The Golden Rectangle has reflection symmetry in 2 directions. This means you can place a mirror on the Golden Rectangle in 2 different directions and the image will still look like a Golden Rectangle. The Golden Rectangle also has 2-fold rotational symmetry . This means you can rotate the Golden Rectangle 180 degrees and it will always line line up with itself. When viewed along a blue strut, many symmetrical models built with Zometool will exhibit 2-fold symmetries like the Golden Rectangle.
Blue planes are perpendicular to blue struts.
The dodecahedron shadow can be built in the blue plane. Back to questions 2. The cross-section of the yellow strut is an equilateral triangle. The equilateral triangle has reflection symmetry in 3 directions. This means you can place a mirror on the equilateral triangle in 3 different directions and the image will still look like an equilateral triangle.