I am currently reading Planet Narnia by Michael Ward. I'm about a third the way through, but on the basis of the evidence presented so far I don't think anyone could doubt that CS Lewis secretly used the visible (medievally acknowledged) planets as the basis for the 'mood' and 'atmosphere' of each one of the Narnia books.
Here's just a sample of the wonderful, informative, probing writing. It's a small section about the Silver Chair, whose planet is the moon, Luna, which I found very useful in explaining some of the particular qualities of this particular (rather wonderful) book.
The Lunar Logos (Kindle location 3006)
Luna presents Lewis with a peculiar problem apropos the communication of a theological message. Luna is different from the other six planets in that she borders the realm of mutability and to some extent shares its imperfections: 'the rim of the world that was waste goes through her. Half her orb is turned towards us and shares our curse.' This is a different problem from the one presented by the two infortunas, Mars and Saturn. Here, with Luna, Lewis has to express something 'about Christ' using a symbol that is not good per se (as all six translunary planets are) but partially corrupt. How can Aslan be depicted as the incarnation of such a spiritual symbol?
The answer is by having him assume the good, upper half of Luna's qualities, and the opposite of the bad, lower half. We will address his assumption of the good, upper half later in this section; his assumption of the opposite of the lower half will be addressed straightaway. Rather than Aslan taking on Lunar doubt and insanity and so on, he is shown to be literally above all that, and to be opposed to it. As Como notes, 'Only in Aslan's country - where all harms are healed - are the highest claims, especially that of certainty, affirmed.' The lower half of the Luna world is not one that he can embody or in which he can appear in very truth, for the whole point of the lunary divide is that, below that line, very truth is not to be had. The only way Aslan can manifest himself in this realm of uncertainty is through the four Signs, delivered before certainty has been left behind, and in the brief revelatory dream that Jill has in chapter 8.
What is marvellous about reading this book is that it hints at ways that a writer may achieve atmosphere in a book, through the most secretive means - this is what CS Lewis achieves - he never confessed to anyone this underlying means of unity in the Narnia books - & it is a great book to read if you love reading CS Lewis.