Wilson effect (astronomy)

In astronomy, the Wilson effect is the perceived depression of a sunspot's umbra, or center, in the Sun's photosphere.

[1] Sunspots result from the blockage of convective heat transport by intense magnetic fields.

Sunspot occurrence follows an approximately 11-year period known as the solar cycle, discovered by Heinrich Schwabe in the 19th century.

In 1769, during solar cycle 2, Scottish astronomer Alexander Wilson, working at the Macfarlane Observatory, noticed that the shape of sunspots noticeably flattened as they approached the Sun's limb due to solar rotation.

[2] These observations were published in 1774[3] and showed that sunspots were features on the solar surface, as opposed to minor planets or objects above it.