The app calculates the sunrise and sunset times of your location, with these you can plan your activities in advance. You can also get the sunrise and sunset times for any day in the past and future.
Note that due to atmospheric conditions, the actual sunrise and sunset times may be a few minutes away from the calculations.
Hint: If you want to know if there is sunlight, the civil twilight times listed in the app is more useful.
(This app can still work if you deny location access, but in that case latitude and longitude need to be manually inputted.)