I was doing some calculations using exact sunset and sunrise times which I got from SkySafari Pro Android, by looking at the exact time the center of the sun passed the horizon (altitude 0). However, the times differed by some minutes from what I was expecting. I checked on my PC using Stellarium, and that gave me values more close to prediction. For example, for my location (51d27m0sN, 5d28m40sE), I find times using SkySafari of 7:25:57 and 19:34:27 for yesterday (22-9), while Stellarium gives me 7:29:42 and 19:30:51 for the same location. Given that it was the autumnal equinox yesterday, I expect a duration between sunrise and sunset close to 12 hours, but with the times from SkySafari, I find a duration of approximately 9 minutes more, which seems too much.
Does anybody know an explanation for these results, or if I might be doing something wrong?