The Discovery of Neptune

The planets of the Solar System are familiar to us, but a few centuries ago, people did not know they existed. Their discovery has been gradual. On 23 September, we celebrate 179 years since the discovery of Neptune. But what was crucial was that it was not discovered by chance, but by mathematical calculations.

The search for the eighth planet

In 1781, the planet Uranus was discovered. Since then, astronomers have been studying it and have come to the conclusion that the gravitational force of another body is acting on it. It took several decades for major advances to be made. Independently, the French astronomer Urbain Jean Joseph Le Verrier and the British astronomer John Couch Adams predicted the existence and position of the planet Neptune. This was an important event, as for the first time the planet was not discovered by chance, but through mathematical calculations. It became the eighth in the sequence.

The day the boundary fell

Observatories were initially reluctant to accept their results. Progress was only made by Le Verrier, who sent a letter to the German astronomer Johann Gottfried Galle giving the exact coordinates of Neptune. On the evening of 23 September 1846, he and his student Heinrich d’Arrest began their search. And indeed, they made an unprecedented discovery. They discovered the eighth planet less than a degree from its predicted position.

After the official discovery, it turned out that Neptune had been observed by several astronomers before, such as Galileo Galilei. But because of its slow motion, no one recognized it as a planet.

Efforts to take credit

As soon as the news of the discovery of Neptune went around the world, a great sensation was created around the event. However, a dispute arose over the primacy and the credit. British astronomer John Couch Adams, who had worked on his own calculations several years earlier, was met with rejection from the Greenwich Observatory, the Cambridge Observatory and astronomer George Biddell Airy. When Airy learned of the discovery of Neptune, however, he tried to give credit to England, although he rejected his colleague’s theory.

A dispute ensued as to whether France or England was the first. Adams himself, however , took a non-conflicting view and praised Le Verrier’s achievement. In his book he explained the chronology of his own findings and stated his feelings about the discovery of Neptune.

“I mention these dates only to show that I arrived at my results independently and before the publication of Mr. Le Verrier’s work, and not with the intention of interfering with his legitimate claim to the honors of discovery, for there is no doubt that his researches were first published in the course of that work, and led to the actual discovery of the planet by Dr. Gall, so that the above facts cannot in the least detract from the credit due to Mr. Le Verrier,” wrote Adams.

Neptune and its secrets

Although Neptune was discovered in 1846, it was not until the 20th century that concrete information about it was discovered. For a long time it was shrouded in mystery. It wasn’t until the Voyager 2 spacecraft made its 1989 flyby that new knowledge was brought about.

The impact on further exploration

The discovery of Neptune triggered another wave of searches for planets and other celestial bodies. The mathematical method that allowed Neptune to be found inspired and was used. The 1930s saw the discovery of Pluto, a dwarf planet that was previously thought to be the ninth planet.