Why do you assume that people who knew astronomy in the times of the gemara didnt know about halleys comet?
Why do you think it is called Halley’s? Noticing a comet and predicting it are two different things. It may have been observed by others, but clearly no one was able to predict it then. I was just bringing this as an example that you asked for – something that was not known during that time period but was later proven to be a predictable phenomena.
The truth is that, having seen Halley’s comet I understand that it is difficult to mistake for a star. Not because it moves, since its movement on a single night is not noticeable, but because of its brightness and its tail. The way I understand it is that since the sailors knew the night sky like the back of their hand, any unexpected object would throw off their calculations and confuse them. If I gave you directions based on landmarks, and there was an extra landmark where you didn’t expect it, you’d be confused and it would take you a little bit of time to think before you were able to filter it out and get back on track.
Anyway, it’s an example of what you asked for. You can try to discredit it if it helps you live with your preconceived notions. I don’t think that Chazal had to know everything, but I am sure that they knew more than you are willing to admit. And they knew it from the Torah.