Commission A2 Rotation of the Earth

Scientific Objectives

Knowledge of the Earth’s time-varying rotation is also needed to connect the terrestrial and celestial reference frames to each other. The terrestrial reference frame is attached to the solid Earth and its orientation with respect to the celestial frame changes as the Earth rotates. Knowing the relative orientation of the terrestrial and celestial reference frames and how it varies in time allows the positions of objects such as interplanetary spacecraft tracking stations to be known in both frames.

Commission 19 has a long and proud history of active involvement in the IAU. During 1919-1922 it was known as “Standing Committee” 19 on Latitude Variation with Hisashi Kimura as its President. During 1922-1964 it became IAU Commission 19 on “Latitude Variation” and since 1964 it has been IAU Commission 19 on “Rotation of the Earth”. It adopted its current name in 2015 as a Commission under Division A.

The objectives of the Commission are to:

1. Encourage and develop cooperation and collaboration in observation and theoretical studies of Earth orientation variations (the motions of the pole in the terrestrial and celestial reference systems and rotation about the pole).
2. Serve the astronomical community by linking it to the official organizations that provide the International Terrestrial and Celestial Reference Systems/Frames (ITRS/ITRF and ICRS/ICRF) and Earth orientation parameters (EOP): International Association of Geodesy (IAG), International Earth Rotation and Reference Systems Service (IERS), International VLBI Service for Geodesy and Astrometry (IVS), International GNSS Service (IGS), International Laser Ranging Service (ILRS), International DORIS Service (IDS).
3. Develop methods for improving the accuracy and understanding of Earth orientation variations and related reference systems/frames.
4. Ensure agreement and continuity of the reference frames used for studying Earth orientation variations with other astronomical reference frames and their densification.
5. Provide means of comparing observational and analysis methods and results to ensure accuracy of data and models and encourage the development of new observation techniques.

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