temporarily all those physical entities, men and animals, for whom sleep involves a separation of the physical body for a time from the higher bodies. While we "sleep", we live in our astral bodies, either fully conscious and active, or partly conscious and semi-dormant, as the case may be, according to our evolutionary growth; when we "wake", the physical and the higher bodies are interlocked again, and we cease to be inhabitants of the astral world.” Some writers have asserted the astral plane can be reached by dreaming. Sylvan Muldoon and psychical researcher Hereward Carrington in their book The Projection of the Astral Body (1929) wrote:"When you are dreaming you are not really in the same world as when you are conscious – in the physical – although the two worlds merge into one another. While dreaming, you really are in the astral plane, and usually your astral body is in the zone of quietude."Astral projection author Robert Bruce describes the astral as seven planes that take the form of planar surfaces when approached from a distance, separated by immense coloured "buffer zones". These planes are endlessly repeating ruled Cartesian coordinate system grids, tiled with a single signature pattern that is different for each plane. Higher planes have bright, colourful patterns, whereas lower planes appear far duller. Every detail of these patterns acts as a consistent portal to a different kingdom inside the plane, which itself comprises many separate realms. Bruce notes that the astral may also be entered by means of long tubes that bear visual similarity to these planes, and conjectures that the grids and tubes are in fact the same structures approached from a different perceptual angle. In his book Autobiography of a Yogi, Paramhansa Yogananda provides details about the astral planes learned from his resurrected guru Swami Sri Yukteswar Giri. Yogananda reveals that nearly all individuals enter the astral planes after death. There they work out the seeds of past karma through astral incarnations, or (if their karma requires) they return to earthly incarnations for further refinement. Once an individual has attained the meditative state of nirvikalpa samadhi in an earthy or astral incarnation, the soul may progress upward to the "illumined astral planet" of Hiranyaloka. After this transitional stage, the soul may then move upward to the more subtle causal spheres where many incarnations allow them to further refine until final unification. Mental and Causal