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.
That said for nearly $700USD I'd rather go for a smart watch. Even though I understand why you wouldn't want one for privacy, distraction/addiction, or whatnot.
https://www8.garmin.com/manuals/webhelp/fenix66s6xpro/EN-US/...
Or check the Solaris watch face which shows civil twilight, nautical twilight, astronomical twilight, and night.
https://apps.garmin.com/en-US/apps/0e019a96-aeb3-4aaf-81ed-4...
Above subject to which device you have.
Check out Sol and Sundial:
https://apps.apple.com/nl/app/sol-sun-clock/id491537291?l=en
https://apps.apple.com/nl/app/sundial-solar-lunar-times/id97...
But errr... isn't the Weather Underground a domestic terrorism and bombing group?
It was acquired by The Weather Channel (later The Weather Company) which was later acquired by IBM.
(Since the bombing group was underground we can of course never know for sure exactly which members were part of the pivot)
https://play.google.com/store/apps/details?id=ch.hbenecke.su...
Why is that?
In the military knowing first-light and last-light, down to within a few minutes, is essential daily. I have an app on my phone that tells me sunrise and sunset, but as the article describes these aren't the same thing. I also have a very expensive top-of-the-range Garmin watch and even that just tells me the less useful sunrise and sunset, which makes me suspicious it's not as military as it markets itself as.
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?