太陽活動周期
Solar cycle 9 was the ninth solar cycle since 1755, when extensive recording of solar sunspot activity began. The solar cycle lasted 12.4 years, beginning in July 1843 and ending in December 1855. The maximum smoothed sunspot number (SIDC formula) observed during the solar cycle was 219.9 (February 1848), and the starting minimum was 17.6. During the solar cycle minimum transit from solar cycle 9 to solar cycle 10, there were a total of 655 days with no sunspots.