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brightness of at least 2.5 (on a linear scale 1-5, 5=flare) and has an extent of at least five heliographic degrees.
# It contains plage that is bright near the west limb and is suspected of growing.

The region numbers reached 10,000 in July 2002. However, the SWPC continued using 4-digits, with the inclusion of leading zeros.

Magnetic field

Mount Wilson magnetic classification

The Mount Wilson magnetic classification system, also known as the Hale magnetic

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