It is named after George Ellery Hale and Seth Barnes Nicholson, whose observations of active-region magnetic fields led to the law's formulation in the early 20th century.
[1] With these observations, Hale also noted that the majority of sunspot groups within the same northern or southern solar hemisphere shared the same leading polarity and that this pattern reversed across the equator.
[5][6] Small, weak, ephemeral active regions violate Hale's law more frequently than average with a relative number around 40%.
[7][8] Furthermore, anti-Hale regions—and small regions in general—tend to have an orientation angle, or tilt, that does not follow Joy's law and have been found to be more prevalent during solar minima.
[13] Hale's law has important implications for the Sun's internal magnetic field and the dynamo that drives it.