Caltech/JPL Association for Gravitational-Wave Research Seminar

The rotation and orbit of the Earth cause most of the change in apparent positions of stars. These motions also affect the reduction of measurements of signals from spacecraft and from stars, planets, and galaxies outside the solar system. The accuracy of estimates of the orbits of Earth and planets has improved several orders of magnitude over the past few decades, driven primarily by increasingly stringent requirements for spacecraft missions to Mars. Improved accuracy has come from advances in measurement techniques, availability of signals from spacecraft at other planets, and in models for the motion of the planets in space and time. The current models and measurements used to determine the planetary ephemerides and the resulting accuracies will be discussed.