Terrestrial coordinates

image courtesy from: http://en.wikipedia.org/wiki/File:The_Earth_seen_from_Apollo_17.jpg	The starting point for measuring east-west locations on Earth is the prime meridian at the Royal Observatory in Greenwich, England. The reference for south-north locations is the equator.
The terrestrial coordinate system works great on earth, whereas for interplanetary space travel and to identify the precise position of stars beyond the solar system other coordinate systems are more suitable. Click on the Earth in the picture above