Evershed first detected this phenomenon in January 1909, whilst working at the Kodaikanal Solar Observatory in India,[3] when he found that the spectral lines of sunspots showed doppler shift.
The Evershed effect is common to every spectral line formed at a temperature below 105 K; this fact would imply a constant downflow from the transition region towards the chromosphere.
Of course, this is impossible, since if it were true, the corona would disappear in a short time instead of being suspended over the Sun at temperatures of million degrees over distances much larger than a solar radius.
Many theories have been proposed to explain this redshift in line profiles of the transition region, but the problem is still unsolved, since a coherent theory should take into account all the physical observations: UV line profiles are redshifted on average, but they show back and forth velocity oscillations at the same time.
In synthesis, the proposed mechanisms are: The effect was commemorated in a postage stamp issued in India on 2 December 2008.