I’m curious how the time and date are derived. Is this done as an API from a service, or pulled internally from the watch?
Specifically I’m looking to create a face that include some astronomical information such as Civil, Nautical, and Astronomical Start and End times. While you can do some math to approximate this, to be specific you need to know the angle of the sun below the horizon. This is different at different longitudes and times during the year. So approximations would vary wildly depending on the user and their location.
If the API is not an option, can you provide an expression for the latitude and longitude. It is not in the current list of expressions or tag, but based on my research should be provided to the OpenWeather API to derive the watch location.
If we had those two items, I’m sure between me and @Mellin we could figure out how to calculate things using the guide here (Sun rise, set and twilight times calculated using a simple iterative scheme and implemented as a QBASIC program, an Excel spreadsheet using VBA and as a plain spreadsheet.) …maybe.
Sunrise and sunset are often defined as the instant when the upper limb of the Sun’s disk is just touching the observer’s mathematical horizon assuming a spherical earth, and allowing for the atmospheric refraction. This corresponds to an altitude of -0.833 degrees for the Sun. The various ‘twilights’ are usually defined in terms of the Sun’s altitude as follows;
_ Astronomical twilight altitude -18 degrees_
_ Nautical twilight altitude -12 degrees_
_ Civil twilight altitude -6 degrees_