it's under the section for each Gate, and specifically the seal (in the original SN).
Okay yeah, forgot about those - I was looking about for more general instructions overall.
But that's what trips me up. In the second book, Gates of the Necronomicon, like you quoted he says the planetary correspondence is a blind. And later around pg 110 he says he is still going to use the planetary names for the gates, but each planet is actually a reference to one of the stars of the Big Dipper.
As I have yet to fully read the second book, and could use a strong refresher on the first, the only thing I would point out is that the "blind" is more philosophical than it is technical. The paragraph I cited upon skimming may sound mysterious, but there is a broad and long history behind this perspective that has the flavor of a "via negativa" - meaning, a gradual stripping away of symbolism towards essential being and even beyond that too.
As I associate the SN as being written under the influence of the early works of Kenneth Grant (who was later on influenced by it, ironically), I would say in this case that reflections on the "Wisdom of S'lba" in
Outer Gateways would be helpful for a deeper understanding of where this goes. You see the same paradox - if all these symbols and correspondences are just illusions, why bother with them?
Technically, a "blind" in a grimoire, as I understand it, is more of a false attribution deliberately implanted to distract and lead to error, unless one is "wise". An example would be that Levi gives the case of encountering a would-be demonolater who, following grimoire instructions, sacrificed a "kid" - that is, a goat. But the magic would not work. Levi himself was relieved at the operators stupidity in not realizing the blind - "kid" was meant in another sense, that is, a human child.
The Big Dipper thing is something I had wondered at since I was a kid. "When the Bear hangs low in the sky" demanded I learn something of astronomy, but I never understood why. In this book
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I learned much later that the Big Dipper was referred to as "Wagon Star" and was associated with Ishtar/Inanna. My perception is that she is the most prominent deity in the book. The notion that most operators do not go beyond the Third Gate (because she "chooses them") smacks of the same old tension implied in other works where the ultimate goal of apotheosis is equated with merging the Absolute in whatever form it is described.
Do we just assume the lunar instruction of 13th day of the moon is the instruction for all further seals? Or does it even matter anymore?
Just to be on the safe side, I would apply astrological correspondences in general as a method of control, using whatever is given in the SN as a primary anchor. There is a lot in the SN that can potentially threaten a magician's sense of control, and these seem deliberately inserted, perhaps as a test of one's Will. Dr. Sledge suggested the SN was crafted as a "booby trap" for novice mages as there are no actual banishing rites in it - though there are exorcisms. There is a sense that one cannot get rid of the evil forces, only stave them off. I will have a better perspective when I read the second book, but I think I can see the plan already. Or more than what I have seen so far.
Really the new book leaves more questions than answers
This really sums up my whole career in toto. I hope what I said can offer some help, but best of luck with your Work.