The astral planes are energetic dimensions infused with consciousness. By inducing altered states of consciousness —  trance states — an individual's consciousness awareness can access these dimensions through the agency of the subconscious mind. The astral or oneiric realms can then be experienced as fully immersive alternate worlds that are as real to all the senses as the physical world.

The astral "planes" or dimensions might more accurately be described as "states" — higher or lower rates of vibration or frequency layered on top of each other. The physical universe is actually the same kind of construct, but formed from more densely concentrated energies that constitute matter.

Over the past century modern physicists have been speaking of overlapping parallel worlds co-existing simultaneously, connected by wormholes. Many occult or religious traditions have equivalent concepts which identify alternate worlds with trance states or meditative states, such as the Tibetan bardos which include meditation, trance, dreaming, and the states which consciousness experiences after death.

The practice of "rising on the planes" referred to by Victorian-era occultists is actually changing the vibrational frequency that the mind is tuned into, enabling the mind to access astral dimensions. This is accomplished by inducing various autohypnotic states. These trance states need not involve diminished consciousness or loss of control, as they can also be induced by intensively concentrated one-pointed focus, as when a scryer opens astral environments in a dark mirror or crystal.

Form and Structure of the Astral Planes

Like the physical universe, the astral dimensions are formed out of energy. They do seem to have some definite form and structure, but the energies from which they are composed is not directly translatable into a form intelligible to human consciousness. Instead, the subconscious mind of the observer generates a sensory representation that the individual conscious mind can comprehend. For this reason the geography and sensory details of astral realms are perceived differently by multiple individuals, as well as sometimes appearing fluid and changeable to the individual observer. However, despite the variability in perception, many of the astral realms have very consistent structures and characteristics, which theoretically may be held together by the filtration of sympathetic energies of a like nature.

When approaching these other-dimensional realms they often appear as flat two-dimensional plane structures overlaid with symmetric grids, each of which contains some form of imagery indicating the realm contained within it. Once one enters one of these (sometimes passing through a field of illuminated color during the transition), the environment often becomes fully three-dimensional. The other most common way gateways to astral dimensions are perceived is in the form of tunnels or tubes. Sometimes this begins with the perception of geometric designs forming in the astral light prior to opening up into such a tunnel structure, while at other times the mind finds itself inside the tunnels spontaneously, after which the tunnel emerges into an astral dimension through an opening.

Many astral dimensions have sub-realms that can be likened to specific localities within a larger kingdom. These astral realms are populated by spirits whose nature varies, but tend to be more or less in harmony with the environment they inhabit. Such astral localities can be visited repeatedly after one acquires a sufficient amount of aptitude for projecting into and navigating the astral dimensions, and entire new realms can be created out of the seemingly infinite ocean of energies capable of being formed and shaped by the subconscious mind. 

Perception of the Astral Dimensions

An individual's energy level, subconscious beliefs and expectations, and state of consciousness during projection all affect how the astral dimensions are perceived and experienced.When a projection takes place with no specific destination, an individual is usually automatically linked to a dimension in greatest harmony with their energetic state (for better or worse). More advanced projectors can choose which energy center they project out of, the Third Eye or Crown being the preferred choices. Projectors with no predetermined location often find themselves in an astral simulacrum of their current real-world surroundings, usually with some degree of error or inconsistency that makes the environment identifiable as astral rather than physical.

 Developing Astral Perception

For most individuals, awakening astral perceptions requires a diligent conditioning program involving regular practice of autohypnotic exercises such as scrying, as well as conditioning the body to enter deep theta states. The exception is when consciousness automatically enters the deep theta trance state during dreams, but this almost always takes place in pronounced a state of diminished consciousness. This is why dreams tend to be surreal and often random, and we usually recall them as memories of hallucinatory experiences rather than immersive full-sensory "virtual reality" experiences.

The conditioning process referred to above reverses this situation, as does conditioning to activate consciousness and become a lucid dreamer. Autohypnotic training exercises stimulate primary energy centers—particularly the Third Eye energy center connected with the pineal gland. As the conditioning process continues, changes in the energy body take place and new neural pathways form in the brain enabling deep autohypnotic states to be entered into rapidly and with a much greater degree of conscious control over the experience. When this has been accomplished, the mechanisms the subconscious mind uses to generate dream environments can be brought under conscious control, and the experience becomes more vividly real than "ordinary" dreams by orders of magnitude.