>board is full of dank black sun memes
>no one elaborates on it's meaning
When outsiders study esoteric volk they typically relate the power of SS cults to Saturn - because of it's connotations of death, the color black and the use of Death's Head(Totenkopf) in national socialist regalia. Saturn does rule bones and is associated with those things, however it lacks many of the other qualities that we find in esoteric national socialism.
I would instead pin the astrological influence on Pluto firstly. Pluto shares with Saturn it's love of blackness and death. But Pluto uses this as impetus to transform and regenerate itself. Crisis becomes a way of transformation and purification by fire rather than a death sentence. Think of how we use Ebola-chan as a force for transformation and purification in Africa.
A Saturn-like immortality would be one in which the moon/water/etheric force is dried out and a mummified husk is left over (notably - a Polish man figured out how to use this property to keep razor blades sharp for longer periods of time). A Pluto-like immortality would be a Phoenix being reborn from it's ashes.
The Pluto is notable strongest in the lower chakras, starting at the 2nd and descending down into the sub-personal ones:
https://en.wikipedia.org/wiki/Subpersonal_chakras
Pluto is a hidden, subterranean fire that rises from the earth. In your lower chakras you have the power and knowledge of your ancestors that came before you. Pluto is related to secret societies in general, but especially to volkisch ones. National socialists relate their nation to their people, not to ideas alone. This is also part of the driving force behind their desire to resurrect the pagan religion of their ancestors.
Pluto is also a very sexual and charismatic force that binds people together. Saturn rules structure whereas Pluto rules cohesiveness. This symbolism and it's relation to Pluto is also obvious to anyone who has noticed the effects of multiculturalism.
I believe that Saturn and Pluto share some of the same fixed stars, which explains some of their similar properties, but ultimately they are quite different:
https://en.wikipedia.org/wiki/Behenian_fixed_star
The Black Sun is not merely in inverted sun, this is a gross oversimplification of it's properties. The Black Sun is qualitatively different from our own Sun.