Today is this year's third and final Friday the 13th, a day and date regarded by some as unlucky. Most years - 42 to 44 years per century - have just one or two Fridays that fall on the 13th. Only 14 or 15 years per century have three. The last of those was 1998; the next is 2012. Guy Ottewell's "Astronomical Calendar" notes that the 13th occurs on Friday more often than on any other day. Just our luck.