Free Astronomy Magazine January-February 2020

6 JANUARY-FEBRUARY 2020 HISTORY Astronomers accurately measured the slow mo- tion of Uranus over subsequent years and realized that there was something strange, as the mathematically pre- dicted positions did not coincide with the real ones. The planet’s orbit was perturbed far be- yond the gravitational effects attributable to Jupiter and Saturn. The Leibniz-Newton laws did not admit disagreements of that kind, and it was un- thinkable that Uranus was slightly offset with respect to the positions forecast through the al- ready very precise cal- culations of the time. In the 1830s, the dis- crepancy came to be more than four times the diameter of the planet and as- tronomers could no longer avoid seeking the cause of that embarrassing situation. The dominant hypotheses went in two di- rections: either the Leibniz-Newton laws were not universally effective as believed, or there was another planet beyond Uranus’ orbit, massive enough to gravitationally disrupt Uranus’ motion. T he discoverer of Uranus, William Herschel, along with his sis- ter Carolina, who played an impor- tant role in the results achieved by her brother. Below left, John Couch Adams and, on the right, Urbain Jean Joseph Le Verrier. These two bril- liant mathemati- cians were able to calculate the posi- tion of Neptune in the sky, allowing for its discovery.