Solar cycle 4

Solar cycle 4
Sunspot Data
Start date	September 1784
End date	May 1798
Duration (years)	13.7
Max count	141.2
Max count month	February 1788
Min count	3.2
Cycle chronology
Previous cycle	Solar cycle 3 (1775-1784)
Next cycle	Solar cycle 5 (1798-1810)

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

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.