Astronomical Latitude Normal to equipotential defined by local gravity vector Direction to North pole defined by position of rotation axis. however rotation axis moves with t to crust of earth Motion monitored by International Earth RotationseRviceIerShttp://www.iers.org/ Astronomical latitude pa=z66人9a δ To Celestial body02/18/03 12.540 Lec 04 5 Astronomical Latitude http://www.iers.org/ • Normal to equipotential defined by local gravity vector • Direction to North pole defined by position of rotation axis. However rotation axis moves with respect to crust of Earth! • Motion monitored by International Earth Rotation Service IERS 02/18/03 12.540 Lec 04 6 Astronomical Latitude d fa zd To Celestial body Rotation Axis fa = Zd-d declination Zenith distance= 90-elevation Geiod 3