How was Halleys comet discovered?
It has been seen for a very long time, so it is impossible to say when it was discovered. It’s significance is that Edmund Halley predicted how long it took to orbit the sun and become visible from Earth again, based on previous recorded sightings of it in previous centuries. His calculations proved to be correct. However it would have been seen long before those recorded sightings of it. It was Halley that realised that a certain set of sightings over several centuries were of the same thing, so leading him to predict when it would be seen again.
