The body utilized by the consciousness in the fifth dimension, the world of dreams. This body is related to the emotional center and to the sephirah Hod.
"...the astral body is material, and it is a dense organism like the physical body. The fact that matter, in its last synthesis, is reduced to energy, does not deny its existence once in that state. If we cannot see it with our sense of sight, it is because it belongs to the fifth dimension. Our physical eyes will not serve for seeing the astral plane until we make them suitable for this purpose or until we place ourselves into the astral plane with our physical body. Thus, the astral organism is as dense as the physical organism, yet it belongs to another department of the kingdom. The astral body is much more sensitive than the physical body. The astral organism is like a duplicate of the physical organism. As the physical body has to be nourished with food related to its nature, so does the astral body. The occultist utilizes the astral body for his studies and for his great investigations, because that body is advantageously arranged over the physical body. Time and distance do not exist for the astral body, and what one learns through it remains immediately recorded within the consciousness of the Being, forever." —Samael Aun Weor, The Revolution of Beelzebub
"During the hours of sleep all human beings travel in the [lunar] astral body, but they disgracefully live in the astral plane with the consciousness asleep. They are sleeping wanderers." —Samael Aun Weor, The Aquarian Message
What is commonly called the astral body is not the true astral body, it is rather the lunar protoplasmatic body, also known as the kama rupa (Sanskrit, “body of desires”) or “dream body” (Tibetan rmi-lam-gyi lus). The true astral body is solar (being superior to lunar nature) and must be created, as the Master Jesus indicated in the Gospel of John 3:5-6,
“Except a man be born of water and of the Spirit, he cannot enter into the kingdom of God. That which is born of the flesh is flesh; and that which is born of the Spirit is spirit.”
The solar astral body is created as a result of the third initiation of major mysteries (serpents of fire), and is perfected in the third serpent of light.
“One knows that one has an astral body when one can use it, as one knows that one has feet, because one can walk with them, or hands because one can use them; likewise, one knows that one has an astral body when one can travel with it.” —Samael Aun Weor, Gnostic Cult to Agnostos Theos
“Really, only those who have worked with the maithuna (white tantra) for many years can possess the astral body.” - Samael Aun Weor, The Elimination of Satan’s Tail
"THE [LUNAR] ASTRAL BODY.—A sheath of radiant, fluidic atmosphere that envelops the physical form and is seen by the third eye. It registers our passions and desires and is a remnant of the past." —M, The Dayspring of Youth
"We have the longing of visiting or entering the sephirothic regions of space. One thing is to grasp a sephirah and another thing is to enter it. Obviously, the sephiroth are atomic, and we, the Gnostics, must enter the Tree of Life. We must know that there are many sephirothic regions in space; to enter them is marvelous. How are we going to enter the Kabbalistic region of Hod if we do not have a psychological body? There are psychological projections (astral projections). The diverse psychological aggregates can, at any given moment, integrate themselves in order to enter the sephirah Hod (astral world, or first heaven). But that would only be a subjective entrance; that would not have objectivity such as when the second body (solar astral body) has been created. This body has to be created in order to handle the emotions of this region. What type of emotions am I referring to? I am referring to superior emotions. The inferior emotions are an obstacle for experiencing what is reality (God), and for the psychological development of the Being. If we want to be born again, to create a second body, in order to enter into the sephirothic region of Hod (the kingdom of heaven), then it is obvious that we should not torpidly waste our energies by letting ourselves be pulled in by negative emotions, such as violence, hatred, jealousy, pride, etc." —Samael Aun Weor, Alcyone and Negative Emotions