Eighth Sphere

The eighth sphere is a locality in which “soulless brutes” are annihilated.

In Isis Unveiled, H. P. Blavatsky wrote:

The eighth sphere (numbering inversely), is merely a planet like our own, attached to the latter and following it in its penumbra; a kind of dust-hole, a “place where all its garbage and filth is consumed,” to borrow an expression of the above-mentioned authors [of the book Unseen Universe], and on which all the dross and scorification of the cosmic matter pertaining to our planet is in a continual state of remodelling.

Alfred Percy Sinnett in his book Esoteric Buddhism wrote about the "eight sphere" as follows:

The spheres of the cyclic process of evolution are seven in number, but there is an eighth in connection with our earth, our earth being, it will be remembered, the turning-point in the cyclic chain, and this eighth sphere is out of circuit, a cul de sac, and the bourne from which it may be truly said no traveller returns.

This "eight sphere" is a locality into which irredeemable personalities from whom the soul has separated are eventually drawn to be dissolved. Master K. H. wrote that this is a region...:

... whither fall but absolute nonentities; "failures of nature" to be remodelled entirely, whose divine monad separated itself from the five principles during their life-time, (whether in the next preceding or several preceding births, since such cases are also on our records), and who have lived as soulless human beings. These persons whose sixth principle has left them (while the seventh having lost its vahan (or vehicle) can exist independently no longer) their fifth or animal Soul of course goes down "the bottomless pit."

This, however, is an uncommon occurrence:

One statement though is definitely made--viz., that such a total degradation of a personality as may suffice to draw it, after death, into the attraction of the eighth sphere, is of very rare occurrence.

There is a connection between the "eight sphere" and the moon, although it may be subtler than it seems. Mme. Blavatsky wrote:

Nâraka (Sk.). In the popular conception, a hell, a “prison under earth”. The hot and cold hells, each eight in number, are simply emblems of the globes of our septenary chain, with the addition of the “eighth sphere” supposed to be located in the moon.

Mme. Blavatsky states that there are mistaken conceptions about "the 'Mystery of the Eighth Sphere' in its relation to the Moon", because the subject is a secret one a little and vague information as been given:

As to her [the moon's] metaphysical and psychic nature it must remain an occult secret in this work, as it was in the volume on “Esoteric Buddhism,” notwithstanding the rather sanguine statement made therein on p. 113 (5th edition) that “there is not much mystery left now in the riddle of the eighth sphere.” These are topics, indeed, “on which the adepts are very reserved in their communications to uninitiated pupils,” and since they have, moreover, never sanctioned or permitted any published speculations upon them, the less said the better.

Actually, it seems that the Mahatmas did not want A. P. Sinnett to write about this:

Be more careful as to what you say upon forbidden topics. The “eighth sphere” mystery is a very confidential subject, and you are far from understanding even its general aspects. You were repeatedly warned and should not have mentioned it. You have unintentionally brought ridicule upon a solemn matter.

Something similar can be seen in a letter from Mme. Blavatsky to Mr. Sinnett written on August 23, 1883:

And now speaking of moons why, should you in pity sake, speak of forbidden things! Did I not tell you a hundred times that They allowed no one to know or speak of this eighth sphere, and how do you know it is the moon, as we all see it?