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Commemorating the Discovery of the Evershed Effect

The year 2009 marks one hundred years of the discovery of Evershed Effect in 1909 at the Kodaikanal Observatory which is one of the major findings made in solar physics from Indian soil. This was in fact the first astrophysical observation of interaction between plasma and magnetic field and has played an important role in our understanding of the physical properties of sunspots and the evolution of solar activity. John Evershed obtained spectra of a sunspot on January 5 and January 7, 1909, in order to determine the gas pressure in the sunspots. He found that the spectral lines were minutely displaced in the spectrum of penumbral region. Although astronomers had observed sunspots since long such a shift of spectral lines was detected for the first time by Evershed. From these observations he concluded that the peculiar behaviour is due to the Doppler effect. It indicated radial outflow of solar plasma in sunspots parallel to the solar surface. Much work has been done since then on this phenomenon. The Indian Institute of Astrophysics commemorated the discovery with an international conference entitled 'Magnetic Coupling between the Interior and the Atmosphere of the Sun', during Dec 2-5, 2008.


To mark the discovery, a commemorative stamp and a first day cover on the Evershed Effect were released in a special function at the Institute on Dec 2, 2008 by Shri M P Rajan, Chief Post Master General, Karnataka. The Stamp and the Cover are a tribute and beautifully bring forth the celebrated discovery.