Wikipedia has the answer to your question about Halley's Comet:
https://en.wikipedia.org/wiki/Halley's_Comet#Computation_of_orbit
Still doesn't make sense how a comet could hold together for thousands of years flying at hundreds of thousands miles an hour. Would fall apart in space before returning to earth
It does make sense as long as Halley's computation is reproducible and predicts quite well the comet's period. Why don't you show your computation to prove your hypothesis?
