2009 sees Friday the 13th occurring in two months in a row after 11yrs

For the first time in 11 years, 2009 registered Friday the 13th falling in two consecutive months-February and March.

And what's more, the double whammy can only occur in certain non-leap years and only in a February-March combination.

In fact, one can look for another of the Friday the 13th combo in 2015. If this wasn't enough, the double threat isn't the only Friday the 13th claim to infamy for 2009, a particularly tough year for superstitious minds.

The ominous date falls on three Fridays this year: February 13; this Friday, March 13; and again on November 13.

However, three Friday the 13ths in one year is the maximum it can get, at least until we follow the Gregorian calendar, which Pope Gregory XIII ordered the Catholic Church to adopt in 1582.

"You can't have any [years] with none and you can't have any with four because of our funny calendar," National Geographic News quoted Underwood Dudley, a professor emeritus of mathematics at DePauw University in Greencastle, as saying.

The calendar works just as its predecessor the Julian calendar did, with a leap year every four years.

But the Gregorian calendar skips leap year on century years except those divisible by 400.

For example, there was no leap year in 1900 but one was observed in 2000. This trick keeps the calendar in tune with the seasons.

Thus, Dudley noted that we have an ordering of days and dates that repeats itself every 400 years.

And in this order, some years such as 2009 appear with three Friday the 13ths. Other years have two or one.

"It's just that curious way our calendar is constructed, with 28 days in February and all those 30s and 31s," said Dudley.

And there's one more revelation with the 400-year order in practice: The 13th falls on Friday more often than any other day of the week.

"It's just a funny coincidence," said Dudley.

Richard Beveridge, a mathematics instructor at Clatsop Community College in Oregon, authored a 2003 paper in the journal Mathematical Connections on the mathematics of Friday the 13th.

He noted the 400-year cycle is further broken down into periods of either 28 or 40 years.

"At the end of every cycle you get a year with three Friday the 13ths the year before the last year in the cycle ... and you also get one on the tenth year of all the cycles," he said.

Two thousand nine is the tenth year of the cycle that started in 2000.