The New Year is upon us, a time when we often think about, well, time: times past and what the future might hold. And while you can never go back, sometimes years do repeat themselves, or at least the calendar does. The New Year of 2013 will have the same calendar as 1991, 1985, 1980, 1974, 1963, 1957 and so on going back through the years. How do you find out what years have matching calendars? Now you can go online to sites such as that created by the Archives at Notre Dame University. They have a page devoted to perpetual calendars where you can find a year just by typing in a day and date, reverse the search and find the day based on the year, or find years whose calendars match.
But why would anyone need to know this stuff, aside from the interesting trivia factor? Archivists and historians refer to perpetual calendars when trying to find a complete and correct date for documents and photographs that only contain partial information. For instance, if a letter has a date of Tuesday, January 29th and you know it was written in the 1970s, looking at a perpetual calendar shows you that there was only one year in the '70s that had that configuration: 1974.
Another calendar tie-in archivists may make is if their collection actually contains old calendars. Such is the case with the UCLA Archives where the Library Special Collections Blog has an entry about their collection of medical and scientific calendars. They even have a link where you may download your own copy of calendars from 1889, 1895 and 1907, which are also the same as 2013.
Whatever calendar you use, all of us here wish you a very Happy New Year!