Move the mouse around and watch what happens.

United States Official Time page -
This public service is cooperatively provided by the two time agencies of United
States: a Department of Commerce agency, the National Institute of Standards and
Technology (NIST), and its military counterpart, the U. S. Naval Observatory (USNO).
http://www.time.gov/

Worldtimeserver.Com - Look up the time around the Planet.

The latest information on Network Time Protocol
(NTP) and other related clock synchronization products
http://www.eecis.udel.edu/~ntp/

Sunrise/Sunset Computation

U.S. National Clock - U.S. Naval Observatory (USNO)

Your Computer Time