This Day in History (23-Sep-1846) – Astronomers Discover Neptune

After first being sighted in the night sky by Galileo in 1612, it took well over two centuries for scientists to determine the bright object near Jupiter in the famous Italian’s notes was not a star.  Urbain Le Verrier and Johann Gottfried Galle, working together on the European continent, and John Couch Adams, making calculations independently in England, learned the heavenly body was actually the planet Neptune on September 23, 1846.

Alexis Bouvard, attempting to determine the orbits of the planets in 1821, realized the planet Uranus seemed to be swayed and theorized another large object nearby might be affecting it. Two decades later, Adams focused his energies on the same issue.  Unsatisfied with the limited data he had managed to gather, he made an inquiry with the Astronomer Royal, George Airy, in search of more information to help him with his search for a new planet.  Upon receiving a large number of observations in February 1844, he spent two-and-a-half years attempting to determine where this unknown celestial body might be.

At the same time, Le Verrier focused his attention on determining what Bouvard had found.  Unable to muster much in the way of interest, he published a series of estimates in June 1846.  Le Verrier, struggling to find scientists in his own country willing to pay attention and collaborate, wrote a letter to Galle at the Berlin Observatory detailing his findings.  Arriving on the morning of September 23, 1846, Le Verrier’s note proved to be the final catalyst to the discovery of Neptune.  After nightfall, Galle located the planet just one degree away from where Le Verrier had predicted it would be and 12 degrees away from Adams’ calculated location.  The eighth planet in Earth’s solar system had been officially discovered. After the discovery, there was rivalry between England and France about who should get credit for finding Neptune, Adams or Le Verrier. The international astronomy community agreed that the two astronomers should share credit for the discovery.

Late in 1846, the St. Petersburg Academy of Sciences pushed Le Verrier’s first suggestion for name — Neptune — to the fore.  Honoring the Roman god of the sea, it remains the farthest planet from the sun.