I’ve come across a couple of sites which serve to provide real-time updates about which parts of the planet are currently dark, and when exactly sunrise is going to occur.
First, DaylightMap.com shows the pattern of night and day on a Google map, for any area of the Earth, for any date and time. It also allows you to select up to ten locations on the map; in addition to seeing at a glance whether it’s daytime there, you can show their local time, sunrise and sunset times, and length of day.
Secondly is the Sunrise and Sunset tracker. This app doesn’t have quite the same sophistication, and fewer options, but I kind of perfer the simpler interface.