Evershed effect

The Evershed effect is the radially outward flow of gas across the photospheric surface of the sun from the penumbra of a sunspot inner boundary to the outer boundary of the penumbra.

The velocity of the flow is from 1 km per second at the boundary between umbra and penumbra to a maximum of 2 kilometers per second in the center of the penumbra.

The phenomenon was created by the British astronomer John Evershed (1864-1956) first observed in 1909, when he worked at the Kodaikanal Solar Observatory in India and examined the Doppler shift of the spectral lines in sunspots.