A combined length-of-day series spanning 1832-1997: LUNAR97

Universal time (UT) measurements taken by the techniques of lunar occultation, optical astrometry, lunar laser ranging, and very long baseline interferometry have been combined using a Kalman filter to produce a smoothed length-of-day (LOD) series, LUNAR97, spanning 1832.5-1997.5 at yearly intervals. Decadal LOD variations having amplitudes as large as a few milliseconds (ms) are clearly evident in this newly determined series as they have been in previously determined series. Comparing the LUNAR97 LOD series with other available series shows differences that are generally less than the uncertainty in the determination of the LUNAR97 LOD values, which is about 0.6 ms during the early 19th century, improving by more than an order of magnitude to about 0.03 ms during the late 20th century. Decadal LOD variations are, therefore, a robust feature of the lunar occultation, optical astrometric, and space-geodetic measurements of the Earth's rotation that have been taken since 1832.