Measuring the distances to stars



For many centuries it was assumed that the stars resided in a heavenly sphere surrounding the Earth, which was thought to lay at the centre of the Universe. When Galileo found evidence that not all heavenly bodies orbited the Earth, he gave his support to the Copernicus model that placed the Sun, not the Earth, at the centre. But, amongst the objections to this heliocentric model was the one that the stars did not appear to move when viewed from different parts of Earth’s suggested orbit.


When a foreground object is viewed from two different positions it appears to move against the background. For example, in the diagram below the foreground tree at C is viewed from two different positions, A and B. From position A the tree at C appears to lie in front of a gap between two background trees. But, from position B the tree…

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