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Solar cycle 4 was the fourth solar cycle since 1755, when extensive recording of solar sunspot activity began. The solar cycle lasted 13.6 years, beginning in September 1784 and ending in April 1798 (thus overlapping the Dalton Minimum). The maximum smoothed sunspot number observed during the solar cycle was 235.3 (in February 1788), and the starting minimum was 15.9.

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, although total sunspot numbers only show a single-peaked distribution.

See also

• List of solar cycles

References

1. Kane, R.P. (2002). "Some Implications Using the Group Sunspot Number Reconstruction". Solar Physics 205(2), 383–401.
2. "The Sun: Did You Say the Sun Has Spots?". Space Today Online. Retrieved 12 August 2010.
3. ^ SIDC Monthly Smoothed Sunspot Number. ""
4. Usoskin, I. G.; Mursula, K.; Arlt, R.; Kovaltsov, G. A. (2009). "A Solar Cycle Lost in 1793–1800: Early Sunspot Observations Resolve the Old Mystery". The Astrophysical Journal. 700 (2): L154. arXiv:0907.0063. Bibcode:2009ApJ...700L.154U. doi:10.1088/0004-637X/700/2/L154.
5. "Centuries-old sketches solve sunspot mystery", New Scientist, 1 August 2009, p. 10.

v t e Solar cycles
18th century	1740–1759 Solar cycle 1 (1755 Feb – 1766 Jun) 1760–1779 Solar cycle 2 (1766 Jun – 1775 Jun) Solar cycle 3 (1775 Jun – 1784 Sep) 1780–1799 Solar cycle 4 (1784 Sep – 1798 Apr) Solar cycle 5 (1798 Apr – 1810 Aug)
19th century	1800–1819 Solar cycle 6 (1810 Aug – 1823 May) 1820–1839 Solar cycle 7 (1823 May – 1833 Nov) Solar cycle 8 (1833 Nov – 1843 Jul) 1840–1859 Solar cycle 9 (1843 Jul – 1855 Dec) Solar cycle 10 (1855 Dec – 1867 Mar) 1860–1879 Solar cycle 11 (1867 Mar – 1878 Dec) Solar cycle 12 (1878 Dec – 1890 Mar) 1880–1899 Solar cycle 13 (1890 Mar – 1902 Jan)
20th century	1900–1919 Solar cycle 14 (1902 Jan – 1913 Jul) Solar cycle 15 (1913 Jul – 1923 Aug) 1920–1939 Solar cycle 16 (1923 Aug – 1933 Sep) Solar cycle 17 (1933 Sep – 1944 Feb) 1940–1959 Solar cycle 18 (1944 Feb – 1954 Apr) Solar cycle 19 (1954 Apr – 1964 Oct) 1960–1979 Solar cycle 20 (1964 Oct – 1976 Mar) Solar cycle 21 (1976 Mar – 1986 Sep) 1980–1999 Solar cycle 22 (1986 Sep – 1996 Aug) Solar cycle 23 (1996 Aug – 2008 Dec)
21st century	2000–2019 Solar cycle 24 (2008 Dec – 2019 Dec) Solar cycle 25 (2019 Dec – present)
List of solar cycles List of solar storms List of solar maxima and minima

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