Hale's law

Magnetogram showing the opposite polarity of active regions from solar cycle 23 and 24

The solar magnetic field was first detected in 1909 by George Ellery Hale when he showed observationally that sunspots had strong, bipolar magnetic fields. With these observations, Hale was also able to describe how sunspot groups within the same heliospheric hemisphere shared the same leading polarity and that this pattern reversed across the equator. As solar cycle 14 transitioned into solar cycle 15, further observations were carried out by Hale and his collaborators revealing in 1919 that the magnetic polarity of sunspot pairs within both hemispheres reversed from one cycle to the next. These patterns became collectively known as Hale's polarity law, or simply Hale's law.[1][2]

Bipolar active regions that violate Hale's law are known as anti-Hale regions. The estimated relative number of anti-hale regions varies from 2 to 9%, due to how often anti-Hale regions are misidentified.[3]

Small, weak, ephemeral active regions violate Hale's law more frequently than average with a relative number around 40%. In contrast, only 4% of medium to large sized active regions violate Hale's law.[4][5] Additionally, anti-Hale regions, and small regions in general, tend to have an orientation angle, or tilt, that does not follow Joy's law.[6]

• Joy's law (astronomy)
• Spörer's law
• Solar cycle
• Active region
• Sunspot

• "The magnetic nature of sunspots | High Altitude Observatory". www2.hao.ucar.edu.