There are about one and a half billion ethnic Chinese on this planet. I didn’t take a census or anything, I just Googled it. Out of these one and a half billion Chinese people, I’d say that less than a few hundred of them really understand how the Chinese calendar works. Once again, this is based on my entirely unscientific observations, but I have no doubt that they hold true. Ask the next Chinese person you see. There’s one and a half billion of us; you won’t have to wait long.

The Chinese calendar is one of those complex systems — a lunisolar calendar — that attempt to reconcile the solar year (365.24 days to the nearest two decimals) to the lunar month (29.53 days to the nearest two decimals). Obviously this doesn’t really work out, which is why Chinese calendar dates are always leaping about with respect to the more familiar Gregorian system. Every few years we’re obliged to add an extra lunar month — the leap month — in order to keep pace with the solar year, which the Gregorian calendar is analogous to. Sounds simple enough doesn’t it?

The problem, of course, is that you’re not allowed to just stick an extra lunar month in wherever and whenever you feel like it. The leap lunar month is only implemented when 13 new moons occur between one winter solstice and the next, and it is inserted immediately following the lunar month in which the sun does not cross a line of celestial longitude that is an integer multiple of 30. (It took me hours to internalise and condense the Wikipedia entry on the Chinese calendar so that I could write that one sentence, by the way. I know no one really cares, I’m just saying.)

What you’re probably thinking by now is, why go to all this trouble to knit together two clearly uncooperative systems? You’d have an easier time organising the Israeli–Palestinian peace process. Mathematically speaking, the lunisolar calendar is an absolute nightmare to actually try and achieve. In the first place, using the day as a base unit is problematic, since its actual length varies significantly over the course of a year. Also, as you can see above, neither the solar year nor the lunar month are complete multiples of a day, so what is this I don’t even.

What kind of masochist astronomer does this to himself? If you are in fact wondering this, you’ll be surprised to learn that there are lots of variations of lunisolar calendar floating around. The Jewish calendar, for example. The Hindu calendar too. Lots of ancient calendars are lunisolar, actually, which just goes to show that in the past people had a lot more time on their hands. I guess that’s good for us, because otherwise I wouldn’t be writing this article, and you wouldn’t be getting to hear about the next big milestone coming up in the history of watchmaking. (Chill out, I’m getting to it.)

Ever heard of the Metonic cycle? Please say no, otherwise I’ll feel like I’ve just wasted everyone’s time here. If you’re thinking that it is yet another way of trying to make the solar year and the lunar month get along like ebony and ivory (sitting together in perfect harmony on your incredibly anti-conservationist piano keyboard), you’re totally right. It turns out that — despite what you may have heard elsewhere — 19 is the magic number. Some Greek dude called Meton who lived in the 5th century BC figured out that 19 solar years (ie, 6,940 days) is just about equal to 235 lunar months. I say “just about”, because there is in fact a small difference of a few hours. Honestly though, are you really going to let a few measly hours get in the way of celebrating the fact that this guy worked it all out over two and a half thousand years ago, when half the people you meet today can’t even work out the dinner tip without consulting five iPhones and a juggling monkey?

Let’s get down to functionality, because you know we crazy about actually learning to use the information on our watches. The 19-year Metonic cycle can sometimes be used to predict eclipses. Because of how closely it approximates the 18.03-year eclipse cycle, otherwise known as a saros, it’s possible to have up to five eclipses happening exactly 19 years apart. There’s all sorts of neat calculations to show how you actually pinpoint the exact dates, and the type of eclipse, but we won’t go into that here. (I got part of this information off an HTML webpage that features bright red Times New Roman text on a black background, something which I didn’t think was allowed in the 21st century, and I can’t look at it for more than five minutes, I swear.)

The Metonic cycle also figures in the computation of Easter, which falls on the Sunday following the first ecclesiastical full moon after the spring equinox. The first full-moon date after the spring equinox repeats itself every 19 years, but the days of the week don’t make any effort to accommodate any other system of time, which is why the date of Easter Sunday hops around as it does. So here we are trying to fit everything nicely together, adding leap seconds, days and months here and there, and the days of the week just could not be bothered to show even the tiniest bit of flexibility. They’re the bad guys here, if you think about it. Bunch of Pharisees.

Because the Chinese calendar is lunisolar, it also aligns itself neatly along Metonic rules. I usually have two birthdays a year, because I track my date of birth along both the Gregorian and Chinese calendars. Or rather, my mother does, and she tells me when it’s my Chinese calendar birthday. (I don’t need any reminding about the other one.) Both days line up perfectly every 19 years, which is pretty cool, if you like the idea of celebrating two of your own birthdays at once.

Here’s a fun fact, and I realise I’m really stretching the definition of “fun” in this instance: although it’s called the Metonic cycle, it wasn’t really invented by Meton. I mean, he worked it out properly and integrated it with one of the best-known Hellenic calendars, which is why it’s named after him. It’s generally accepted, however, that the Babylonians were using the 19-year cycle long before Meton was born. Way to bogart all the credit, Meton.

Now that you know absolutely everything you could ever have wanted to know about the Metonic cycle, here’s when I tell you that Vacheron Constantin are creating a watch that displays the Metonic cycle, among other equally amazing things, and that you can’t have it.

Don’t feel bad about it or anything. We can all join hands in our bittersweet admiration of a work of art that will never touch our unworthy carcasses. It’s a super-complicated, double-dial watch that was begun eight years ago as a challenge issued by one of the world’s foremost collectors of mechanical watches. From what I can tell, it’s going to feature extremely classic aesthetics and a totally knockout movement. The Vacheron Constantin official statement promises that we will see “resolutely 21st-century thinking” in this watch, which I fully expect. The thing about Vacheron Constantin that no one ever believes, simply because everyone’s fixated on how classically beautiful their watches are, is that there are some incredibly progressive minds and attitudes driving their product philosophy.

The Metonic cycle indication on the Vacheron Constantin "Grand Oeuvre"

The Metonic cycle indication on the Vacheron Constantin “Grand Oeuvre”

The watch, which they’re coyly calling the “Grand Oeuvre” for now, comes with a perpetual calendar, with indication of leap year, indication of the weeks of the year, seasonal indications, zodiac indications, sky chart, times of sunrise and sunset, length of day and night, carillon repeater with Westminster chime, alarm, indication of sidereal time, and finally the power of automatically making you the most interesting person in the room (to people like me).

The indications of the solstices and equinoxes, zodiac and seasons

The indications of the solstices and equinoxes, zodiac and seasons

It’s also got a multi-axis tourbillon with a spherical hairspring, which looks totes amazing, I don’t care what anyone else says. Not sure why people are dismissing it on the grounds of having seen something similar from another brand previously. You don’t have to play it cool and front around this one incredible watch just because you saw another incredible watch a couple years back. That’s like saying you wouldn’t have dinner with Miranda Kerr because you already had dinner with Adriana Lima last week. I mean, seriously, who thinks this way?

I’ve left lots of things out, obviously. The watch, which some industry insiders know by its code name “Project Tivoli”, doesn’t launch for like another three weeks. Vacheron Constantin have told us to look out for entirely new complications, which I assume they’re totally holding back in order to leave us all gaping in slack-jawed awe during the final reveal as they move in mysterious ways their wonders to perform.

Stay tuned for our review and coverage of the watch when it finally does break. It’s gonna be epic.