It is well known that futurology, the science of forecasting the future, is a very difficult science. It also depends on the intervals of time for which we pretend to forecast the evolution of the physical system under consideration. Aldous Huxley thought that futurology might be a very good thing.

With the advent of more precise methods for measuring Earth rotation, a number of corrections to the apparent directions in space, to the terrestrial references, and to the rotation axis motion have to be carefully applied. It is the duty of the international Astronomical Union to give recommended or conventional expressions of these corrections in order to avoid inextricable difficulties in discussing the evaluated results. However, this task is not sufficient. The concepts used in the description of the Earth's rotation are somewhat obscured by traditions. They should be purified by removing notions which are not directly relevant.

In 1976 a new state primary time and frequency standard of the USSR was certified and confirmed with an error of reproducibility less than 1 × 10−13 and with an unavoidable systematic error less than 3–4 × 10−13. This standard includes a laboratory primary cesium beam frequency standard providing an independent definition of units in the SI system, primary hydrogen frequency standards preserving the units of frequency and time intervals, and hydrogen and cesium clocks providing the TA(SU) and UTC(SU) time scales.

Processing of astronomical observational data of several time services and the publication of Universal Time of emission of time signals has been carried out in the USSR continuously for fifty years. Currently the Universal Time computations are made in the USSR State Time and Frequency Service using the observational data of eleven Soviet time services and ten time services of socialist countries that have volunteered to participate. The functioning of this system simultaneously with the BIH system that unites time services from all over the world has certain practical advantages. The Soviet Universal Time scale UT1 (SU) may be influenced by some geophysical effects which are characteristic of the Eurasian continent, and consequently, it may be used advantageously for scientific and practical purposes in this region. The agreement between different time scales, produced by various methods and observational data, also makes it possible to evaluate the reliability of these scales.

The reference systems for the determination of UT1 and polar coordinates are discussed. Some arguments are given in support of the adoption of the mean pole origin (MPO) defined by the mean latitudes of the observatories. Taking into account the frequency response of the filters used by the BIH and the U.S.S.R. Time Service, the effects of the errors of the adopted nutational coefficients and tidal variations of the vertical are estimated.

Chollet has analysed a homogeneous series of astrolabe observations made at Paris since 1956.5 in order to derive corrections to the principal terms of nutation. Comparison of his results with others obtained recently indicates that the values and would be suitable for adoption.

For the study of the Earth's rotation and geodetic measurements the longest possible series of homogeneous Universal Time (UT) data is required. For various reasons this remains a difficult problem. Periodically it is necessary to revise past observations and redetermine the UT scale. This was done by the Bureau International de l'Heure (BIH) in 1968 when the FK 4 catalog, revised values of astronomical longitudes, and new techniques were standardized for the reduction of astronomical observations. This system known as the 1968 BIH System has been in use since 1968 and has also been used for the re-reduction of observations back to 1962.0.

The nature of the irregular fluctuations in the speed of the Earth's rotation was investigated using ninety-day means of UT2 - A.1 determined at the U. S. Naval Observatory. Data from June 1955 to April 1978 were included in this study. Statistical analysis of the excess length of day shows no evidence for the persistence of discrete values for periods on the order of five years. No statistical basis for the existence of discrete “turning points” in the rotational speed could be found.

Spectral analysis of the acceleration data shows that the rotational acceleration of the Earth during this period of time may be represented by a constant term plus random changes in acceleration occurring with a frequency greater than once per year. The magnitude of these changes appear to be consistent with estimates of meteorologically induced changes in the rotational acceleration.

An autoregressive integrated moving average (ARIMA) model was fit to the excess length of day data. This model permits simulated series of excess length of day data to be constructed. These simulated series show a statistical similarity to observations made since 1820. However the apparently large changes in the acceleration which occurred around 1870 and 1900 are twice that which can be reasonably accounted for by this model. The details of this analysis will be published later.

Observations of the Earth's rotation have shown irregular variations of rate which have characteristic times of decades. These have been attributed to transfer of angular momentum between core and mantle by some mechanism such as inertial coupling, viscous stress, electromagnetic coupling or stresses produced by topographic features on the core mantle boundary.

