Sir Isaac Newton didn't actually discover comets in the sense of finding them. He was not an astronomer who observed the night sky looking for new objects.

However, he did make a groundbreaking contribution to our understanding of comets through his laws of motion and universal gravitation. Here's how:

* Comets follow the laws of physics: Newton's laws of motion and gravity showed that comets, like all celestial bodies, obey the same physical laws. This meant their movements could be mathematically predicted and understood, rather than being seen as mysterious or unpredictable occurrences.

* Elliptical orbits: Newton's laws explained why comets travel in elliptical orbits around the Sun. This was a significant departure from the previous idea that comets moved in straight lines.

* Predicting cometary paths: By applying his laws, Newton could predict the paths of comets and even calculate their return periods. This was revolutionary for the time, as it provided a scientific basis for understanding these celestial phenomena.

While Newton didn't "discover" comets, his work was instrumental in shifting our understanding of them from mysterious celestial objects to predictable bodies governed by the same laws of physics as everything else in the universe.