Show Summary Details

Page of

PRINTED FROM OXFORD REFERENCE (www.oxfordreference.com). (c) Copyright Oxford University Press, 2013. All Rights Reserved. Under the terms of the licence agreement, an individual user may print out a PDF of a single entry from a reference work in OR for personal use.

date: 18 January 2018

Evershed effect

Source:
A Dictionary of Astronomy
Author(s):

Ian Ridpath

Evershed effect 

An outward flow of gas in the penumbra of a sunspot, starting from the boundary with the umbra and moving radially out 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 the English astronomer John Evershed (1864–1956), who discovered it in 1909.