Investigation of Joy’s Law According to the Data of the Ussuriisk Astrophysical Observatory

Based on the 66-year series of observations of the Ussuriisk Astrophysical Observatory, the angles of inclination of the bipolar axes of sunspot groups (tilt angles) have been studied. It is found that the average tilt angle is 6.8° ± 0.2°, and the angles of inclination of sunspot groups in the northern hemisphere of the Sun, on average, are 1.0° larger than for the southern one. It was also found that the average tilt angles are practically independent of the maximum area of the sunspot group. The dependence of the tilt angles averaged in 5-degree latitudinal zones Tm from the heliographic latitude F in the first approximation is described by a linear function Tm = 0.16° + 0.43∣F∣. However the dependence Tm(F) also demonstrates significant deviations from the linear function, which look like two almost horizontal sections (“plateaus”). One of them is located near F = 15° and the second is at F > 25°. Dependencies Tm(F) calculated for groups of sunspots with small, medium, and large areas do not reveal significant systematic differences. These results are compared with the previously published results of the study of five series of data on the tilt angles of sunspot groups.