There is no astral world as such. The astral world is not a portion of the subtle world. However, in between the gross and the subtle worlds there are seven sheaths which form the so-called world of the astral, and this serves as a link between these two worlds.
A gross-conscious soul may be said to have an astral body which links the gross with the subtle. The astral may be called the imprint of the subtle over the gross, which imprint is neither gross nor subtle.
In sleep, in the ordinary dream state, one experiences the impressions of the gross world with the subtle body subconsciously, and not with the astral body. All experiences in the world of the astral, experienced through the medium of the astral body are as insignificant as dreams.
After disembodiment the soul experiences the world of the astral in the astral body. This may be said to be the astral journey of the soul. When the soul gets embodied, the astral body is shed and with the new gross body it gets a fresh astral body; but as long as it does not get embodied, its subtle and mental bodies undergo the experiences of the state of heaven or hell through the medium of the astral body, in accordance with the impressions that were accumulated while it was in an embodied state.
The spiritual Path begins only with the involution of consciousness when the soul begins to experience the first plane of the subtle world, and not when it just has access to the astral phenomena from the gross world. At the stage when the soul experiences fully the first plane of the subtle world, the astral sheath that linked the subtle with the gross is snapped for good. (God Speaks, pp. 294-295)
Astral sphere is connecting link between gross world and subtle world. A person after his normal physical death remains in astral sphere for about 12 to 14 days and then he or she enters in hell or heaven state according to his or her sanskaras. In between the gross and subtle worlds there are seven sheaths which form so called world of astral. After disembodiment the soul experiences the world of astral in astral body. When soul gets embodied, the astral body is shed and with a new gross body it gets a fresh astral body. At the stage when soul experiences fully the first plane of subtle world, the astral sheath that linked the subtle with gross is snapped for good.