If people tell you to beware the ides of March today, you might want to set them straight--technically, they're seven days too late.

The word 'ides' actually signifies the day of the full moon. And this month, our lunar satellite showed her entire face on March 8, not March 15.

So why the confusion? It all goes back to a change in calendars.

When people refer to the ides of March, they are typically referring to a historical event that occurred in Rome on March 15, 44 B.C.: the death of Julius Caesar. The dictator was assassinated by conspirators who wanted to liberate the republic; they stabbed him 23 times before he bled out, surrounded by his killers.

William Shakespeare immortalized the moment with the tragic play Julius Caesar. In that poetic version of events, a clairvoyant warned Caesar to beware the ides of March.

The phrase stuck. To this day, you'll hear it every year on March 15.

But citizens of Rome measured the passage of time differently than we do today. For one thing, their calendar was not consistent--it was subject to frequent changes, and even Caesar himself executed an overhaul before he died. But in general, months were measured by the moon, meaning that lunar waxing and waning could be accurately predicted by the date.

During March, May, July and October, the full moon always fell on the 15th.

When Caesar died, March 15 really was the ides.  But since that day, we've turned the page on the unreliable Roman calendar. Today's Gregorian calendar is based on earth's orbit around the sun rather than the moon's orbit around the earth, and this keeps us consistent with the changing seasons.

The moon, meanwhile, has fallen out of sync. The ides can happen on any old date, and in March of 2012 it happened on the 8th.

If you want to experience a real ides of March on the same date that Julius Caesar bit the dust 2056 years ago, you'll have to wait a while. The next March 15 full moon is in 2052.