What is Earth Orientation?
The term "Earth orientation" refers to the direction in space of axes which have been defined on the Earth. It is usually measured using five quantities: two angles which identify the direction of the Earth's rotation axis within the Earth (
polar motion), an angle describing the rotational motion of the Earth (
UT1-UTC), and two angles which characterize the direction of the Earth's rotation axis in space (
celestial pole). With these coordinates, the orientation of the Earth in space is fully described. The
Rapid Service/Prediction Center of the
International Earth Rotation and Reference Systems Service (IERS) monitors the Earth's orientation and disseminates this information to many organizations on a continuous basis.