Evershed effect

A Dictionary of Astronomy | 1997 | 619 words | Copyright

Evershed effect An outward flow of gas from the centre of a sunspot, proceeding from the umbra through the penumbra, and sometimes a little beyond it. The effect can be observed spectroscopically, particularly for spots near the solar limb, but may also be visible as outward-moving facular points, forming a so-called moat. The maximum outflow velocity is about 2 km/s. There is an inverse Evershed flow at higher altitudes, in which the flow (up to 20 km/s) is directed both inwards and downwards towards the sunspot. The effect is named after its discoverer, the English astronomer John Evershed (1864–1956).

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