太陽活動周期
Solar cycle 17 was the seventeenth solar cycle since 1755, when extensive recording of solar sunspot activity began. The solar cycle lasted 10.4 years, beginning in September 1933 and ending in February 1944. The maximum smoothed sunspot number (SIDC formula) observed during the solar cycle was 198.6 (April 1937), and the starting minimum was 5.8. During the minimum transit from solar cycle 17 to 18, there were a total of 269 days with no sunspots.