Biography: James Bradley was the third Astronomer Royal at the Greenwich Observatory in London and responsible for two significant astronomical discoveries described as 'the most brilliant and useful of the century' by the director of the Paris Observatory Jean Baptiste Joseph Delambre.
Early on in his career Bradley worked with fellow astronomer Samuel Molyneux on how to measure the change in a star's position from earth, in an effort to provide definitive proof that the earth revolved around the sun. While repeating Robert Hooke's experiments to measure the star Gamma Draconis in 1725, Bradley realized the star's movement was due to aberration of light, the result of the finite speed of light combining with the earth moving through its orbit in space .
Bradley's other major discovery was the nutation of the earth, its uneven wobbling, resulting from the gravitational pull of the moon. Bradley reported these findings to the Royal Society and was awarded the Copley medal for it in 1748.
In 1742 Bradley succeeded Edmond Halley becoming the 3rd Astronomer Royal and head of the Greenwich Royal Observatory.
- 1744-12-31 English astronomer James Bradley announces discovery of Earth's nutation motion (wobble)
- 1747-02-14 Astronomer James Bradley presents his discovery of the wobbling motion of the Earth on its axis to the Royal Society, London