Astronomy:Solar cycle 15

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Solar cycle 15
Kraus slunce 1926-01-23.jpg
Sunspots recorded during solar cycle 15 (23 January 1923).
Sunspot data
Start dateJuly 1913
End dateAugust 1923
Duration (years)10.1
Max count175.7
Max count monthAugust 1917
Min count2.5
Spotless days534
Cycle chronology
Previous cycleSolar cycle 14 (1902–1913)
Next cycleSolar cycle 16 (1923–1933)

Solar cycle 15 was the fifteenth solar cycle since 1755, when extensive recording of solar sunspot activity began.[1][2] The solar cycle lasted 10.1 years, beginning in July 1913 and ending in August 1923. The maximum smoothed sunspot number (SIDC formula) observed during the solar cycle was 175.7 (August 1917), and the starting minimum was 2.5.[3] During the minimum transit from solar cycle 15 to 16, there were a total of 534 days with no sunspots.[4][5][6]


Geomagnetic storms in March 1918, August 1919, October 1919, and March 1920 affected telegraph lines, while a solar flare on 13 May 1921 also affected rail signal and switching equipment, in what was known as the "New York Railroad Storm."[7]


A major geomagnetic storm during 13–15 May 1921 caused damage in communication systems and aurora displays in much of the eastern United States.[8]

See also


  1. Kane, R.P. (2002), "Some Implications Using the Group Sunspot Number Reconstruction", Solar Physics 205 (2): 383–401, doi:10.1023/A:1014296529097, Bibcode2002SoPh..205..383K 
  2. "The Sun: Did You Say the Sun Has Spots?". Space Today Online. Retrieved 12 August 2010. 
  3. SIDC Monthly Smoothed Sunspot Number. "[1]"
  4. Spotless Days. "[2]"
  5. Dr. Tony Phillips (11 July 2008). "What's Wrong with the Sun? (Nothing)". NASA. 
  6. Solaemon's Spotless Days Page. "[3]"
  8. Storms, Solar (28 July 2017). "Space Weather Newspaper Archives". 

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