Jack Forster at Hodinkee has a wonderful deep-dive essay on the Solar Dial face on Apple Watch, which was added last year in watchOS 6:
Tapping the Solar Dial watch face will allow you to see whether it’s day, or night, or one of the various phases of twilight. You can also see how many hours of daylight there are. The color of the sky also changes depending on the time of day, and during the twilight hours, you get a very pretty transition from blue, to a deeper blue, to a lovely pale pink as the solar disk begins to sink below the horizon. You can rotate the crown to show you what time sunset takes place, as well as the various phases of twilight. You’ll also see, in yellow numbers in the sub-dial, how many hours it is from the current time to sunset, or other solar astronomical events.
I give the Apple Watch Solar Dial a lot of credit for taking the properties of the smartwatch and using them to create a very captivating experience. The luminosity of the display and its ability, as night falls or sunrise dawns, to display different colors, as well as the general composition of the dial, makes for something much richer and far more emotionally evocative than the mere delivery of information. And too, it gives us a chance to reflect on what darkness and light have meant, and continue to mean, culturally and historically. There is something irresistibly compelling about having a little model universe on your wrist.
It’s remarkable how much attention to detail Apple gave to this watch face, including the intricate nuances of the different phases of twilight. I’ve never used the Solar Dial face before, but Forster’s piece has changed that, and I’m eager to see how the face transforms throughout the remainder of today.