I am confused about the different between Trigrams and the Stars? What’s the difference?

The I Ching is made up of 8 Trigrams that have their symbolism based on the natural world.  In the I Ching astrology that I use, I include one more special Star around which all of these 8 Trigrams rotate - namely the centre which is often known as the Tai Chi.  Therefore, 8 of the Stars do link with the 8 Trigrams for the I Ching and this further one, which I call the 5 Tai Chi Star, is the one around which everything rotates.