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.
References in periodicals archive ?
But at the time the Danny Wilson effect hadn't yet been fully felt.
Since these models have long deprived the Sun of a true surface [2,29], they cannot rest upon geometrical arguments to account for the Wilson effect [35] and must have recourse to explanations based on optical depth (e.
The Wilson effect was established at the end of the 18th century [35].