When is Easter this year? As it's linked to astronomy, you need a special timepiece to find out. Like Stonehenge. Or (more practical), a perpetual calendar watch.
In fact, people have been timing yearly events for thousands of years, using massive stone observatories, right through to handier items by Patek Philippe, Jaeger-LeCoultre and the other great Swiss watch marques.
Was Stonehenge a perpetual calendar? Built in about 2700 B.C., its stones include alignments with sunrise, sunset, moonrise and moonset, while some scientists think that it was used as a sort of perpetual calendar. The oldest feature of the monument consists of a ring of 56 holes, with markers that were moved around these holes from day to day. For example, moving the Sun marker anticlockwise by one hole every 13 days, the Moon marker anticlockwise two holes a day, and two other markers moved at different rates, would enable the user to predict the phases of the moon, and solar eclipses, corresponding to when all the markers were aligned.
Later in history, timepieces were made that could keep track of the date of Easter, the first Sunday after the full moon following the March equinox. This function is a feature of only the most complex grand complications, such as the famous Patek Philippe Calibre 89, built in 1989 for the company's 150th anniversary. Only four were made: the pocket watch has 24 hands and 1,728 components, which power features including perpetual calendar, moon phase, date of Easter, time of sunrise, star chart and many more. It is smaller than Stonehenge, but fairly hefty all the same, 9 cm in diameter and weighing 1.1 kg.
A more accessible perpetual calendar is offered by the Patek Philippe 5940, which has an ultra-thin self-winding movement, and a perpetual calendar that records day, date, month, leap year and phases of the moon. The gold rotor can be seen through the transparent caseback. In an attractive cushion-shaped case, the Calibre 240 Q automatically adjusts for the different lengths of the months, and leap years, so that if kept wound, it will remain correct until the year 2100, when the Gregorian calendar requires a correction consisting of considering what would normally be a leap year as a normal year.
There is no doubt that the perpetual calendar is one of the most useful complications for a watch, and many brands have launched new models in 2013. Click here to read more.