Wilson effect


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Wilson effect

(wil -sŏn) The apparent displacement of the umbra of a sunspot relative to the penumbra as the spot is carried by the Sun's rotation from the east to the west limb of the disk. For a symmetrical sunspot, the side of the penumbra closest to the center of the disk is more foreshortened than that toward the limb. This was first interpreted as implying that the spot is a depression, but it is now known that the opacity of the umbra is less than that of the penumbra and that this also contributes to the effect.

Wilson effect

[′wil·sən i‚fekt]
(astronomy)
An effect in which the penumbra of a sunspot appears narrower in the direction toward the sun's center than in the direction toward the sun's limb.