“For GPS to work, the orbital position, or ephemeris, of the satellites has to be known very precisely,” said Chopo Ma of NASA’s Goddard Space Flight Center in Greenbelt, Md. “In order to know where the satellites are, you have to know the orientation of the Earth very precisely.”

To get a stable reference point for global positioning, GPS systems have to turn to something that is stable. The earth is moving, the sun is moving, the stars are moving so what’s stable? Well quasars are so remote they do not seem to be moving relative to earth and our solar system. [...]

Source: Space.com – click here for full article