Both theory and observations are part of science, and they are tied together in a kind of cycle. A very clear example was the prediction of Einstein that a source of gravity (such as a star) would bend light passing nearby. An expedition was organised in 1919 to record the positions of stars around the Sun during a solar eclipse. The observation of star positions showed that the apparent star positions close to the Sun were changed slightly from their normal expected positions. In effect, the light passing the Sun was pulled towards the sun by gravitation. This confirmed predictions of gravitational lensing made by Albert Einstein in the general theory of relativity, published in 1915. This was the first solid evidence in favour of Einstein's theory.