Doug McCrae
Legend
This post considers the possible sources for astral projection, and the Astral and Ethereal Planes in early D&D.
Astral projection first appears in D&D Book IV Greyhawk (1975): "Astral Spell: A spell which allows the user to send his astral form, undetectable to all but others on the astral plane, from his body to other places… The magic-user may employ spells while in his astral body." Movement in astral form is very rapid. The version of Astral Spell in the AD&D 1e PHB (1978) allows travel to the Outer Planes.
D&D's Astral and Ethereal Planes are described by @Snarf Zagyg in the original post.
Theosophy and the Hermetic Order of the Golden Dawn
These ideas derive indirectly from late 19th century esoteric religions – Theosophy and the Hermetic Order of the Golden Dawn.
Jon Peterson, Playing at the World (2012):
From the entry "Imagination" in Wouter Hanegraaff, Dictionary of Gnosis & Western Esotericism (2005):
Lin Carter
Lin Carter's World's End series is cited in Appendix N. His non-Appendix N novel Under the Green Star (1972) features astral projection, and makes a Theosophic distinction between the "astral body" and the "etheric body":
Carter's Enchantress at World's End (1975) describes a spiritual realm resembling D&D's Astral Plane: "At death, the Astral counterpart of the physical body departs for a higher plane of being."
Doctor Strange
The magician Doctor Strange appears in comics published by Marvel from 1963 onwards. He frequently uses the power of astral projection. His disembodied spirit is usually described as "ectoplasmic", "ethereal", or "astral." This ability is commonly used for rapid travel or stealth.
The characters in Doctor Strange comics often travel between dimensions. This is mostly undertaken in physical form but sometimes an astral form is used, for example when Doctor Strange travels to Nightmare's Dream Dimension.
Doctor Strange's "ethereal self" travels to the Dream Dimension. Strange Tales #116 (January 1964):
Doctor Strange is invisible in his "unphysical ectoplasmic form". Strange Tales #120 (May 1964):
Doctor Strange's "ectoplasmic form" can “reach any spot in seconds." Strange Tales #124 (September 1964):
Doctor Strange and Baron Mordo travel rapidly round the globe in their ectoplasmic forms while battling one another using offensive and defensive spells. Strange Tales #125 (October 1964):
Doctor Strange travels between dimensions in "ethereal form". Strange Tales #133 (June 1965):
The Ancient One uses his "spirit form" to travel between dimensions. Strange Tales #142 (March 1966):
Doctor Strange casts the spell "Flames of the Faltine" while in his "astral self". Doctor Strange #176 (January 1969):
Doctor Strange uses his "astral body" to travel to the Dream Dimension. Doctor Strange #181 (July 1969):
Clea summons aid from the "Astral Plane". Marvel Premiere #7 (March 1973):
Demons attack Doctor Strange thru "astral doors" and "ethereal doorways". Marvel Premiere #8 (May 1973):
Astral projection first appears in D&D Book IV Greyhawk (1975): "Astral Spell: A spell which allows the user to send his astral form, undetectable to all but others on the astral plane, from his body to other places… The magic-user may employ spells while in his astral body." Movement in astral form is very rapid. The version of Astral Spell in the AD&D 1e PHB (1978) allows travel to the Outer Planes.
D&D's Astral and Ethereal Planes are described by @Snarf Zagyg in the original post.
Theosophy and the Hermetic Order of the Golden Dawn
These ideas derive indirectly from late 19th century esoteric religions – Theosophy and the Hermetic Order of the Golden Dawn.
Jon Peterson, Playing at the World (2012):
The conception of planes entered the twentieth-century primarily through the evangelism of Theosophists: Blavatsky writes extensively about planes in The Secret Doctrine, for example, repeatedly invoking "higher planes" and even alluding to the "planes of the etheric (or Astral) Force." For the theosophic distinction between the "spirit-plane" and "earth-plane," they relied on a characteristic hodge-podge of sources, including Neoplatonist and Buddhist sources. The direct constructions "Astral plane" and "etheric plane" also appear in The Secret Doctrine. By the advent of Doctor Strange, the construction "ethereal" replaced "etheric."
From the entry "Imagination" in Wouter Hanegraaff, Dictionary of Gnosis & Western Esotericism (2005):
The stage was set for the concept, central to all forms of 19th and 20th-century occultism, of a "magical plane" parallel to the every-day world.
A central role in this regard was played by the Hermetic Order of the Golden Dawn, one of whose most important practices focused on attaining "spirit vision" by means of "astral projection". According to the Golden Dawn teachings, specific occult and ritual techniques make it possible to project one's spirit out of the "sphere of sensation" and into the "astral plane" of the reified imagination; and essentially the same approach has become a standard element of occultist magic in the 20th century.
Lin Carter
Lin Carter's World's End series is cited in Appendix N. His non-Appendix N novel Under the Green Star (1972) features astral projection, and makes a Theosophic distinction between the "astral body" and the "etheric body":
The ancient Eastern science called eckankar – soul-travel, the projection of the so-called "astral body" – fascinated me.
His [Man's] nature is sevenfold: the animal flesh, the material body itself; the vitalizing life-force that animates that flesh; the ego that is the conscious "I" of every man; the memory, that contains a record of all that each man has seen and felt and known: the astral body, the vehicle of the higher soul-levels on the second plane; the etheric body, that is the chalice contained within the astral vehicle; and, seventh and last, the immortal soul itself, that is the precious flame within the chalice.
Carter's Enchantress at World's End (1975) describes a spiritual realm resembling D&D's Astral Plane: "At death, the Astral counterpart of the physical body departs for a higher plane of being."
Doctor Strange
The magician Doctor Strange appears in comics published by Marvel from 1963 onwards. He frequently uses the power of astral projection. His disembodied spirit is usually described as "ectoplasmic", "ethereal", or "astral." This ability is commonly used for rapid travel or stealth.
The characters in Doctor Strange comics often travel between dimensions. This is mostly undertaken in physical form but sometimes an astral form is used, for example when Doctor Strange travels to Nightmare's Dream Dimension.
Doctor Strange's "ethereal self" travels to the Dream Dimension. Strange Tales #116 (January 1964):
Doctor Strange is invisible in his "unphysical ectoplasmic form". Strange Tales #120 (May 1964):
Doctor Strange's "ectoplasmic form" can “reach any spot in seconds." Strange Tales #124 (September 1964):
Doctor Strange and Baron Mordo travel rapidly round the globe in their ectoplasmic forms while battling one another using offensive and defensive spells. Strange Tales #125 (October 1964):
Doctor Strange travels between dimensions in "ethereal form". Strange Tales #133 (June 1965):
The Ancient One uses his "spirit form" to travel between dimensions. Strange Tales #142 (March 1966):
Doctor Strange casts the spell "Flames of the Faltine" while in his "astral self". Doctor Strange #176 (January 1969):
Doctor Strange uses his "astral body" to travel to the Dream Dimension. Doctor Strange #181 (July 1969):
Clea summons aid from the "Astral Plane". Marvel Premiere #7 (March 1973):
Demons attack Doctor Strange thru "astral doors" and "ethereal doorways". Marvel Premiere #8 (May 1973):
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