If you simply must know where it is day and night around the world, here are a couple of websites for you.
time.gov keeps the official U.S. time via atomic clock and has a feature which shows where the sun is shining and where it is dark when you click on a time zone. Check it out here
The second website, by John Walker (founder of AutoDesk), offers the Earth and Moon Viewer, which has the day and night feature, as well as views of the earth from the moon, and the day and night sides using satellite imagery. It is much more of a webmapping interface, with query boxes to change the view and type of imagery.
Check out the Earth and Moon Viewer here