Dodson, Helen W.; Hedeman, E. Ruth; Mohler, Orren C. (August 1974). "Comparison of activity in solar cycles 18, 19, and 20". Reviews of Geophysics. 12 (3): 329–341. Bibcode:1974RvGSP..12..329D. doi:10.1029/RG012i003p00329.
Dodson, Helen W.; Hedeman, E. Ruth; Mohler, Orren C. (August 1974). "Comparison of activity in solar cycles 18, 19, and 20". Reviews of Geophysics. 12 (3): 329–341. Bibcode:1974RvGSP..12..329D. doi:10.1029/RG012i003p00329.