Planning ahead doesn't guarantee that you'll get the shot, but it sure does help enormously to maximize your chances. And for anyone shooting outside--and even sometimes inside--knowing where the sun is becomes second nature in the moment, but what if you want to frame a particular shot with the sun or moon in the frame for tonight, next week, or next year? Or what if you want to make sure that a particular side of a building, mountain, or tree is catching direct sun or in shadow?
A great tool developed by Stephen Trainor helps solve this issue. Coming in two flavors, one for the desktop (via Adobe Air) and another for iPhone, the Photographer's Ephemeris (or, in the developer's shorthand, TPE), shows you on a Google map where what direction the sun and moon will be relative to any given point. It includes handy information on moon phases, rising and setting times, and a host of other related information like compensating for atmospheric refraction.
So if you're looking for that perfect shot of the full moon lined up with the Washington Monuments right at dusk, you can find out when that occurs (answer: Harvest Moon in September). Or if you want to know the precise moment when Manhattan Henge occurs when the setting sign is perfectly lined up with Manhattan's grid streets (see also DC Henge), when the best chance of catching the sunbeam in Grand Central Station is, or want to know where to position yourself to catch the sunset and the Eiffel Tower in the same frame, or if you want to get a sunrise at just the right spot over a mountain range, it'll help you find the perfect angle and position to set up for your pre-dawn stakeout. It really is a very handy piece of software. And the iPhone app means you can also find out on the go, although you'll have to be getting bars on your phone since it relies on being able to access Google Maps on the fly for map and elevation data (a version that used locally saved maps would be great). The Photographer's Ephemeris works great along, but using it alongside Magic Hour and Helios Sun Position Calculator gives you a lot of flexibility.
Now, if only it could do something about pesky clouds spoiling the fun. . .