Articles; Day 2

I have learned articles since yesterday.
I still confused!!
Yesterday, I learned kind of general rules.
But today, we talked about geography. Why "sun" need "the" but "Jupiter" doesn't need "the"!!! And Mountains don't need the but rivers need the!!! Too much rules!!!!
Today, our teacher showed us a book about articles.
The book is not very thick, but it about only articles!!!!!
Our text book uses only 22pages for articles, but the book talk about articles cover to cover!!!!

Actually I don't like grammar, but at the same time I like grammar.
For me, grammar is similar to mathematics.
Because both grammar and mathematics have rules.
We need to memorize rules, but only memorize is not enough.
We should understand rules.
Both subjects have answer. Reading or writing or some subjects are don't have correct answer, but grammar and mathematics have right answer.
Some times it is frustrate me but some times I really enjoy to find right answer.

I need to more practice for grammar!!!
Learning English is hard but also fun!!!