PHILADELPHIA — And it shall come to pass that when the 13th baktun comes to an end, so will the world. Everything, even the entombed red-cinnabar-coated kings, shall be destroyed in an apocalypse. So it has been foretold — and so many believe — by the ancient Maya calendar; even Maya deities like the jade-haired maize god and the goggle-eyed storm god must submit. In Arabic numerals the final date would be represented this way: 13.0.0.0.0.

Talk about bad luck. According to the Penn Museum here, which has mounted a major exhibition that manages to be at once tantalizing, illuminating and frustrating, that day is close at hand. Though many experts calculate it to be Dec. 21, 2012, the museum curators believe it is Dec. 23, 2012. And this show, “Maya 2012: Lords of Time,” opens with a teasing potpourri of tabloid headlines, movie disasters and television news reports invoking the imminent catastrophe (though the exhibition is expected to remain open after the world ends, until mid-January 2013).

It’s a setup, of course, because we soon learn that the Maya civilization (which once extended over modern-day southern Mexico, Guatemala, Honduras, Belize and El Salvador; built major cities by 500 B.C.; and reached its peak before A.D. 900) had no such idea.

In fact, the Maya Long Count Calendar, the focus of the show’s first part, has no end (and no real beginning). Maya kings erected monuments to themselves using that eternal calendar, combining an immense sense of centrality with an immense sense of immensity.