Celestial Tour: Shadow of the Moon

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The warped fabric of space that Einstein described is revealed by the shadow of the Moon.

Produced by the Space Telescope Science Institute’s Office of Public Outreach, in collaboration with NASA’s Universe of Learning and the Goddard Space Flight Center’s Heliophysics Science Division

All images, illustrations, video, and animations courtesy of NASA and STScI, except:

  • Total solar eclipse viewed from Oregon on August 21, 2017 video courtesy of Steve Sheridan 
  • Eclipse with star positions, May 29, 1919 photograph published by F. W. Dyson, A. S. Eddington, and C. Davidson, Philosophical Transactions of the Royal Society of London, Vol. 220, 1920
  • Coronal mass ejection, 2012 image courtesy of the Solar and Heliospheric Observatory (SOHO), NASA, and ESA
  • Solar prominence, May 29, 1919 photograph courtesy of the Royal Observatory Greenwich
  • Magnified deflected star, May 29, 1919 photograph courtesy of the Royal Observatory Greenwich
  • Total solar eclipse viewed from Australia, 1922 photograph courtesy of John Oxley Library, State Library of Queensland
  • Lick Observatory eclipse expedition in Western Australia, 1922 copyright the Museum of Applied Arts & Sciences
  • Total solar eclipse, 1936 film fragment by M. J. Leclerc, Société astronomique de France, courtesy of the Bibliothèque nationale de France
  • Astronomers viewing eclipse in Turkey, 1936 photograph courtesy of Atila Özgüç via Wikimedia Commons
  • Total solar eclipse viewed from Sudan, 1952 photograph by George Van Biesbroeck, courtesy of the University of Chicago Photographic Archive, apf6-02127, Special Collections Research Center, University of Chicago Library
  • George Van Biesbroeck and John Ladd viewing eclipse in Sudan, 1952 photograph copyright Chris Ware/Hulton Archive/Getty Images
  • Shadow of eclipse, 2016 video courtesy of the Cooperative Institute for Meteorological Satellite Studies (CIMSS), University of Wisconsin–Madison; based on images courtesy of Yasuhiko Sumida (from JMA, visiting CIMSS), data courtesy of JMA and NOAA
  • Music courtesy of Associated Production Music LLC


The northern atlantic ocean seen from high above. Text, In the spring of 1919 a team of astronomers organized an expedition from england to south america and africa. As the map pans south, a dotted line travels from the United Kingdom down to Africa, branching towards Sobral, Brazil in south america and Principe in the cape of africa. Text, Their goal, to observe a total solar eclipse, test albert einstein's general theory of relativity. The a line representing the eclipse path extends from the left side of the map to the right, crossing through both Sobral Brazil and Principe in Africa.
An animation of a dark moon moving over a white sun. Text, Shadow of the moon.
August 21, 2017, Oregon, United States. A halo of bright sunlight shines around the dark circle of the moon. Text, a solar eclipse occurs when the moon passes directly between earth and the sun. Light speeding from the sun is halted by the giant mass of rock blocking its path. Stars that are invisible during the day appear in the sky beside the darkened sun . May 29, 1919, sobral, brazil, 9 A M local time. Stars in the sky next to the eclipsed sun. Text, It was these background stars, not the eclipse itself, that the astronomers had traveled so far to see.
An animation of the earth and sun in space, with a star behind the sun. Text, Actual location of star. According to Einstein, light traveling through space past massive objects like the sun should curve more than previously calculated. A line moves from the star past the sun and towards earth, bending as it passes the sun.
A straight dotted line straight from earth to a point near the star. Text, apparent location of star. As a result, stars should look like they are in slightly different locations when the sun is close to them in the sky than at other times of year, when the sun is in a different part of the sky. View from earth, 1919 eclipse, months leading up to eclipse. A chart of Stars in the sky. Solid dots representing observed light and hollow dots representing the actual location. Text, but usually we cannot see the shifted stars next to the sun. during the day, the sun is too bright. The only time to record this shift and test einstein's theory is during a total solar eclipse.
By chance, the apparent sizes of the sun and moon in the sky are almost the same. A diagram of the small moon casting a shadow on earth as it passes in front of the sun. Lines appear showing a partial eclipse covering a large area on the earth and a total eclipse covering a very small area. Text, The Moon can mask the Sun completely.
January 27, 2012, coronal mass ejection, sun eclipsed by coronagraph, nasa's solar and heliospheric observatory. Some investigations of the sun, moon, earth and space itself are possible only when the sun is blocked completely. Plumes of pale cloud-like flames erupting from the edge of the sun, which is blocked by a circle. An animation of the moon orbiting the sun. Text, Eclipse occurs. Shadow passes through orbital plane. Scientists were eager to test Einstein's theory, but total solar eclipses occur only once every 18 months or so. The moon orbits earth on a plane that is tilted relative to earth's orbital plane. Eclipse does not occur, shadow does not pass through orbital plane. Most months, the moon's shadow passes above or below earth.
An antique map of south america and africa showing the path of totality, may 29, 1919. The path of the total eclipse. Text, As they made plans to test Einstein's theory, the scientists knew when and where the next suitable eclipse would occur. Sobral Brazil, 12:01 U T, Principe Africa, 14:16 U T. Years of observations and careful calculations make it possible to predict the motion of objects in the sky and the exact date, time, and path of the eclipse. As predicted, the moon's shadow fell over Sobral first and then sped eastward, reaching Principe 2 hours later. A photo of a black circular moon passing in front of the sun. Text, May 29, 1919, Sobral Brazil. In both locations, the astronomers took advantage of the five minutes of totality to photograph the eclipsed sun and surrounding sky. On returning to England several months later, the scientists analyzed their results. A blurry image of a white dot, apparent location of star. They carefully compared the apparent positions of the stars during the eclipse to the stars' actual positions, as photographed in the night sky at other times of year. Actual location of star near apparent location, a barely visible dot. Text, the observations of the 1919 eclipse, particularly those from Sobral, provided compelling evidence for Einstein's theory.
Since 1919 the investigation has been repeated many times with similar results. Photos of astronomers with telescopes at the 1922 eclipse australia, 1936 eclipse europe and asia, 1952 eclipse sudan. Text, The warped fabric of space that Einstein described is revealed by the shadow of the moon.
The dark circle of the Moon's shadow passes across the face of the earth. Text, Our universe is further illuminated with the shadow of each passing eclipse.