Image description
Using the moon solely, one can get a good accuracy of time evolution. Hours can be measured using a "moonlight dial", days can be estimated through moon phases, as well as months thanks to the inclination of the lunar orbit relative to Earth's equatorial plane.
Of course the observation of celestial bodies is still very useful, but considering a solar system as a clock dial would be more complicated than accurate. From one extreme to another, the physical properties of nature also allow for incredibly precise time measurement.
Going from the moon clock to the atomic clock was truly a revolution.
Description of how this image was created
This shot has been ready for a few weeks, but I decided to wait until the very end not to spoil the concept of someone else. This 3rd shot was not really important, but it is kinda cool I think, so there it is. It looks like a hybrid between the first two. We have the timekeeping aspect together with infinitely many clocks that should or not cover the entire background when we take the speed of light and the origin of the universe into account.
Technically, there is nothing really special about it. The moon phases are made of 8 independent renderings gathered into a texture. Obviously, the light used for a moon must not illuminate the other moons. The "atomic" look of the moon clock comes from an anisotropic specular reflection.
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