Okay, so I’ve been messing around with this Timex watch, the “Sun and Moon” one. I wanted to figure out how the sun and moon indicator actually works. Here’s how it went down.

Getting Started
First, I got the watch, obviously. I made sure I had good lighting, because, you know, tiny parts and all that. I also grabbed my basic watch toolkit – nothing fancy, just some screwdrivers, tweezers, and a case back opener.
Opening it Up
The first thing I did was pop off the back of the watch. This Timex has a snap-on case back, so I used a thin blade to carefully pry it open. I’ve learned from past mistakes to be super gentle here, so I wouldn’t scratch anything up.
Inspecting the Movement
Once I get the back off, I am able to see a plastic movement holder to keep the quartz movement secure. I carefully removed this using my tweezers, setting it aside. I was then able to take the movment out from the case.
The Sun and Moon part
I was able to get a closer look and quickly identify the sun and moon disk.See the disk with the sun and moon painted on it? It’s geared directly to the hour wheel, that’s the part that makes the hour hand go around.
- It wasn’t a separate module or anything complicated.
- It’s a simple disk with the sun and moon pictures.
- It rotates with the hour wheel, but at a different rate.
Figuring Out the Rotation
Here’s the key part: the hour wheel goes around once every 12 hours, right? But the sun and moon disk needs to go around once every 24 hours (to show day and night). So, the gearing has to make that happen. The gearing slows down the rotation of the sun/moon disk so it takes a full 24 hours to complete one revolution.

Putting It Back Together
After I figured out how it worked, I carefully put everything back together. I placed the movment back in place. Then reattached that plastic movement holder, making sure it’s secure.
Then I aligned the stem with the movement, put the back on, and snapped it shut. Making sure to press evenly around the edges to get a good seal.
Final Thoughts
It’s actually a pretty simple mechanism, once you see it up close. It’s all about the gearing between the hour wheel and the sun/moon disk. Pretty neat how they get that 24-hour cycle out of a 12-hour movement. Just a bit of clever engineering, really.