Solar cycle 20

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Solar cycle 20
Solar magnetogram from solar cycle 20 (1974).
Sunspot data
Start dateOctober 1964
End dateMarch 1976
Duration (years)11.4
Max count156.6
Max count monthNovember 1968
Min count14.3
Spotless days272
Cycle chronology
Previous cycleSolar cycle 19 (1954–1964)
Next cycleSolar cycle 21 (1976–1986)
One of the largest solar prominences ever recorded, from solar cycle 20 (19 December 1973).[1]

Solar cycle 20 was the twentieth solar cycle since 1755, when extensive recording of solar sunspot activity began.[2][3] The solar cycle lasted 11.4 years, beginning in October 1964 and ending in March 1976. The maximum smoothed sunspot number observed during the solar cycle was 156.6 (November 1968), and the starting minimum was 14.3.[4] During the minimum transit from solar cycle 20 to 21, there were a total of 272 days with no sunspots.[5][6][7]

Comparison with other cycles shows that geomagnetic activity during the declining phase of cycle 20 (1973–1975) was unusually high.[8] Heavy solar activity was a factor in causing the earlier-than-expected atmospheric reentry of Skylab in 1979.[9]

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.[10]

August 1972 solar storm[edit]

An extremely active active region, McMath 11976, produced a historic series of solar flares and coronal mass ejections (CMEs) in August 1972. One CME traveled to Earth in a record low of 14.6 hours and produced a strong geomagnetic storm that caused widespread electrical and communications grid disturbances and the accidental detonation of numerous U.S. Navy magnetic sea mines in North Vietnam.[11]

See also[edit]


  1. ^ Martin, James. "NASA celebrates the 40th anniversary of Skylab (pictures)". CNET. Retrieved 19 March 2022.
  2. ^ Kane, R.P. (2002), "Some Implications Using the Group Sunspot Number Reconstruction", Solar Physics, 205 (2): 383–401, Bibcode:2002SoPh..205..383K, doi:10.1023/A:1014296529097
  3. ^ "The Sun: Did You Say the Sun Has Spots?". Space Today Online. Retrieved 12 August 2010.
  4. ^ SIDC Monthly Smoothed Sunspot Number. "[1]"
  5. ^ Spotless Days. "[2]"
  6. ^ Dr. Tony Phillips (11 July 2008). "What's Wrong with the Sun? (Nothing)". NASA. Archived from the original on 14 July 2008.
  7. ^ Solaemon's Spotless Days Page. "[3]"
  8. ^ 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.
  9. ^ Benson, Charles Dunlap & Compton, William David (1983). Living and Working in Space: A History of Skylab. NASA Scientific and Technical Information Office. p. 362–363. OCLC 8114293. SP-4208.
  10. ^ Miroshnichenko, Leonty (2001). Solar Cosmic Rays. Springer. p. 395. ISBN 0792369289.
  11. ^ Knipp, Delores J.; B. J. Fraser; M. A. Shea; D. F. Smart (2018). "On the Little‐Known Consequences of the 4 August 1972 Ultra‐Fast Coronal Mass Ejecta: Facts, Commentary and Call to Action". Space Weather. 16: 1635–1643. Bibcode:2018SpWea..16.1635K. doi:10.1029/2018SW002024.