World day/night clock applications are nothing new, of course, with examples on everything from the oldest Psion handheld to the current state of the art smartphones. But Day / Night Map brings the idea to Windows Phone in a variant on Mercator projection, showing which bits of the globe are in sunlight at any time on any day.

From the minimalist Windows Phone Store description:

A world map that shows the regions of day light and night.

It updates once every minute.
Date and time of day can be selected.

As with all such map projections, take the relative sizes of the countries and land masses with a pinch of salt - it turns out that the Earth really is round - but having it laid out in 2D does help work out which places can currently see the sun. Attempts to map this onto a 3D-rendered globe usually fall foul of 'not being able to see well near the edges'.

Here's the somewhat clumsily-named 'Day / Night Map' in action:

Sunrise, sunset, for your current location, plus the current sunlight map for the current time, though (right) you can adjust this to show the map for any date or any time if needed...

Tapping the full-screen tool brings up this landscape view showing more detail. Nicely done, though there's no option to override the usual screen lock, so you can't leave this going as an animated screen saver or demo.

In fact, in addition to the visibility (sic) of where it's day and where it's night, there's also here the rather useful facility to explore sunrise and sunset times for any day of the year. Yes, there are calculators for this sort of thing elsewhere, but Day / Night Map is a useful utility to bring these functions together on your phone.

There's a 30 day free trial in the Store here.