In case you haven't heard, there's a piece of hysteria going around (pumped up by movie marketing) that the world will end on December 21, 2012, supposedly based on astronomy and an ancient Mayan prediction.

Did the Mayans really think this? Is the astronomy for real? Do we actually have anything to worry about? The answers, not surprisingly, are "no," "no," and "of course not."

To make a long story short, December 21, 2012, really is a big flip-the-page date in the ancient Mayans' calendar. But there's no evidence that they believed the world would end then, and a fair amount of evidence to the contrary. Not that it would matter if they did. As for the planetary and galactic lineups that latter-day doom-mongers have tried to associate with that date, they're flat-out wrong.

But you probably have friends and family who are getting nervous that America will crack apart into cookie crumbs, tsunamis will sweep over the Himalayas, Earth's poles will flip, and a secret invisible planet will smack us down like a bowling pin. And they will be turning to you, the astronomy person, to ask about it.

We have the stuff you need to tell them. Noted archaeoastronomer E. C. Krupp explains all the details, and the history of this mania, in the cover story of the November 2009 issue of Sky & Telescope, now available at a newsstand near you. You probably won't find it in your supermarket, but it should be on the magazine rack in any good bookstore. And if it's sold out, you can always subscribe!

Incidentally, in that same issue, S&T editor-in-chief Robert Naeye describes some cosmic catastrophes that actually could happen — and explains why they're not likely to strike in the next millennium or two. Humanity has more pressing things to worry about.

P.S. A tidbit from Krupp's article: Boston University has a Center for Millennial Studies, and its director, historian Richard Landes, points out that throughout history, failed end-of-the-world movements have numbered in the "hundreds of thousands at least." There's never a shortage of people eager for everything to go kaput. Or at least to spin hoaxes about it.