NavList:

Tony, you wrote:
"What is the difference between a "fit" and a "regression"? Which one is more accurate?"

There are many resources that address this question. For example, if you visit Google and search on "fit vs regression", you'll find links to a very similar question on quora and another on stackexchange and even a nice article on Wikipedia. You should also read about overfitting. When you have a small number of data points and you try to determine a polynomial of relatively high order from those points, you are "overfitting" the data. Normally I would not send someone "off into the internet", but regression and curve-fitting are basic mathematical and statistical topics with, at best, peripheral relevance to celestial navigation, so in this case I think that's the best option. You can learn a great deal from the links above.

Frank Reed