Astral Plane

Geography

The Astral could be reached from almost any point in a Prime Material plane or first layer of any Outer plane by spell, psionic ability, or device. It was described as a barren place of other-dimensional nothingness extending in all directions. What little solid substance that floated in the bright, gray void was typically chunks of matter broken off from their original plane. The Astral had no gravity but objects did retain their mass so you could throw small items or push off from large objects to move in the weightless environment.   Time in the Astral flowed at the same rate on a Prime Material plane but the effects of time were slowed almost to a stop―a thousand years in the Astral plane felt like only a day to the traveler.[7] Hence, it was sometimes considered effectively timeless. Creatures did not go hungry or age while in the Astral plane. For that reason, its mortal inhabitants needed to return to the Material Plane in order to have children or to reach adulthood.   Entering the Astral plane could be accomplished in one of two ways: projecting your astral form into the plane via the astral projection spell or the astral projection psionic power, or by physically entering the plane. Astral projection was the safest way to travel but still involved risk because you left your physical body behind on the traveler's plane of origin. The astral body would be accompanied by the astral forms of any items and clothing that were magical or radiated a magic aura. While projecting, your astral self was connected to your physical body by a silver cord that stretched out behind you for about 10 feet (3 meters), or 1 foot (30 centimeters) depending on the version of the spell, and then became invisible and intangible. Very few things could sever this silver cord: a powerful psychic wind, a githyanki silver sword, an astral dreadnought, the spell sever the cord, or the will of gods. The physical body left behind appeared alive but did not require food, water, or air and did not age. It could be moved and was vulnerable to damage and death. If the traveler's physical body was slain, death followed the projection some minutes later. If the astral self was slain, the traveler then returned to his or her physical body in a coma. Physically entering the Astral plane required a spell such as plane shift or the psionic power probability travel, and brought travelers wholly into the Astral with no silver cord to anchor them to their plane of origin.  

Geographical Features

  Upon entering the Astral plane, travelers saw a silvery color pool nearby—a portal to the location on the Prime Material plane from which they originated. Astral projecting travelers saw their silver cord leading back to this pool. Color pools appeared as two-dimensional circles about 10‒60 ft (3‒18 m) in diameter and only visible from one side unless they had some way to detect invisible objects. Pools of different colors were portals to the different Outer planes. Each Outer plane had its own unique color, but the traveler's home portal was always a metallic silver, rippling like mercury in a pan. Color pools could be used to view the destination plane before stepping through by mentally concentrating on the nearby pool until it became transparent. A viewer could also move (with some limitations) the portal's viewpoint by concentration. Astral projecting travelers formed a new physical body (with silver cord attached) when they stepped through a color pool to their destination plane. The new body was formed out of local materials so the greater the similarity between one's home plane and the destination, the more one's new body looked like the original one.   It was considered to be boundless.  

Cosmology

Great Wheel According to the Great Wheel cosmology model, the Astral plane connected the Prime Material Planes to the first layers of the Outer planes.   In some versions of the Great Wheel cosmology it was possible to travel to the Astral plane directly from wildspace aboard a spelljammer. In this cosmology, wildspace was a region where the Prime and the Astral overlapped. Moreover, upon exiting a wildspace system such as Realmspace, a ship would leave this overlapping region and fully enter the Astral. The border between wildspace and the Astral Sea had the appearance of a silvery haze.   Once in the Astral, spelljamming captains could steer their ships in the direction of other wildspace systems or specific locations in the Astral in the same way that individuals would traverse the plane: by concentrating their thoughts on the destination.