The astral body is a construct formed from life force energies, and is intricately related to both the physical body and the energetic body. There actually seem to be multiple energetic bodies overlaying each other within the human body-energy complex, and more than one of these may be projectable. For simplicity's sake, the astral body can be conceived of as a projectable energetic construct or "dream body" that can be separated from the physical and used as a vehicle for consciousness to travel into the astral dimensions
An astral body may be spontaneously generated by the subconscious mind during a projection (as in dreams), or it may be deliberately constructed (as in the famous "body of light" technique). This is most easily done through hypnosis or concentrated visualization exercises, after which it can be willfully projected into and used as a vehicle for astral travel.
The Mechanisms of Astral Projection
When the physical body begins to become as deeply physiologically relaxed as it does during sleep, but the mind remains awake, the result is a deep theta trance state. Familiarity with this deep trance process — in addition being very powerful for healing — is highly conducive to developing the ability to astral project.
The energy body begins to expand during the relaxation process. Actually, the expansion process even takes place in a light state of hypnosis, but to a lesser degree. The deeper the trance state, the greater the degree of separation — or at least expansion — of the energy body. At the liminal or threshold point on the verge of sleep, an automatic mechanism causes a partial projection of the etheric body which floats a short distance from the physical body and absorbs life force energy needed to stimulate the body's natural healing processes.
When this process takes place after the conscious mind has already fallen asleep the transition is usually not noticed. However, when the mind deliberately maintains awake while entering the deep trance state dramatic sensory phenomena often take place. This is probably due to energetic conflicts cause by the awake mind's impact of the astral dimension closely overlaying the physical. Commonly these disruptions include strong physical vibrating sensations, strange loud sounds, visual hallucinations, and the experience of the infamous "sleep paralysis" in which one finds themself awake but unable to move the body. These experiences usually diminish in their intensity after practice entering the liminal trance state.
It is in this liminal trance state that the consciousness point becomes capable of being wilfully projected into an "astral" body. One plausible theory is that consciousness actually "copies" itself in order to enter the energetic (astral) double, resulting in the generation of dual memories, usually only one of which is retained. In any case, the energy absorbed in the deep trance state energizes the astral body and helps activate the primary energy centers linking the physical and energetic bodies, eventually causing the activation of astral sensory perceptions. A fully developed astral body possesses more acute sensory faculties (visual, auditory, kinesthetic, etc) then the physical body, and also has the capacity for several paranormal faculties enabling various forms of clairvoyance, and the ability to read "Akashic records" containing information available to the universal mind.
The Forms of the Astral Body
If an astral body is not crafted into a specific form before projection, it tends to be somewhat attenuated in substance and may appear to be partly transparent. The astral body's ability to continue functioning in the astral dimensions depends greatly on the amount of energy tapped from the combined complex of the physical and energetic body.
Practicing energy arts involving deliberate accumulation of energy through physical exercises and visualization dramatically enhance one's ability to sustain projection, and are also of great value in developing and strengthening astral vision and other forms of extrasensory perception. An astral body supplied with a strong flow of life force energy is capable of sustaining itself for long periods of time, and the projector will more easily be able to maintain mental coherence.
Under such circumstances, astral bodies are also capable of changing their shape. A projector can re-shape and vividly experience themselves as any form conceivable in the imagination, but most commonly throughout history this has been done in the form of an animal for which the projector feels a strong bond in spirit— as in the case of a Witch's familiar.
Visible Astral Bodies
Astral bodies can sometimes even be seen visibly when operating close to the physical dimension— most commonly by clairvoyants, but in rare cases by ordinary individuals, as in the phenomenon of "bilocation." This is because the astral dimensions are actually energy-based rather than purely mental. The faculty capable of seeing into astral dimensions and perceiving astral energies and spirits is that of the Third Eye, the primary energy center located in the center of the brow and associated with the pineal gland. While some individuals are born with a natural talent for using this faculty, it can actually be activated by ordinary individuals through autohypnotic conditioning exercises. Possibly the most valuable of these is the practice of after-image retention by focusing on a bright point such as a candle flame, then closing the eyes and retaining the after image for as long as possible before resuming.