Submission of a Proposal for a Commission: Letter of Intent Proposed Commission Name of the Commission: Rotation of the Earth Temporary Commission code: NC-18 Proposer details Name: Richard Stewart Gross Institute: Geodynamics and Space Geodesy Group Jet Propulsion Laboratory Postal Address: Mail Stop 238-600 4800 Oak Grove Drive 91109 Pasadena United States Email: [email protected] Telephone: +1 Commission Category Regular Commission Parent Division: Division A Fundamental Astronomy Co-Proposers First Co-Proposer First Name: Florian Last Name: Seitz Institute: Technical University of Munich City: Munich Country: Germany Email: [email protected] Second Co-Proposer First Name: Jose Last Name: Ferrandiz Institute: University of Alicante City: Alicante Country: Spain Email: [email protected] Third Co-Proposer First Name: Vladimir Last Name: Zharov Institute: Sternberg Astronomical Institute, Moscow State University City: Moscow Country: Russian Federation Email: [email protected] Rationale Commission replaces existing Commission: Division A Commission 19 Rotation of the Earth Text: The proposed Commission on Rotation of the Earth renews the activities of existing Commission 19 (http://www.iau-comm19.org) and is created to support and coordinate scientific investigations on Earth rotation and related reference frames. The Earth rotates about its axis once a day, but does not do so uniformly. Instead, the rate of rotation fluctuates by as much as a millisecond a day, the Earth wobbles as it rotates because the Earth's mass is not balanced about its rotation axis, and the Earth's rotation axis precesses and nutates in space. These variations in the Earth's rotation are caused by processes acting within the interior of the Earth such as coremantle interaction torques and glacial isostatic adjustment, by processes acting at the surface of the Earth such as fluctuations in the transport of mass within the atmosphere and oceans, and by processes acting external to the Earth such as torques due to the gravitational attraction of the Sun, Moon, and planets. Studying the Earth's time varying rotation can therefore be used to gain greater understanding of these and other global-scale processes of the Earth. 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 1922-1967 it became IAU Commission 19 on "Latitude Variation" and since 1967 it has been IAU Commission 19 on "Rotation of the Earth". 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 the rotation about the pole). (2) Serve the astronomical community by linking it to the official organizations providing 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. The Commission meets its objectives by fostering research and discussion on Earth rotation and reference frames by organizing topical symposia and workshops and by forming relevant Working Groups. During the upcoming triennium, it is expected that the Commission will organize at least one Symposium on Earth rotation. The Commission proposes to continue the IAU/IAG Joint Working Group on Theory of Earth Rotation. The purpose of the JWG is to promote the development of theories of Earth rotation that are fully consistent and that agree with observations and provide predictions of the Earth orientation parameters with the accuracy required to meet the needs of the near future as recommended by, e.g., GGOS, the Global Geodetic Observing System of the IAG. The JWG was created at the 2012 IAU General Assembly and should continue for another term. The Commission will work closely with the Services, Commissions, and Global Geodetic Observing System of the IAG as it has in the past. In this manner, the astronomy community is kept abreast of progress being made by the geodetic community in observing and understanding the Earth's rotation, and vice versa. The Commission will be led by a President, Vice President, and Secretary supported by an Organizing Committee (OC). The main Proposer of the Commission will become the President of the Commission. The Vice President of the Commission will be elected by the members of the Commission. The Secretary will be appointed by the OC. The four founding members of the OC are the four proposers of the Commission. An additional four members will be subsequently elected to the OC following the new IAU procedure. It is expected that of the four elected members, one will represent the IAG, one will represent the IERS, and one will represent the IVS, leaving one memberat-large. The representatives of the IAG, IERS, and IVS are expected to also represent the other IAG Services and Commissions that are not otherwise represented in the OC. Any member of the IAU who is interested in participating in the Commission may become a member of the Commission. The existing Commission 19 has 183 members. It is expected that the proposed Commission will have a similar number of members.