Who uses Earth orientation information?
Anyone who must relate changing aspects of reference systems on Earth to a system in space requires information on the Earth's orientation. Users include navigators, geodesists, and those involved in timekeeping. For navigators using celestial navigation, failure to account for the changing UT1, in particular, could result in significant positional errors.
Other users are those concerned with navigation in space. Precise positions of satellites located hundreds to tens of thousands of kilometers away in space must take into account the Earth's variable rotation. Without this information, the positions of the satellites cannot be accurately related to points on the Earth's surface, which is necessary for many space-based applications. Increasing use of artificial satellites for world-wide navigation and communication makes this area an important concern.