christ.