[reaperducer]

I don't know if anyone knows an app that gives first-light and last-light for the phone, so I don't have to buy a new watch?

I'd like one that takes into account terrain. All of the apps I've seen believe the world is a perfectly smooth. I live in a place with mountains, and my "last-light" time at certain points of the year can be as much as 50 minutes earlier than any app will predict.

[bondolo]

It could be written. There is a dataset of world elevations at 1km resolution that I saw being used for calculating the horizon distance from arbitrary points. Searching just now it turns out that was low resolution data, 30-arcseconds and 1 arcsecond, 30m resolution is available! https://www.usgs.gov/faqs/where-can-i-get-global-elevation-d...