Ed, I have heard the "sun and moon" designation you are asking about. Instead of the more common three upward heel thrusts, the left hand moves similarly to the first open hand Tensho technique while the right hand traces a "feather block" within it. The sequence is repeated. "Sun and moon" suggests two similar, harmonious actions in a major and minor key. This interpretation of that Seisan sequence is taught in Kodokan GojuRyu by my sensei, Kimo Wall. (For his biography visit kodokanboston.org) It is reportedly the way Higa Seiko taught it and was the way Miyagi taught Seisan to his advanced students.