Halley, Comets and Newton
The definitive biographies of Isaac Newton and Edmond Halley are:
Never at Rest, A Biography of Isaac Newton, Richard S. Westfall, Cambridge University Press, 1980
In the Presence of the Creator, Isaac Newton & his Times, Gale E. Christianson, The Free Press, 1984
Edmond Halley, Charting the Heavens and the Seas, Alan Cook, Oxford, 1998.
Newton biographical link.
Halley biographical link
This link provides historical background for orbits and gravitation.
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