I use the Darkness app whenever I have an outdoor shoot. It's a great reference to know exactly what time the sun rises and sets. You've heard of the "golden hour"—that hour after sunrise and before sunset? I usually schedule portrait shoots during the golden hour, so I like being able to look up the exact time for perfect lighting while I'm on the phone with a client. When I was in Paris, I used the app every day to make sure I was at the right spot at the right time. Yes, I know there is also a "golden hour" app that costs twice as much and includes "a database of over 50,000 carefully selected locations from every country in the world," but for me, that's overkill. I prefer to find my own locations, and unfortunately, I only regularly visit a couple of countries.
I know I sound like an ad, but I really do use this app all the time. I have my faves— Orem (that's Utah, folks), New York, London, and Paris—all lined up on one page. With my bad attitude about the short winter days (sunset at 5 p.m. is just plain wrong!), I can at least be grateful that I get exactly 1 hour and 7 minutes longer before sundown here than I would in London. I'm sure the Londoners are just dying with envy.