Solar cycle 20 explained

Cycle Num:20
Start Date:October 1964
End Date:March 1976
Duration:11.4
Max Count:156.6
Max Count Date:November 1968
Min Count:14.3
Spotless Count:272
Prev Name:Solar cycle 19
Next Name:Solar cycle 21
Prev Dates:1954–1964
Next Dates:1976–1986

Solar cycle 20 was the twentieth solar cycle since 1755, when extensive recording of solar sunspot activity began.[1] 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.[2] During the minimum transit from solar cycle 20 to 21, there were a total of 272 days with no sunspots.[3] [4] [5]

Comparison with other cycles shows that geomagnetic activity during the declining phase of cycle 20 (1973–1975) was unusually high.[6] Heavy solar activity was a factor in causing the earlier-than-expected atmospheric reentry of Skylab in 1979.[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]

August 1972 solar storm

See main article: August 1972 solar storm. 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.[9]

See also

Notes and References

  1. Web site: The Sun: Did You Say the Sun Has Spots? . Space Today Online . 12 August 2010.
  2. SIDC Monthly Smoothed Sunspot Number. "http://sidc.oma.be/sunspot-data/"
  3. Spotless Days. "http://spaceweather.com/glossary/spotlessdays.htm?PHPSESSID=dli444kmrjgre0rjq6l86fv144"
  4. Web site: What's Wrong with the Sun? (Nothing). https://web.archive.org/web/20080714032353/https://science.nasa.gov/headlines/y2008/11jul_solarcycleupdate.htm. dead. 14 July 2008. 11 July 2008. Dr. Tony Phillips. NASA.
  5. Solaemon's Spotless Days Page. "http://users.telenet.be/j.janssens/Spotless/Spotless.html"
  6. 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 . 10.1029/JA082i022p03311 . 1977JGR....82.3311G .
  7. Book: Benson. Charles Dunlap. William David. Compton. amp . 1983 . Living and Working in Space: A History of Skylab . NASA Scientific and Technical Information Office. SP-4208. 8114293. 362–363.
  8. Book: Miroshnichenko, Leonty . 2001 . Solar Cosmic Rays . Springer . 395 . 0792369289 .
  9. Knipp . Delores J. . B. J. Fraser . M. A. Shea . Margaret Shea (scientist). D. F. Smart . On the Little-Known Consequences of the 4 August 1972 Ultra-Fast Coronal Mass Ejecta: Facts, Commentary and Call to Action . Space Weather . 16 . 2018 . 11 . 10.1029/2018SW002024 . free . 2018SpWea..16.1635K . 1635–1643 .