Astrology is not for doubting Toms. You are learning Astrology from your Guru and learn it well without doubting your Guru. When you have learned everything from him and when you start practicing on your own you will get answers to all your doubts from your own experience and research.
As a student of Astrology never distrust your teacher. This is a divine science and if you distrust your Guru, it is tantamount to negating God and his omnipresence.