Solar cycle 18

{{Infobox Solar cycles

|cycle_num=18

|start_date=February 1944

|end_date=April 1954

|duration=10.2

|max_count=218.7

|max_count_date=May 1947

|min_count=12.9

|spotless_count=446

|prev_name=Solar cycle 17

|next_name=Solar cycle 19

|prev_dates=1933–1944

|next_dates=1954–1964

}}

Solar cycle 18 was the eighteenth solar cycle since 1755, when extensive recording of solar sunspot activity began.{{citation|doi=10.1023/A:1014296529097|year=2002|last1=Kane|first1=R.P.|title=Some Implications Using the Group Sunspot Number Reconstruction|journal=Solar Physics|volume=205|issue=2|pages=383–401|bibcode=2002SoPh..205..383K|s2cid=118144552}}{{cite web | title=The Sun: Did You Say the Sun Has Spots? | url=http://www.spacetoday.org/SolSys/Sun/Sunspots.html | publisher=Space Today Online | accessdate=12 August 2010}} The solar cycle lasted 10.2 years, beginning in February 1944 and ending in April 1954. The maximum smoothed sunspot number observed during the solar cycle was 218.7 (May 1947), and the starting minimum was 12.9.SIDC Monthly Smoothed Sunspot Number. "[http://sidc.oma.be/sunspot-data/]" During the minimum transit from solar cycle 18 to 19, there were a total of 446 days with no sunspots.Spotless Days. "[http://spaceweather.com/glossary/spotlessdays.htm?PHPSESSID=dli444kmrjgre0rjq6l86fv144]"{{cite web |url=https://science.nasa.gov/headlines/y2008/11jul_solarcycleupdate.htm|title=What's Wrong with the Sun? (Nothing)|date=11 July 2008|author=Dr. Tony Phillips|publisher=NASA|archive-url=https://web.archive.org/web/20080714032353/https://science.nasa.gov/headlines/y2008/11jul_solarcycleupdate.htm|archive-date=14 July 2008}}Solaemon's Spotless Days Page. "[http://users.telenet.be/j.janssens/Spotless/Spotless.html]"

Cycle 18 was characterized by "giant" sunspots.{{cite journal |last1=Dodson |first1=Helen W. |last2=Hedeman |first2=E. Ruth |last3=Mohler |first3=Orren C. |date=August 1974 |title=Comparison of activity in solar cycles 18, 19, and 20 |journal=Reviews of Geophysics |volume=12 |issue=3 |pages=329–341 |doi=10.1029/RG012i003p00329 |bibcode = 1974RvGSP..12..329D }} The recording of the 10.7 cm (2800 MHz) solar radio flux began partway during this cycle,{{cite book |last=Petersen |first=Edward |date=2012 |title=Single Event Effects in Aerospace |url=https://books.google.com/books?id=TS7_jjnL-3AC&pg=PA20 |publisher=Wiley |page=20 |isbn=978-1118084304 }} and values of the solar flux during this cycle turned out to be particularly high.