Now it is the practice of astronomers to assume that brightness falls off inversely with the square of the "distance" of an object—as it would do in … - Howard P. Robertson

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Now it is the practice of astronomers to assume that brightness falls off inversely with the square of the "distance" of an object—as it would do in Euclidean space, if there were no absorption... We must therefore examine the relation between this astronomer's "distance" <math>d</math>... and the distance <math>r</math> which appears as an element of the geometry.