Math Found Neptune!

Students will often ask "What is math used for in real life"? and I think they would be surprised to hear that scientists knew about Neptune before it was ever seen by a telescope.  It was the first planet to be discovered using mathematical calculations.

Imagine the scene.  Three different scientists, all working independently, all using calculations only, discovered Neptune in 1846.  Since they all made the discovery at about the same time, it lead to an international dispute as to which one would get credit.

Neptune is a planet that cannot be seen with the naked eye from earth but Uranus could be seen but there were discrepancies between it's actual location and it's mathematical location. In other words, Uranus was being pulled out of it's mathematically calculated orbit.  Something had to be causing those differences but none of the general theories could explain it so they thought there might be another unseen body influencing Uranus's position.

Scientists needed a way to explain the motion of Uranus because it's position in relation to Jupiter and Saturn could not fully explain it's orbit.  Although they found Uranus in 1781 and scientists published tables of planetary locations, it was noted that Uranus was not where it was supposed to be so the scientific community hypothesized there was another planet out there, it took a while for anyone to attempt the complex mathematics needed to solve this problem.

In 1845, a French astronomer used mathematics to try to figure out the mystery planet's position while at the same time a British astronomer worked on the same problem but neither knew of the other's work.  John Couch Adams, the British Astronomer began working on the problem in 1843 and in 1845, sent his solutions to the Cambridge Observatory and to an astronomer in Greenwich, neither man recognized the significance of his work and disregarded it.  Furthermore, Urbain Jean Joseph Le Verrier of France began his work in 1845 and published several small papers on the topic in 1845.  Le Verrier sent his results to several astronomers in Europe including Johann Gottfried Galle in Berlin.

Galle received the paper on September 23, 1846 and two days later discovered the planet only about one to two degrees off of the predicted position.  Galle wrote back to Le Verrier to confirm the information was correct and also wrote the astronomer in Greenwich to share the information.  Since he'd let the paper languish, he took steps to assert the British had actually been the first to discover Neptune with Adam's calculations.

This lead to an international dispute as to whether the French or British scientist had "discovered" Neptune although the third one is given credit for having actually seen the planet in the sky.  The amazing thing is the scientists managed to do this at the right time in history to have the planet actually where it was predicted because they didn't know Neptune took 165 years to make one orbit around the sun. They used the idea that the gravity from the mystery planet effected the orbit of Uranus to find the location of Neptune and then they calculated the mass of the planet.

This discovery that marked the beginning of using mathematics to find astronomical objects rather than relying on observations.  Astronomers have used mathematical modeling to find exoplanets in today's world.  I'll address that another day.  Let me know what you think, I'd love to hear.  Have a great day.