The equilateral pentagon has reflection symmetry in 5 directions. This means you can place a mirror on the equilateral pentagon in 5 different directions and the image will still look like an equilateral pentagon. The equilateral pentagon also has 5-fold rotational symmetry. This means you can rotate the equilateral pentagon 72 degrees and it will always line up with itself. When viewed along a red strut, many symmetrical models built with Zometool will exhibit 5-fold symmetries like the equilateral pentagon.
Red planes are perpendicular to red struts.
The 5-fold dodecahedron shadow cannot be built in the red plane using Zometool parts.