The maximum entropy power spectrum (Smylie, et al., 1974) of the Earth's rotational speed was calculated using data from 1900 to 1976. Two series of data were analyzed. The first was a series of δω/ω) determined from annual UT1 - ET data from 1900 to 1976. The second was a similar series derived from the mean monthly data of UT1 - TAI. Linear trends were removed from both series before analysis. Using the second series of data, significant periods of 2.8, 3.7, 7.0, and 10.5 years were found. The first series showed significant periods at 6, 10, 13, 22, and 57 years. Of these periodicities those at 22 and 57 years showed the largest amplitudes (0.454 ± 0.097 × 10−8 and 1.431 ± 0.104 × 10−8 respectively).

The variations of the atmospheric angular momentum were investigated (Sidorenkov, 1976). Using the climatic cross-sections of the zonal wind, the values of the relative angular momentum of the atmosphere, h, were calculated for each month. The variations of h during the year are shown in Figure 1, where curve 1 illustrates the sum of h for the entire atmosphere, and curves 2 and 3 illustrate h for the atmospheres of the northern and southern hemispheres respectively.

The theory and instrumentation of a photographic zenith tube (PZT) have been described by various authors (Torao, 1959; Markowitz, 1960; Thomas, 1964; Schuler, 1968; Takagi, 1974). Analysis of the more recent results of the PZT's of the U. S. Naval Observatory at Washington, D. C. and Richmond, Florida, permit the determination of precision and accuracy estimates which may be expected from the daily operation of a PZT. This analysis shows precisions of in latitude and in time, determined from the internal error of one sight. Accuracies estimated from the external error of a sight were found to be in latitude and in time.

Twenty years of time and latitude observations made with the Herstmonceux Photographic Zenith Tube have been analysed to determine the phase and amplitude of deflexions of the local vertical at the frequency of the semi-diurnal M2 tide. The results have been compared with predictions incorporating new calculations of the gravitational attraction due to the M2 tides in the surrounding seas. The effects of the zonal Mm and Mf tides on the time observations have also been determined and compared with existing theory. In both cases the agreement is reasonably good.

PZT observations of the Earth's rotation and polar motion have been carried out from observatories near Ottawa and Calgary since 1952 and 1968 respectively. A comprehensive re-evaluation and analysis of the PZT data is currently under way, using a new self-contained computer program which can easily accommodate changes of astronomical constants as well as modifications of the star catalogue.

Use of new techniques (Doppler, laser, VLBI) has yielded such results that many astronomers believe that in the near future these techniques will replace classical instruments for observations of the Earth's rotation. None of the modern techniques has furnished observational series which demonstrate that systematic errors in the polar coordinates and UT1 are stable over sufficiently long intervals. Investigations of known phenomena such as sudden changes of the secular term in UT1 - UTC (Munk and MacDonald, 1960), changes of the amplitude and phase of the seasonal irregularities (Fliegel and Hawkins, 1967; Pavlov and Staritzin, 1962), secular motion of the mean pole (Mihailov, 1971; Markowitz, 1960), continental drift (Stoyko, 1938; Djurovic, 1976), quasi-diurnal nutation of Molodenskij (Popov, 1963; Toomre, 1974; Rochester et al., 1974), etc., are complicated by the existence of systematic error variations (accuracy), and to a smaller degree, on the accidental errors (precision). The BIH and IPMS make use of individual series of astronomical latitude. ϕi, and (UTO - UTC)i from up to 82 classical instruments (Guinot, 1976). If the systematic errors in these series are independent, the polar coordinates and UT1 - UTC determined from a combination of observational series would result in an improvement of accuracy by at least one order of magnitude through the mutual compensation of the variation in systematic errors. At present, however, it is uncertain whether mutual independence of modern observations (a basic condition for mutual compensation of errors) will be better than that of the classical instruments.

Periodic terms with arguments such as (α−2L) and (2α−2L) etc. which appear via various phenomena in the results of time and latitude observations by PZT are summarized in analytical forms in order to clarify their mutual relation. Numerical values in time and latitude for these terms to be expected at the Tokyo PZT are also given. From the data of time observations obtained by the Tokyo PZT during the past 15 years, amplitudes of the terms, cos(α−2Lα) and sin(2α−2Lα) in time, are obtained as +0.72 and 1.21 ms, respectively. These results give the value of (l+k-ℓ) as 1.14, and the values of nutation coefficients for 2L, and