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Frequently Asked Questions About Earth Orientation

What is Earth Orientation?
- Refer to the IERS Conventions for detailed information on definitions and models.
How do we observe Earth Orientation?
What causes variations in the Earth's orientation?
Who uses Earth Orientation information?
What is Polar Motion?
What is Earth Rotation?
What is Length of Day?
What are Celestial Pole Offsets?
What is a leap second?
- Information about leap second announcements.
Refer to the Naval Observatory Vector Astrometry Subroutines, NOVAS, package for software to compute a variety of astrometric quantities and transformations.
Who contributes data to the Earth Orientation Parameters combined solutions?