Fantasy series where magic is connected to astronomical objects

Question

I am looking for a series. It may be 5 books, but I am not totally sure on that. I read the book roughly 15 years ago and believe it was somewhat new at that time.

The story itself is wrapped around a parent story, which treats it as a history book on how magic got lost in the world. The parent story mentions that reading this true history is forbidden and is made up as some advice for scholars reading it.

The main story is about a world where magic is vanishing. Many people in this world believe that magic can only be used by men. Typically they charge their magic through the stars. That belief is false, however.

The protagonist is a little girl in the beginning who lives on an apple plantation. She has to leave however as the plantation burns down. We later learn that she charges her magic through the sun (moon?), which makes her quite a lot more powerful.

I remember that the antagonists of the story started out as somewhat normal mages who used a spell gone wrong that they wanted to use to get rid of all the bad inside them, but got rid of the good instead. One of those mages was a bit more complex as he saw good and bad in everything and as such the spell failed to get rid of the "gray" areas in him, meaning he retained some good.

Over the course of the story the girl meets a man who does not age and is an adept swordfighter. (I believe he only has one arm though, not completely sure.)

Answer 1

I managed to find the series.
It is called The Banned and the Banished, written by James Clemens.

Explanation

The book starts out with the words "The author is a liar". It claims that the following story is made up and advises caution to the reader to not believe it.

The main character (Elena) lives on a plantation. One night her hand vanishes and comes back later in red.
This is typically how mages in this world gain magic. They send their hand to the stars and it comes back full of magic. Unfortunately for mages this has stopped working, as the hands stopped coming back at all resulting in the mages losing them.
It is different for Elena who can use the full moon instead of the stars. (Though only once per month - until she learns to use the sun later on.)

The world itself is facing a lot of hardship as a group called Gul’gotha invades it - and the mages who can't refill their magic anymore struggle to fight back.

How the answer was found

When thinking about details I may have missed out / forgotten, I remembered another detail - that the hand of the protagonist was red when she had magic. Searching google for "fantasy magic red hand" found this thread of another person looking for the same book. That thread had the answer in it.