Solar cycle 4

Solar cycle 4 was the fourth solar cycle since 1755, when extensive recording of solar sunspot activity began.^[1][2] The solar cycle lasted 13.7 years, beginning in September 1784 and ending in May 1798 (thus overlapping the Dalton Minimum). The maximum smoothed sunspot number (monthly number of sunspots averaged over a twelve-month period) observed during the solar cycle was 141.2 (in February 1788), and the minimum was 3.2.^[3]

There are some recent speculations that cycle 4, the longest solar cycle since 1755, was actually two cycles, based on the appearance of new sunspots at high solar latitudes in 1793-1796 and a reconstruction of the sunspot butterfly diagram for cycles 3 and 4,^[4][5] although total sunspot numbers only show a single-peaked distribution.^[3]

See also

• Solar variation
• List of solar cycles

References

Solar cycles 18th century Solar cycle 1 (1755 March – 1766 June) Solar cycle 2 (1766 June – 1775 June) Solar cycle 3 (1775 June – 1784 September) Solar cycle 4 (1784 September – 1798 May) Solar cycle 5 (1798 May – 1810 December) 19th century Solar cycle 6 (1810 December – 1823 May) Solar cycle 7 (1823 May – 1833 November) Solar cycle 8 (1833 November – 1843 July) Solar cycle 9 (1843 July – 1855 December) Solar cycle 10 (1855 December – 1867 March) Solar cycle 11 (1867 March – 1878 December) Solar cycle 12 (1878 December – 1890 March) Solar cycle 13 (1890 March – 1902 February) 20th century Solar cycle 14 (1902 February – 1913 August) Solar cycle 15 (1913 August – 1923 August) Solar cycle 16 (1923 August – 1933 September) Solar cycle 17 (1933 September – 1944 February) Solar cycle 18 (1944 February – 1954 April) Solar cycle 19 (1954 April – 1964 October) Solar cycle 20 (1964 October – 1976 June) Solar cycle 21 (1976 June – 1986 September) Solar cycle 22 (1986 September – 1996 May) Solar cycle 23 (1996 May – 2008 January) 21st century Solar cycle 24 (2008 January – present) List of solar cycles