Jack Forster has published a fascinating piece for the watch experts at Hodinkee that takes a deep dive look at the Solar face in watchOS 6 for Apple Watch Series 4 and Series 5:
The Solar Dial consists of a 24-hour dial with 12 (noon) at the top and 24 (midnight) at the bottom. An hour hand moves once around the dial per day, and attached to the hour hand is miniature representation of the Sun. The portion of the dial that’s in light blue represents the number of daylight hours, and the portion in dark blue, night; the boundaries between each section mark sunrise and sunset. Opposite the Sun on the 24-hour hand is a smaller dial which shows the hours and minutes, in either an analog or digital format.
The piece is loaded with intricate details about how the admittedly complex watch face works, including a lesson on the many phases of twilight between day and night:
In order, therefore, the sequence starting at Sunset is: Sunset, Civil Twilight, Civil Dusk; Nautical Twilight, Nautical Dusk; Astronomical Twilight; Astronomical Dusk … and finally, Night proper. This is followed by Solar Midnight, which is the moment when the Sun is at its nadir on the celestial sphere from the standpoint of the observer. […]
Twilight has its own rich vocabulary, including the word crepuscular; “that which is related to twilight.” Animals that are chiefly active during the twilight of dawn or nightfall are called crepuscular animals; my favorite of these, and maybe yours too, is the firefly.
Forster then shows each phase from sunset to night that the Apple Watch Solar face presents. Each section is like a user guide for what Apple’s Solar face means.
Read the full piece on Hodinkee.