It only happens twelve times per century, to be exact. I am referring to the date and time stamp on this post. It happened on morning of January 1 of 2001, then again on February 2 of 2002. Then, every 13 months and one day since then. The last time will be early afternoon on December 12, 2012. Have you figured it out? Look carefully at the date and time stamp. September 9, 2009 at nine minutes, nine seconds past nine o'clock in the morning.
Okay, perhaps is not as obvious to some: 09/09/09 09:09:09, or the moment when the month, day, year, hour, minute and seconds are identical. I say in the morning, because on the 24 hour clock, 9:09 PM is 21:09. 12:12 AM is 00:12.