Bob Thiel, the on-ordained self-appointed prophet, chief revelator, Mayan authority and world renown authority on prophecy says that the tribulation now cannot start until 32 things he has prophesied happen first.
Now, while Armageddon itself is a term used in the Bible for the location where armies in the end time will gather for battle, what the astronomer is trying to say is that comets, if large enough, could end civilized life of earth. Some believe that a comet incident will do something in November and/or December this year, and it very well might. It should be noted that it is well know that solar flares and electromagnetic pulse (EMP) weapons could do that, or at least eliminate computers from many parts of the earth.
Of course, in the future, there are real electrical risks for the USA, Canada, UK, and other nations. But most ignore warning signs.
That being said, the ‘great tribulation’ itself will not start on December 16, 2013. Perhaps I should mention that world events also aligned with at least 32 predictions in my book 2012 and the Rise of the Secret Sect (a list can be found at the beginning of the old article End of Mayan Calendar 2012–Might 2012 Mean Something?). And yes, I do believe my biblically-understood prophetic views about the start of the ‘great tribulation’ will also be correct.