It's a well known phenomena that day/night lengths vary throughout the year with latitude. From no variation at the equator to the extreme 24 hour days and nights near the poles. This app helps you visualize this variation. Enter your latitude/longitude or choose your location on a map. You'll get a visualization of the length of days/nights throughout the year at that location. The system will estimate the appropriate timezone for each location and adjust for 'wall clock' time accordingly.
On the chart black is night (obviously), yellow is day and the blue band is twilight. If there is daylight saving in the timezone then you will see a discontinuity in the sun rise/set curve during the transitions.
You can have one or two locations (although a HD monitor will be required to fit both charts side by side).
Some interesting well-known observations:
1. Here in Ireland the days get depressingly short during the winter and we all get a bit cranky, sick, moldy and drink too much. 
2. At the equator, day/night is pretty much same all year around. They all have a happy disposition and they don't drink at all! 
3. Up near the arctic circle there comes a point in the year where the sun doesn't rise at all. Oddly up there there they don't seem to get nearly as cranky, sick or moldy as we do in Ireland, but they still drink too much.
Some lesser known observations:
1. The length of twilight varies with latitude. In fact you can estimate latitude using just that 
2. The shortest day of the year, the day of latest sun rise and the day of earliest sun set are not the same! (ie the sun rise and set curves are not exact mirrors of each other)
This app uses HTML5 has been tested with the latest Chrome and Firefox browsers. It will probably will cause Internet Explorer to explode.
App at this location: http://a-fine-stretch-in-the-evenings.appspot.com/
 I'm in Galway, Ireland at 53.3N, 9W.
 There are exceptions!