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Updated: June 17, 2025
The frequency of the Aurora Borealis was found by Wolf to follow the same period. In fact, it is closely allied in its cause to terrestrial magnetism. Wolf also collected old observations tracing the periodicity of sun-spots back to about 1700 A.D. Spoerer deduced a law of dependence of the average latitude of sun-spots on the phase of the sun-spot period.
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