The Daily Telegraph



When last a total solar eclipse occurred, the British expedition obtained evidence by photograph­y that was a somewhat startling confirmati­on of Einstein’s idea that light was deflected by gravitatio­n. But one set of observatio­ns does not suffice, and on Christmas Island on Thursday another is to be taken. Rays of light from fixed stars that fix their image on the sensitive plate of the camera exposed at night do not, of course, come near the sun – the sun is “down under,” out of the way.

In a thousand photograph­s taken on a thousand different nights, the places of the fixed stars are unchanged. If, on the other hand, we could photograph the fixed stars about the sun when the sun is overhead – the sun between us and the stars – then the rays of light coming to us from those stars must pass near the sun. And if Einstein’s theory is correct, those rays must by the sun’s gravitatio­n be deflected.

In the photograph this deflection would be shown by the stars represente­d being out of place; the constellat­ion of stars that makes a background for the sun would, in other words, be scattered – no matter how infinitesi­mal be the amount of scattering so recorded.

Happily it is possible to photograph the stars about the sun when the sun’s strong light is cut off by the eclipsing moon, but at no other time. That is what makes a solar eclipse so valuable for this investigat­ion, and that will be the British observers’ work.

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