SOLAR ACTIVITY IN 1954

Abstract

During 1954, observations of the sun were obtained at Mount Wilson on 337 days, on 213 of which the sun was spotless. The mean number of days per year on which solar observations have been made at Mount Wilson in the last 34 years is 323. Of the 28 completely cloudy days in 1954, 25 were in the winter season, 12 in March alone. There were two long series of spotless days, January 12 to February 7 (27 days), and June 2 to July 2 (31 days). The total number of sunspot groups observed at Mount Wilson in 1954 was 46, compared with 93 in 1953, 219 in 1952, and 294 in 1951. The northern hemisphere was the more active, having 27 groups while the southern had 19. Two of the 35 groups for which magnetic polarities were determined were irregular. The average latitude of the new cycle groups was 27? 7 in the northern hemisphere and 26?5 in the southern. The old cycle groups had a mean latitude of 7? 1 in the northern hemisphere and 4?3 in the southern, compared with 9?9 and 8?6 respectively in 1953, and 10?7 and 10?4 in 1952. Solar activity at the beginning of the year was predominantly in low latitudes, but by the end of the year was mostly in high latitudes. From January through August, 12 groups of the old cycle and 9 of the new cycle were observed. During the remaining four months, however, 3 groups of the old cycle and 22 of the new cycle were observed. A minimum in the smoothed Zurich provisional sunspot numbers occurred in April 1954. Therefore the length of the last cycle was 10.1 years (1944.2-1954.3), the fourth consecutive cycle shorter than 10.5 years. The minimum of 1954 was the lowest since 1913 (see Table I). The sunspot-curve prior to minimum was similar to that prior to the minimum of 1944. Figure 1 shows the distribution in latitude of the groups during the current minimum.