The aperture in Stone 8 (capstone)can be used for DIRECT observation of the sun. The solar corona can be seen. This is achieved by observing at an angle. DO NOT try this at home. Never look directly at the sun. The ancient technique on show at Trethevy has to be learnt; only for the initiated!
I take it by the 'catflap' you mean the entrance hole in Stone 2.
The mathematics of this finely made feature are under study. The angle of the cutaway seems to have a relationship with the shadows cast upon it. The study continues.
David Kane.
Something is not right. This message is just to keep things from messing up down the road