a leaflet map using the Leaflet plugin called Terminator (yes, coolest name ever). the plugin allows overlay of day and night regions on earth. this particular example map shows current areas of day and night with auto-updates every 0.5 seconds for a near real-time geospatial view. you can zoom in and actually watch the night time area move across the earth. view at http://johnwhaney.com/day-and-night.
credit to Jorg Dietrich for developing a really cool Leaflet plugin (with a really cool name). view his documentation for Leaflet Terminator @ joergdietrich.github.io/Leaflet.Terminator/