International Year of Astronomy 2009
UNESCO International Astronomical Union      

Celebrating the 1919 Eclipse at Príncipe

In May 1919, Sir Arthur Eddington and the Royal Astronomical Society launched an historic expedition to observe a total solar eclipse. Historians now recognise this expedition as a major achievement of 20th century science.

The eclipse was visible from equatorial regions on both sides of the Atlantic; Eddington sent one team to Sobral in Brazil, and went himself went to the African island of Príncipe. Stars in the Hyades cluster were behind the sun during the eclipse, and were appeared to shift from their true positions by 1.75 arcseconds. This gravitational deflection of light by the sun's mass provided the first experimental verification of Albert Einstein's theory of general relativity. Eddington's persistence and scientific conviction in pursuing the expedition were largely responsible for Einstein's fame (M. Stanley, 2007). And although neither Einstein nor Eddington initially foresaw practical applications for the effect known as gravitational lensing, ninety years later it has emerged as the most promising probe of our Universe.

For the benefit of the local population and international visitors, this International Year of Astronomy special project will celebrate the expedition's 90th anniversary: to explain the historic significance of the site, and the way in which gravitational lensing is shaping contemporary scientific understanding of the Universe.


In collaboration with the local government and population, and with international institutional support, we shall

  • Unveil an interpretative plaque in a ceremony on the 29 May anniversary of the eclipse, at Roça Sundy, the former colonial plantation where Eddington took measurements.
  • Give popular lectures on the science and history underpinning the expedition, in Príncipe, in the capital of São Tomé, and in Lisbon.
  • Install an illustrative exhibition of the progress made in gravitational lensing from 1919 to the present day in São Tomé.

Our activities will be accompanied and complemented by a local educational campaign carried out by the government of São Tomé e Príncipe and other national and international activities. We hope to establish local recognition of the importance of astronomy, particularly in young people. The project will also help preserve a site of significant cultural value, as a point of attraction beneficial to the emerging tourist industry of São Tomé and Príncipe, now an independent island state.

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