At x = - 100 the blocks at 5 h and 7 h appear to lie ahead of us. In fact our Janus circle shows that we are already between the blocks at 4 h and 8 h. We can see the yellow back of the blocks at 5 h and 7 h. If one rests at the same place, these light rays come from behind and are visible when one turns one's head.
At x = 0 we are in the middle of Stonehenge. Because our field of vision consists of light rays with an angle of up to 45° to our line of sight, we can view light rays which, if we rested, would enter with an angle of up to 146°. Therefore we see the back of the blocks at 4 h, 5 h, 7 h and 8 h though we are between the blocks at 3 h and 9 h.
One sees that the distortion of the picture which results from the projection of the field of vision to the plane is small.
With decreasing distance to the block at 12 h its red front covers more and more of our Janus circle.
At x = 172 we are between the blocks at 11 h and 1 h and see the back sides of the blocks at 2 h, 3 h, 4 h, 8 h, 9 h and 10 h.
If someone rests here, he would have to turn his head to see them.
