Abstract
The present sunspot cycle, No. 19, has proved to be exceptional in several respects. One of these is in the number of highlatitude groups which have all or at least some members at or above ± 40° latitude and have lasted more than one day. Normally a few high-latitude groups appear during a cycle, mostly near sunspot minimum. The greatest number of such groups to occur in any cycle was eight, in cycle 18.1 In the present cycle (through July) there have been eighteen. Seven occurred in 1956 and seven in 1957, with the maximum of this cycle occurring apparently in the vicinity of 1957.0. The two highest groups had members above 50° (October 1956 and June 1957). In June 1957 the most remarkable of these high-latitude groups, Mount Wilson 12409, unique in some respects, transited the sun. It was first visible at the U.S. Naval Observatory on June 14, at the east limb, having formed on the invisible hemisphere. On that date only one member was visible, at longitude 80° E, latitude 39° S, with an area of 436 millionths of the sun's visible hemisphere. (The earth, placed at the sun's surface, would subtend an area of 42 millionths.) The next day the whole group came into view as a bipolar group with components separated by eight degrees in longitude and a total area of 824 millionths. In the course of its rotation across the disk the group separated in longitude, until on June 25 it was more than 25° in extent, a record for such a high latitude. This group is well shown in Plate I, where it is situated in the lower part of the picture. The range in latitude was from 42° to 32° S. The greatest area measured at the Naval Observatory was 2241 millionths on June 22. The mean area for the complete apparition was 1429 millionths, but the mean area for the group as a whole was 1687 millionths. This size exceeds by far that of any other group at such a high latitude, as revealed by a search through the records of the U.S. Naval Observatory, 1917-57, and the Photoheliographic Results of the Greenwich Observatory, 1874-1949, from which most of
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