The H. Moser & Cie. Endeavour Chinese Calendar Limited Edition

There are few subjects more beautiful than the various calendar systems which have developed over the tens of thousands of years that H. Sapiens has been looking up at the sky, but there are also fewer subjects more difficult. The three basic cycles on which calendars are based are the day (the rotation of the Earth on its axis) the month (the time it takes for the Moon to orbit the Earth) and the year (the time it takes for the Earth to revolve around the Sun). The problem is that none of these cycles divide evenly into each other – the year, for instance, isn’t an even number of days. There are 365 days in a calendar year, but the actual year is closer to 365.2422 days and so once every four years, in a Leap Year, we add an extra day to the month of February to keep the calendar from drifting out of alignment with the seasons. This has kept makers of perpetual calendar clocks and watches in business ever since 1582, which is when Pope Gregory put his foot down and established the calendar that has taken his name.

There is however, as the old saying goes, more than one way to skin a cat, and while the Gregorian calendar ignores the lunar month, there are plenty of lunar calendars in use around the world, which take as their basic cycle the time between successive new Moons. This period is known as a “synodic” month, from the Greek “synodikos,” meaning a meeting – in this case, of the Sun and the Moon, as the new Moon occurs when the Moon is between the Earth and the Sun (which is also when eclipses can occur, if things are lined up just right). Makers of moonphase watches love to boast of their accuracy, with deviations from the actual synodic month measured in one day’s error over periods of centuries or even thousands of years. The dirty little secret behind such claims, though, is that the accuracy claims are based on an average synodic month – the actual length of a synodic month can vary by about 29.18 to about 29.93 days.

The upshot to all this is that if you want a lunisolar calendar – the best of both worlds, or maybe the worst, depending on your appetite for complicated orbital mathematics – you have to come up with all sorts of workarounds to keep the months from drifting out of synchronization with the year. The Chinese calendar, which is about 2,500 years old, uses 12 lunar months of either 29 or 30 days, based on an approximation of 29.53 days for the lunar month. That means that a lunar year of 12 months contains 354.36 days and therefore has 10.88 days fewer than a solar year, which lasts 365.25 (again, approximately). In order to keep the lunar months aligned with the calendar year, the Chinese calendar inserts an extra month once every two to three years. The Chinese calendar divides the solar year into 24 “solar terms” which are confusingly also sometimes called “months” and which have names corresponding to seasonal and agricultural events.

The Chinese calendar is no longer the official Chinese calendar but as it is used to set the date of some important holidays, including the lunar New Year, it is still in use and since 1928, it has been under the management of the Purple Mountain Observatory, near Nanjing (which, I’ve read, can no longer be used for observational astronomy due to light pollution).

There have been several watchmakers who have created Chinese calendar watches, including Blancpain (which I believe was the first) and more recently, Parmigiani Fleurier, but the Moser Endeavour Chinese Calendar is undoubtedly the easiest to read if you can’t read Chinese characters (both the PF and Blancpain Chinese Calendar watches use Chinese characters on their dials). Moser, however, has opted for a Chinese calendar watch which presents the essential information of the Chinese calendar in the clearest and most straightforward fashion I’ve seen in any Chinese calendar watch so far.

The basis for the watch is Moser’s perpetual calendar mechanism, and the date of the Gregorian calendar is shown at 6:00, just below the small seconds indication. Two crescents to the right and left show the day of the lunar month and moonphase (on the right) and the lunar month itself (to the left). The small window up top has two indications – the Chinese character tells the sign of the Zodiac for the year, and if there is an extra month, the number of the month is shown as well. The extra month in the Chinese calendar can be inserted anywhere between the 2nd and 11th months and has the same number as the month preceding it, with an extra character added to show that it’s the extra month.

The intercalary month is also called an “embolismic” month, which might sound a little alarming if you are familiar with the use of the term in medicine, where an embolism is an obstruction in an artery. The word however is, like “synodic,” derived from ancient Greek, and simply means, to insert – in this case, a month in a calendar rather than a blood clot in a coronary artery.

Now, it’d be nice if both the Chinese calendar and Gregorian calendar were perpetual but unfortunately, there is no periodic cycle of intercalary months in the Chinese calendar. This is because it’s partly based on the orbital motion of the Moon and as we hinted up above the motion of the Moon in its orbit as seen from Earth is extremely complicated, which means you cannot calculate a gear train for the lunar part of the lunisolar calendar. There is a thread on the astronomy Stack Exchange in which one respondent comments, “The American Mathematical Society’s webpages on sea tides states: ‘The tidal force is governed by … astronomical motions [of the Moon] which are themselves periodic, but since the various frequencies have no whole-number ratios between them, the whole configuration never repeats itself exactly.'” The Moser Endeavour Chinese Calendar, therefore, gets around the problem through the use of two cams which provide the correct indications for a twelve year period, during which none of the calendar indications need to be manually re-set; at the end of twelve years, however, the watch will need to go in for a service and to have the cams switched out.

This is an honorable solution if you ask me and one which has been enshrined in tradition by Patek Philippe, which used a cam (or program wheel) to encode the date of Easter in the Caliber 89 pocket watch (the date of Easter in the Gregorian calendar does follow a periodic cycle but it takes over five million years to repeat). The Endeavour Chinese Calendar is a pleasing and ingenious combination of two distinctly different calendars, both of which represent the attempts by different civilizations to inject some sense of regularity into an inherently irregular system of celestial mechanics, and it does so with one of the most easily legible and harmonious designs I’ve ever seen in a calendar of this complexity.

The H. Moser & Cie. Endeavour Chinese Calendar Limited Edition: Case, red gold, 40mm x 13mm, sapphire crystals front and back, with midnight blue fumé dial and Moser logo in transparent lacquer. Movement, caliber HMC 210, 32mm x 8.1mm, running at 21,600 vph in 33 jewels; Straumann balance spring, with 3 day power reserve. Hours, minutes, small seconds, Chinese year and intercalary/embolismic month, retrograde displays of the Chinese months, and lunar days and moonphases, with Gregorian calendar date at 6:00. Limited edition of 100 pieces worldwide; price at launch, $76,800. Visit Moser to find out more.