Solar cycle 20

Solar cycle 20
Solar magnetogram from solar cycle 20 (1974).
Sunspot Data
Start date	October 1964
End date	June 1976
Duration (years)	11.7
Max count	110.6
Max count month	November 1968
Min count	12.2
Spotless days	272
Cycle chronology
Previous cycle	Solar cycle 19 (1954-1964)
Next cycle	Solar cycle 21 (1976-1986)

One of the largest solar flares ever recorded, from solar cycle 20 (19 December 1973).

Solar cycle 20 was the twentieth solar cycle since 1755, when extensive recording of solar sunspot activity began.^[1][2] The solar cycle lasted 11.7 years, beginning in October 1964 and ending in June 1976. The maximum smoothed sunspot number (monthly number of sunspots averaged over a twelve-month period) observed during the solar cycle was 110.6 (November 1968), and the minimum was 12.2.^[3] There were a total of 272 days with no sunspots during this cycle.^[4][5][6]

Comparison with other cycles shows that geomagnetic activity during the declining phase of cycle 20 (1973–1975) was unusually high.^[7]

Data from solar cycle 20 was used to build the K-1974 solar proton fluence model, used for planning space missions during solar cycle 21.^[8]

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. Spotless Days. ""
5. What's Wrong with the Sun? (Nothing) more information: Spotless Days. ""
6. Solaemon's Spotless Days Page. ""
7. Gosling, J. T.; Asbridge, J. R.; Bame, S. J. (1 August 1977). "An unusual aspect of solar wind speed variations during solar cycle 20". Journal of Geophysical Research 82 (22): 3311–3314. Bibcode:1977JGR....82.3311G. doi:10.1029/JA082i022p03311.
8. Miroshnichenko, Leonty (2001). Solar Cosmic Rays. Springer. p. 395. ISBN 0792369289.