A History of Neptune’s Discovery
Galileo first discovered Neptune on December 28, 1612 but mistook it for a fixed star because it was in conjunction with Jupiter. On that date Neptune had stationed retrograde and thus its movement was undetectable by him. Galileo again observed Neptune on Jan 27, 1613 when Jupiter had turned retrograde, but due to the technology of his telescope he still thought it was a fixed star. Thus, he is not credited with its discovery. Remarkably, Galileo had invented his telescope only three years earlier in 1609 (astronomers celebrated last year as the 400th anniversary of his invention).
In 1821 astronomer Alexis Bouvard published what he thought to be Uranus’ orbit, but, when subsequent observations revealed significant deviations, he hypothesized that another planet’s gravitational pull was likely the culprit. Sir George Airy, the Astronomer Royal in England, corresponded with Bouvard about the orbit perturbations, and contemplated the immense difficulty in calculating the orbit of a hypothetical planet with the centuries of data collection needed for such a project. Sir Airy apparently considered the possibility that the Law of Gravity might not be valid at such enormous distances from the Sun.
In September of 1845 John Couch Adams, a mathematics student at Cambridge, calculated the hypothetical planet’s orbit, and sent his work to Sir Airy. The director of the Cambridge observatory, Professor Challis, wrote a letter of introduction for Adams to Sir Airy, but Adams never followed up with a confirmed appointment. Although Adams tried three times to meet with Sir Airy, twice he wasn’t there, and on the third occasion Adams was refused audience. Three weeks later Sir Airy asked Adams for clarification on his calculations, but Adams did not answer him for a year because he felt the answers to the questions were obvious.
Three eminent scholars of that age had a possible solution to the most important astronomical problem of their time, yet neither Professor Challis nor Sir Airy could be bothered to point their telescopes towards the heavens in search of Neptune’s illusory presence. Professor Challis felt it too difficult to locate a planet in deep space, and Sir Airy doubted the accuracy of the mathematical calculations.
In June 1846, astronomer Urbain Le Verrerier in France had independently come to his own conclusions about the orbit problem of Uranus but, like Adams, could not raise enough interest in his French colleagues to pursue the topic. Le Verrerier published his work and finally Sir Airy, noticing similarities in both Adams’ and Le Verrerier’s calculations, urged Professor Challis of Cambridge to search for the planet - he acquiesced, but thought himself unsuccessful.
Meanwhile, the persistent Le Verrerier, in order to circumvent official channels thwarting his efforts to find the hypothetical planet, contacted a friend who was a subordinate at the Berlin Observatory asking him to search for the planet. On the actual date of arrival of his letter, the evening of September 23, 1846, Neptune was discovered within 1 degree of where Le Verrerier had calculated it would be. It was approximately 12 degrees from where Adams’ had predicted. Later, Professor Challis of Cambridge realized that he had observed Neptune twice in August but because of his immense work load creating star charts he was unable to identify its location by comparing his finding with previous charts.
In the wake of Neptune’s discovery, both the French and the British wanted to claim credit for its discovery, but eventually the international community concluded that both nations were equally deserving. However, in 1998, there was an important discovery surrounding Neptune once again, the “Neptune Correspondences”. These were letters and unpublished research documents from Adams; important historical documents from the Royal Observatory in Greenwich that had been stolen by the astronomer Olin J. Eggen and kept secret for almost 30 years until their discovery immediately after his death in Chile.
Adams’ research papers, it turns out, had never been allowed to be reviewed by scholars at Cambridge - those who inquired about them had been told they were unavailable - and for good reason. It turns out his calculations were off by as much as twenty degrees. Some historians now believe that Adams does not deserve equal credit as co-discoverer of Neptune. It seems Sir Airy and subsequent astronomers conspired to keep England’s credit as co-discoverer.
The naming of Neptune contains intrigue as well. In England, Challis desired to name the planet Oceanus. While in France, falsely stating official approval by the French Bureau des Longitudes (yet another ruse), Le Verrerier claimed the right to name his discovery: Neptune. The next month, in October, Le Verrerier changed his mind and wanted the planet to be named after himself. His latest idea was met with great resistance and by December, 1846, the international community decided upon the name of Neptune due to its greenish color like the sea.
Although in later years Le Verrerier was named Director of the Paris Observatory, he suffered an immense personal defeat in having to share credit with Adams. In further machinations, Le Verrerier was removed from his position as Director by his fellow employees, who described him as a despot. He was subsequently reinstated after his successor died by drowning!