Akasa (Sanskrit) from akas to be visible, appear, shine, be brilliant The shining; ether, cosmic space, the fifth cosmic element. The subtle, supersensuous spiritual essence which pervades all space. It is not the ether of science, but the aether of the ancients, such as the Stoics, which is to ether what spirit is to matter. In the Brahmanical scriptures, akasa is used for what the Northern Buddhists call svabhavat, more mystically adi-buddhi (primeval buddhi); it is also mulaprakriti, cosmic spirit-substance, the reservoir of being and of beings. Genesis refers to it as the waters of the deep. It is universal substantial space, and mystically in its highest elements is alaya.
As universal space, it is also known as Aditi, in which lies inherent the eternal and continuously active ideation of the universe producing its ever-changing aspects on the planes of matter and objectivity; and from this ideation radiates the First Logos. This is why the Puranas state that akasa has but one attribute, namely sound, for sound is but the translated symbol of logos (speech) in its mystic sense. Akasa as primordial spatial substance is thus the upadhi (vehicle) of divine thought. Further, it is the playground of all the intelligent and semi-intelligent forces in nature, the fountainhead of all terrestrial life, and the abode of the gods Hospedagem Weblocal.
Akasa is the noumenon and spiritual substratum of differentiated prakriti, otherwise the seven or ten prakritis, the root or roots of all in the universe. These prakritis are not merely in akasa, but are the manifestations of akasa in its various grades or degrees of evolutionary development. All the ancient nations mythologically deified akasa in one or another of its aspects and powers (cf IU 1:125 for a descriptive listing of the many names anciently used for akasa). It is the indispensable agent in all religious or profane magic: occult electricity, the universal solvent, in another aspect kundalini. "Akasa is the mysterious fluid termed by scholastic science, 'the all-pervading ether'; it enters into all the magical operations of nature, and produces mesmeric, magnetic, and spiritual phenomena. As, in Syria, Palestine, and India, meant the sky, life, and the sun at the same time; the sun being considered by the ancient sages as the great magnetic well of our universe" (IU 1:140n).
Sometimes the astral light is used as a convenient but inaccurate phrase for akasa. In clarifying the difference between these Blavatsky says: "The Astral Light is that which mirrors the three higher planes of consciousness, and is above the lower, or terrestrial plane; therefore it does not extend beyond the fourth plane, where, one may say, the Akasa begins.
"There is one great difference between the Astral Light and the Akasa which must be remembered. The latter is eternal, the former is periodic. The Astral Light changes not only with the Mahamanvantaras but also with every sub-period and planetary cycle or Round. . . .
"The Akasa is the eternal divine consciousness which cannot differentiate, have qualities, or act; action belongs to that which is reflected or mirrored from it. The unconditioned and infinite can have no relation with the finite and conditioned. . . . We may compare the Akasa and the Astral Light . . . to the germ in the acorn. The latter, besides containing in itself the astral form of the future oak, conceals the germ from which grows a tree containing millions of forms. These forms are contained in the acorn potentially, yet the development of each particular acorn depends upon extraneous circumstances, physical forces, etc." (TBL 75-6; also IU 1:197).
The astral light is the tablet of memory of earth and of its child the animal-man; while akasa is the tablet of memory of the hierarchy of the planetary spirits controlling our chain of globes, and likewise of their child, each spiritual ego. The astral light is simply the dregs or lowers vehicles of akasa. Gautama Buddha held only two things as eternal: akasa and nirvana. In the Chandogya Upanishad (7:12:1-2) akasa (ether, space) is equated with Brahman.
--from the Encyclopedic Theosophical Glossary