Astrometric and space-geodetic observations of polar wander

Optical astrometric measurements of star positions taken during the past century have been recently re-reduced using the final Hipparcos star catalog in order to determine variations in the mean location of the Earth's rotation pole with respect to the Earth's crust. This newly available polar motion series, which is the longest homogeneous polar motion series currently available, allows the drift in the pole path to be newly estimated. During the 1900.0 to 1992.0 span of the smoothed Hipparcos polar motion series, the Earth's rotation pole is observed to drift at a mean linear rate of 3.51 +/- 0.01 milliarcseconds/year (mas/yr) towards 79.2 +/- 0.2 degrees W longitude. This new estimate for the observed trend in the pole path, which can be considered to be the present-day expression of true polar wander, is nearly the same as that estimated in previous studies using the homogeneous ILS polar motion series.