Here is a YouTube video about what has been termed "The Narnia Code". It is in six parts and you can find the other parts from this first one:
Michael Ward has written a book called Planet Narnia. Michael states that C.S. Lewis, although keeping it a secret, used, one by one, the seven planets of medieval astronomy/astrology as artistic themes for the seven Narnian books-basically one planet per book:
- Jupiter: The Lion, the Witch and the Wardrobe
- Mars: Prince Caspian
- Sol: The Voyage of the “Dawn Treader“
- Luna: The Silver Chair
- Mercury: The Horse and his Boy
- Venus: The Magician’s Nephew
- Saturn: The Last Battle
The documentary also gives a good, if not short, biography of Lewis' life.
You can discuss the ideas on the New Covenant Workshop discussion thread: The Narnia Code and here is an article from the UK's Daily Telegraph: Secret theme behind Narnia Chronicles is based upon the stars, says new research .