Q: Does the Mayan calendar end in December 2012?
A: Just as the calendar you have on your kitchen wall does not cease to exist after December 31, the Mayan calendar does not cease to exist on December 21, 2012. This date is the end of the Mayan long-count period but then -- just as your calendar begins again on January 1 -- another long-count period begins for the Mayan calendar.
Q: Is NASA predicting a "total blackout" of Earth on Dec. 23 to Dec. 25?
A: Absolutely not. Neither NASA nor any other scientific organization is predicting such a blackout. The false reports on this issue claim that some sort of "alignment of the Universe" will cause a blackout. There is no such alignment (see next question). Some versions of this rumor cite an emergency preparedness message from NASA Administrator Charles Bolden. This is simply a message encouraging people to be prepared for emergencies, recorded as part of a wider government preparedness campaign. It never mentions a blackout.