Beck, J. G.; Giles, P. (10 March 2005). "Helioseismic Determination of the Solar Rotation Axis". The Astrophysical Journal. 621 (2): L153–L156. Bibcode:2005ApJ...621L.153B. doi:10.1086/429224.
Bartels, J. (1934), "Twenty-Seven Day Recurrences in Terrestrial-Magnetic and Solar Activity, 1923–1933", Terrestrial Magnetism and Atmospheric Electricity, 39 (3): 201–202a, Bibcode:1934TeMAE..39..201B, doi:10.1029/TE039i003p00201
Beck, J. G.; Giles, P. (10 March 2005). "Helioseismic Determination of the Solar Rotation Axis". The Astrophysical Journal. 621 (2): L153–L156. Bibcode:2005ApJ...621L.153B. doi:10.1086/429224.
Bartels, J. (1934), "Twenty-Seven Day Recurrences in Terrestrial-Magnetic and Solar Activity, 1923–1933", Terrestrial Magnetism and Atmospheric Electricity, 39 (3): 201–202a, Bibcode:1934TeMAE..39..201B, doi:10.1029/TE039i003p00201