A loose-knit Christian movement is preparing for Judgment Day a lot sooner than you might think, after an 89-year-old retired engineer in California predicted that Jesus Christ would return to Earth this Saturday.

But for many others, the prediction has become a punch line that's too hard to resist.

The prophesy originates with Harold Camping, who founded a ministry called Family Radio Worldwide. In broadcast sermons he has been saying that May 21 would bring the Rapture, at 6 p.m. to be precise.

According to Family Radio's website, Camping discovered a mathematical formula from the text of the Bible that allowed him to pinpoint Judgment Day.

The last time Camping made such a prediction was in 1994, although things didn't quite go as he had expected.

However, Family Radio's website maintains that "the accurate timeline of history was revealed to true believers" only a few years ago.

"On May 21, 2011 two events will occur," the group predicts. "A great earthquake (that) will be so powerful it will throw open all graves. The remains of all the believers who have ever lived will be instantly transformed into glorified spiritual bodies to be forever with God.

"On the other hand the bodies of all unsaved people will be thrown out upon the ground to be shamed. The inhabitants who survive this terrible earthquake will exist in a world of horror and chaos beyond description."

Family Radio has mounted an extensive campaign to share its discovery in North America and overseas. Billboards have sprung up from Colorado to Dubai proclaiming that May 21 will bring the end of the world.

The ministry has also organized missions to Iraq and Turkey, where volunteers are asked to use their final days on Earth handing out leaflets. RV caravans are also spreading the word across North America -- including one that will end its journey in Vancouver on Saturday.

But the sensation has also provided fertile ground for jokes from those who don't buy the fringe group's belief.

Jon Stewart took aim at the radio preacher Wednesday night on "The Daily Show," saying that "actuarially speaking he's probably not that far off," given Camping's advanced age.

On Facebook, there's now a "Post rapture looting" page that invites people "to pick up some sweet stereo equipment and maybe some new furniture for the mansion we're going to squat in" once "everyone is gone and God's not looking."

The comic strip "Doonesbury" has also poked fun at the prophesy, and countless "Rapture parties" have been scheduled to celebrate what organizers believe will be the continuation of life as we know it.

With files from The Associated Press