Neptune, the 8th planet in our solar system, known as the blue giant (derived from the Roman myth of the God of the Sea) is the farthest planet from the sun. Its days are 16 hours and 6.7 minutes long; it has a diameter of 49,500 kilometres and 13 moons. The story of it’s discovery is a historically prestigious one, acting as a keystone for previous paradigms about our solar system.
Many times Neptune was observed without being recognised as a planet but as a star. First by famous Italian astronomer Galileo (1564-1642), on 28th December who at the time was observing Jupiter and recorded Neptune as an 8th magnitude star [i]. In 1795 a French astronomer Lalande (1732-1807) recorded it twice, on 8th and 10th May, but still believed it to be a star. Then on 14th July 1830 Neptune was again recorded as a star by John Hershel
French astronomer Delambres (1749-1822) noted for astronomical computations published in 1792 Tables du Soleil, de Jupiter, de Saturne, d'Uranus et des satellites de Jupiter, in which he published tables for the orbits of the Sun, Jupiter, Saturn and Uranus. Some of these tables however were incorrect and it was Bouvard who after publishing his tables of orbits of Jupiter and Saturn in 1808 decided he would then go on and correct Delambres tables. Alexis Bouvard, a French astronomer found that the observations did not fit, but could not explain it so went on anyway to publish his tables of the orbits of Uranus in 1821 but also writing ‘I leave it to the future the task of discovering whether the difficulty of reconciling [the data] is connected with the ancient observations, or whether it depends on some foreign and unperceived cause which may have been acting upon the planet.’ [iii] It was this that began Bouvard’s journey of discovery of Neptune.
Neptune was not first discovered by telescope, but predicted through mathematical calculations based on Newtonian laws, and the unorthodox orbit of the planet Uranus. John Couch Adams, a Cambridge mathematician suggested that the gravitational influence of an unknown body could explain these inconsistent orbits, and made calculations as to where this body may be within our solar system. He then took his calculations to the Royal Observatory, to present them to Sir George Airy. Despite Adams’ certainty, his calculations were ignored until similar predictions were made by a French mathematician, Joseph le Verrier. When Airy did take action, he instilled the help of Professor James Challis of Cambridge University [iv]. On September 23rd, 1846, Johann Gottfried Galle, (Berlin Observatory) and Louis d’Arrest (student of astronomy), were the first people to observe Neptune and recognise it not as a star, but as a body within our solar system. They found the new planet using predictions made by Adams and Joseph le Verrier, the latter of which, was only 1 degree off Neptune’s actual location [v].
Neptune’s discovery was not without problems however, in fact, the reason why Neptune was discovered in the first place was due to problems with the predicted orbits of the planet Uranus. A highly prominent problem was the fact that Neptune departs from the predicted orbit quickly, so the planet would not have been found if Galle and d’Arrest had begun their search later [vi]. The credit for discovering the planet was awarded to both Le Verrier and Adams, but not without some controversy after Airy and Challis realised they had let the French and Germans beat them to the discovery.
It is evident that the discovery of Neptune is creditable to a handful of people, including Galle and d’Arrest for actually observing the planet on the 23rd of September 1846, Adams and Le Verrier for their mathematical calculations, and even Newton, as the planets discovery was based around his Laws. However, who should get the credit is widely disputed, as Challis did observe Neptune four times without realising it prior to 23rd of September 1846.
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