[en] Regiomontanus made 29 measurements of the meridian zenith distance of the Sun in Nurnberg between 1472 and 1475, and Walther made 746 more in the same city between 1475 and 1504. In using the observations, they are first corrected for refraction and parallax. The observed values are then fitted to values calculated from the ephemeris of the Sun. After the fitting the standard deviation of the residuals is 95 arcsec for the observations made by Regiomontanus and 55 arcsec for those made by Walther. The residuals for all groups show strong correlation over considerable periods of time, and they may not be treated as statistically independent. The total variation in zenith distance between the summer and winter solstices was too small by the order of 80 arcsec. The error estimate takes at least partial account of the correlation of the residuals. The corresponding value of the Earth's spin acceleration is -51 +- 91 parts in 10⁹ per century. Thus the observations do not give us a useful estimate of the acceleration. However, they do give us useful information about the actual accuracy of pre-telescopic observations and the performance of early instruments. (author)

[en] The paper deals with the review of works on solar observations at Abastumani Astrophysical Observatory during the past 12 years. The works accomplished on the basis of patrol observations, with the horizontal solar telescope, small and large coronagraphs, and those based on the data obtained during eclipse observations are discussed separately. (orig.)

[en] Initial results of round-the-clock observations of solar oscillations at the South Pole are briefly summarized. (orig./WL)

[en] Global oscillation of the Sun with a period of 160 min were first discovered in 1974 and since observed in Crimea during the last 6 years; they were confirmed, in 1976-1979, by Doppler measurements at Stanford (Scherrer et al., 1980) and quite recently by observations of Fossat and Grec at the south geographic pole. The average amplitude of the oscillation is about 0.5 m s^-1. The phase shows remarkable stability at the period 160.010 min and good agreement between different sites on the Earth; therefore, this oscillation should now be recognized as definitely of solar origin. It is probably accompanied by synchronous fluctuations in the IR brightness and radio-emission of the Sun, and exhibits a dependence of the amplitude on the phase of solar rotation (with a peak of power at 27.2 days). In agreement with results of the Birmingham group and the South Pole observation we also find evidence in favour of a discrete spectrum within the 5 min global oscillations of the Sun, with the average splitting of about 69,5 μHz in frequency. Strict gas-dynamical equations being solved in the adiabatic approximation for a polytropic sphere n = 3 display the pattern of radial oscillations with wave separated by 120 m time-intervals filled with high frequency (and split by 117 μHz) oscillations implying a similarity with the observed pattern. (orig.)

[en] A procedure is described that should allow photographic recording of the complex amplitude of photospheric oscillations as a function of the position on the solar disk. Underlying acoustic sources might be visualized by observing such an hologram under coherent illumination

No abstract available

[en] The physical meaning of the convection efficiency parameter of Oepik's theory is clarified by relating it to that of the mixing-length theory. A compact comparison of both theories is presented to explain the earlier findings of Gough and Weiss (1976), that Oepik's theory becomes indistinguishable from the mixing-length theory when the value of Oepik's cell depth is taken as being equal to 2.44 times the local pressure scale height for the solar convective envelope. (Auth.)

[en] Using Potsdam vector magnetograms and a force-free model, we have investigated the magnetic field structure of the active region BBR 18474 of 1982 July 15, and 1982 July 16. By comparison of the azimuths of the current-free model of the magnetic field structure in the central part of this active region with the map of the azimuth values estimated from the observation we find a good qualitative agreement. Additional earlier results have show, that the appearence of highly sheared magnetic field structure near the neutral line in the central part of this active region may be a simulated effect generated by a subphotospheric current system. (author). 6 refs

[en] Solar surface rotation has been measured from sunspot drawings made in A.D. 1642-1644 and probable differences from present-day rates are found. The 17th century sunspots rotated faster near the equator by 3 or 4%, and the differential rotation between 0 and +-20⁰ latitude was enhanced by about a factor 3. These differences are consistent features in both spots and groups of spots and in both northern and southern hemispheres. It is presumed that this apparent change in surface rotation was related to the ensuing dearth of solar activity (the Maunder Minimum) which persisted until about 1715. (Auth.)

[en] We perform an analysis of the number of sunspot groups in activity cycles from 1610 through the present. Here we use the G_n index, which is defined as the average daily number of sunspot groups in cycle n. There is a high positive correlation between the parameter G_n in the current cycle and an analogous parameter in the following cycle G_n+1 both for pairs of even-odd cycles and odd-even activity cycles. In cycle Nos. 10-21 for pairs of even-odd cycles, the ratio of parameter G_n corresponds to the GO rule G_n+1^odd/G_n^even>1. However, during the period ∼1745-1850, odd cycles were less than the preceding even cycles G_n+1^odd/G_n^even<1. The ratio of the parameter G_n+1^odd/G_n^even has a long-term variation within the range 0.5-1.5 with a period of about 21 activity cycles, and it proves the reversal of the GO rule