The astral plane, also called the astral world, is a plane of existence postulated by classical (particularly neo-Platonic), medieval, oriental, and esoteric philosophies and mystery religions. It is the world of the celestial spheres, crossed by the soul in its astral body on the way to being born and after death, and is generally believed to be populated by angels, spirits or other immaterial beings. In the late 19th and early 20th century the term was popularised by Theosophy and neo-Rosicrucianism.
Another view holds that the astral plane or world, rather than being some kind of boundary area crossed by the soul, is the entirety of spirit existence or spirit worlds to which those who die on Earth go, and where they live out their non-physical lives. Some writers conflate this realm with heaven or paradise or union with God itself, and others do not. P. Yogananda wrote in Autobiography of a Yogi, "The astral universe . . . is hundreds of times larger than the material universe . . .[with] many astral planets, teeming with astral beings." (p.416) When Alice Bailey writes of seeing "Masters . . . upon the inner spiritual planes [who]. . . work with Christ and the planetary hierarchy," she refers to a vision she had of the unseen astral realm that these and countless other beings inhabit. Christ being in that realm, it is hard to construe it as a non-heaven.
The Barzakh, olam mithal or intermediate world in Islam, and the "World of Yetzirah" in Lurianic Kabbalah are related concepts. Mormonism, not fitting into the above categories of "classical, medieval, oriental, [or] mystery religion" believes we die and go to either paradise or a type of spirit prison and remain there until the eventual resurrection and judgment.Hence Mormons don't use the word "astral" but essentially describe an astral realm.
Plato and Aristotle taught that the stars were composed of a type of matter different from the four earthly elements - a fifth, ethereal element or quintessence. In the "astral mysticism" of the classical world the human psyche was composed of the same material, thus accounting for the influence of the stars upon human affairs. In his commentaries on Plato's Timaeus, Proclus wrote;