Evershed Effect

A commemorative postage stamp on Centenary of the Discovery of the Evershed Effect (Radial Flow of Gas across the Photospheric Surface of Sunspots) :

India Stamp 2008, John Evershed, centenary, discovery, solar, SunIssued by India

Issued on Dec 2, 2008

Issued for : India Post is proud to issue commemorative postage stamp on centenary of the discovery of Evershed Effect.

Credits :
& FDC : Suresh Kumar
Cancellation : Alka Sharma

Type : Stamp, Mint condition

Colour : Multicolour

Denomination : 500 Paise

Stamps Printed : 0.4 Million

Printing Process : Wetoffset

Printer : Security Printing Press, Hyderabad

About : 

  • Solar eclipse of 1868 and 1871 played a fundamentally significant role in the development of astrophysics in India. The idea to establish a modern observatory at a hill station took roots. Physics Observatory at Kodaikanal, was the outcome of such an idea and was founded in 1899, which started functioning in 1899. John Evershed, one of the foremost solar astronomers of his time, spent his most fruitful research years at the Solar Physics Observatory in Kodaikanal, first as its Assistant Director (1907-1911) and then as the Director (1911-1923). He had distinguished himself as a prolific amateur solar observer, working in his own private observatory in Kenley, England, recording no less than 13,458 prominences between the years 1890 and 1905, and noting the changes in heliographic latitude during a solar cycle. The Kodaikanal appointment was his first as a professional astronomer. When John Evershed arrived in 1906, Kodaikanal already had some good solar instruments including a Cambridge Spectroheliograph. With his expertise and experience as an instrument builder, Evershed was able to improve upon these instruments and look at the Sun with great clarity. He started working on the spectrum of sunspots soon after.
  • In the early morning of January 5, 1909, on a day when the atmosphere was exceptionally steady and sky transparency was excellent, Evershed obtained Sunspot spectra which showed for the first time line displacements in the penumbral region indicating an outward radial flow of gases in the spots. Two days later, Evershed obtained more spectra which confirmed the discovery. The discovery has since been named after him and is known today as the Evershed Effect.
  • Earlier studies had concentrated on spots near the central meridian of the Sun. Evershed was the first to observe spots at various positions, up to 50 degrees, on either side of the central meridian. He found that the line displacements were more pronounced in the penumbral regions of the spots which are closer to the limb of the Sun. This clearly showed that the flow of the gases was radially outward parallel to the surface of the Sun. Evershed’s discovery is the forerunner of many important discoveries which connect the velocities and magnetic fields on the surface of the Sun, which has given rise to the entire field of solar magneto hydrodynamics. Evershed’s work established the reputation of Kodaikanal as one of the best solar observatories in the world. In 1913, Evershed visited Kashmir for three months and found the observing conditions in the Kashmir Valley excellent for solar work. He established a temporary observatory near Srinagar in 1915-16 obtaining very high-quality photographs of prominences and sunspots.
  • During the hundred years since Evershed’s discovery, our understanding of the solar phenomena and the solar-terrestrial relations has grown enormously. It has profoundly influenced diverse fields of science and great benefits have been derived from these studies. Solar space missions have further enriched our knowledge of the complex processes taking place on the solar surface and their impact on the interplanetary space and our terrestrial environment.
  • Text : As per the material provided by the proponent.

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