Moonphase watches

For me, the Moonphase complication has to be one of the most attractive and interesting ‘complications’ that a watch can have. I guess my initial interest in it started years ago, when I discovered that I was always the most creatively active exactly during those few days just before the Full Moon. 

First off fun fact: did you know that the moon in reality actually rotates on its axis? Most people scoff when you tell them this, because they always see the same side of the moon when they look up at the sky….That’s because the Moon was created from a chunk of the (proto)-Earth, and somehow within the laws of astrophysics (not my main background) this affects the Moon’s axial rotation – making it turn in perfect synchronicity with the Earth - so we never visually sense its axial rotation.

Back on topic: almost every brand has a nice story about the high, exacting accuracy of their Moonphase watches. Some, like Andreas Strehler’s moonphase watch “Sauternelle à Lune Perpétuelle 2M” is exceptionally, amazingly precise and very cool, with Moonphase gearing that would keep the Moonphase accurate for a gazillion years or so. (Well, actually 2,060,757 years so it seems….Tip top engineering, but of course, only useful if the watch itself can tick that long, and accurately). Andreas Strehler’s greatest achievement in my view is that he has invented a Moon-age indicator that can show the exact age of the Moon down to the hours – a totally novel approach).

However: let’s get down to the hard reality behind all this cool stuff:

1. ANY old Moonphase watch, whether from Patek Philippe, AP, Timex or Fossil, will only need to be reset after about 122.5 years; it just has to do with the principle of a gear with 135 teeth on it…Meaning, you won’t need to adjust the Moonphase during that time…IF the watch never ran fast or slow or stopped and was never serviced during 122.5 years that is 😝.

2. Indeed, since you will need to have your watch serviced once and a while, it makes no difference whether your Moonphase is accurate for 122 years or 1,000,000 years – as you will need to reset it when you get it back on your wrist.

3. Considering a couple of seconds a day gain/loss of the movement, any Moonphase will never stay accurate for even a fraction of a century, however accuractly and wonderfully perfect its gearing has been calculated and executed.

4. There is really no such thing as a mechanically accurate Moonphase indicator, because the Moon rises and falls at totally different times every day, and no Moonphase watch can show you this. In most cases, the Moonphase shown changes just after midnight on your watch, and will normally only be visible many hours later. In a sense a Moonphase indicator on a watch is more like a “phase reminder”, and nothing else, as the Moon rises and falls at such radically different periods daily.

Basically, the quest for highly accurate Moonphase complications by various brands is an example of pure horology – like climbing a mountain because it’s there. It’s at the heart of wristwatch passion: always taking a mechanical challenge and striving to improve every detail possible – even if an iPhone Moonphase App is 1,000 times easier and more advanced!