Celebrating the 20th century's most important experiment
Issued: 28 May 2009 by
Portuguese versions by AngolaPress and
Dr Robert Massey
Press and Policy Officer
Royal Astronomical Society
Tel: +44 (0)20 7734 3307
Mob: +44 (0)794 124 8035
In 1919, the Royal Astronomical Society (RAS) launched an expedition to the West African
island of Príncipe, to observe a total solar eclipse and prove or disprove Einstein's General Theory of Relativity.
Now, in a new RAS-funded expedition for the International Year of Astronomy (IYA 2009), scientists are back.
In 1919, the Royal Astronomical Society (RAS) launched an expedition to the West African island
of Príncipe, to observe a total solar eclipse and prove or disprove Einstein's General Theory of Relativity. Now, in
a new RAS-funded expedition for the International Year of Astronomy (IYA 2009), scientists are back.
Astronomers Professor Pedro Ferreira from the University of Oxford and Dr Richard Massey from the
University of Edinburgh, along with Oxford anthropologist Dr Gisa Weszkalnys, are paying homage to the original expedition
led by Sir Arthur Eddington and celebrating the 90th anniversary of one of the key discoveries of the 20th
Einstein first proposed his General Theory of Relativity in 1915. It describes how any massive
object, such as the Sun, creates gravity by bending space and time around it. Everything in that space is also bent: even
rays of light. Consequently, distant light sources, behind the massive object, can appear in a different position or look
brighter than they would otherwise.
The total eclipse of 29th May 1919 gave scientists the chance to test the theory for the first
time. Eddington travelled to Príncipe to observe the eclipse and measure the apparent locations of stars near the Sun. Heavy
clouds parted minutes before the eclipse and, with the Sun almost directly in front of them, the stars appeared to be
shifted from the positions that Eddington had recorded in Oxford 4 months earlier — direct evidence that our nearest
star shapes the space around it.
"This first observational proof of General Relativity sent shockwaves through the scientific
establishment," said Professor Ferreira. "It changed the goalposts for physics."
To mark the anniversary, in partnership with the International Astronomical Union, São
Toméan and Portuguese governments, the team will gather with local people for a series of public talks, the
installation of an exhibition in the capital Santo António, and the unveiling of a plaque at the plantation where the
original observation was made. Dr. Weszkalnys feels it "particularly important that in 2009, the International Year of
Astronomy, the dramatic role played in the history of science by a tiny island like Príncipe should not be
Eddington's 1919 measurement of the bending of light was used to determine the nature of
gravity. At the time, even Einstein saw no further uses. "But now that gravity is well understood," said Dr. Massey, "the
effect, known as 'gravitational lensing', has become one of our most powerful tools to study the Universe."
Gravitational lenses work in a similar way to ordinary glass lenses, focusing and magnifying
light — but on a huge scale. They enable astronomers like Dr Massey to see objects that are otherwise too far away or
faint for even the largest telescopes on Earth.
Dr Gisa Weszkalnys
University of Oxford
Dr Richard Massey
Institute for Astronomy, University of Edinburgh
Royal Observatory Edinburgh
Professor Pedro Ferreira
University of Oxford
Eleanor Gilchrist, PR Officer
Royal Observatory Edinburgh
Tel: +44 (0)131 668 8397
Príncipe eclipse expedition: http://www.1919eclipse.org/
São Tomé and Príncipe tourist board: http://www.turismo-stp.org/pages/en/
(and amusing) newspaper headlines from the time: http://www.1919eclipse.org/1919eclipse.php
The Plaque http://www.1919eclipse.org/images/posters/Plaque.png
map showing the location of Príncipe http://www.1919eclipse.org/principe.php
NOTES FOR EDITORS
THE ROYAL ASTRONOMICAL SOCIETY
The Royal Astronomical Society (RAS), founded in 1820, encourages and promotes the study of astronomy,
solar-system science, geophysics and closely related branches of science. The RAS organizes scientific meetings, publishes
international research and review journals, recognizes outstanding achievements by the award of medals and prizes, maintains
an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and
internationally. Its more than 3000 members (Fellows), a third based overseas, include scientific researchers in
universities, observatories and laboratories as well as historians of astronomy and others.
THE INTERNATIONAL YEAR OF ASTRONOMY 2009 (IYA 2009)
The International Year of Astronomy 2009 (IYA 2009) will be a global
celebration of astronomy and its contributions to society and culture. It is intended to stimulate worldwide interest not
only in astronomy, but in science in general, with a particular slant towards young people. IYA 2009 will mark the 400th
anniversary of the monumental leap forward that followed Galileo Galilei's first use of the telescope for astronomical
observations. In the UK the chair of IYA2009 is Professor Ian Robson, director of the UK Astronomy Technology Centre in
Edinburgh, and the co-ordinator for IYA 2009 activities is Steve Owens, also a UKATC employee. UK IYA 2009 activities are
jointly funded by the Royal Astronomical Society (www.ras.org.uk), the Institute of
Physics (www.iop.org) and the Science and Technology Facilities Council (www.stfc.ac.uk).
IYA 2009 UK home page http://www.astronomy2009.co.uk