MacOS Catalina added support for automatic light and dark mode switching.

Sample settings screen

The support article linked above reads:

Auto (available in macOS Catalina): Automatically use the light appearance during the day, and the dark appearance at night.

This doesn't seem to quite capture my experience though, so I'm wondering what the exact algorithm is here.

For example, where I'm currently situated today:

  • in the capital of the country, the sun sets at 18:43 according to Google
  • in my city, it sets at 18:46 according to Google
  • my theme switched from light to dark at 18:57

Is this due to simply different services used by Google and Apple for determining the sunset, or is there more to the switching algorithm than meets the eye?

  • Pure guess, based on historical information. There may be a pre-programmed 'lag' between sunrise/sunset & the switch. I used to use an iQue 360 [early 2000's satnav] which had a user-settable pre-or post switch setting, in minutes. Whatever you set for sunset, you'd get the opposite at sunrise, e.g. lagged sunset, early sunrise change.
    – Tetsujin
    Oct 16, 2020 at 17:15
  • Another theory - they're not that bothered about [or can't guarantee] accuracy. In summer it could take another hour or so to actually get dark, in winter, 10 mins.
    – Tetsujin
    Oct 16, 2020 at 17:24
  • A third idea [sorry] the true time of sunset & the time you actually see the sun drop over the horizon are not the same. The atmosphere bends light sufficiently that you can still see the sun after it's technically gone below the horizon.
    – Tetsujin
    Oct 16, 2020 at 17:27


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