Professor David Jamieson, Head of the School of Physics at the University of Melbourne, says examination of the notebooks of Galileo reveal that the Italian scientist probably discovered Neptune over 200 years before its officially-listed discovery date.

In 1612 and 1613, Galileo made extensive observations of the moons of Jupiter, and noted the position of a nearby object that is now known, through computer simulation of astronomical positions as they would have been at the time, to have been Neptune. Galileo also noted that the faint object moved relative to a star that appeared close to it in the sky, something that he knew indicated that he was observing a planet and not another star.

Dr. Jamieson's findings were presented at the 2009 July Lectures in Physics program at the University of Melbourne.