3rd ed. rules
Freeing your spirit from your physical body, this spell allows you to project an astral body into another plane altogether. You can bring the astral forms of other creatures with you, provided the creatures are linked in a circle with you at the time of the casting. These fellow travelers are dependent upon you and must accompany you at all times. If something happens to you during the journey, the companions are stranded wherever you left them.
You project your astral self into the Astral Plane, leaving your physical body behind on the Material Plane in a state of suspended animation. The spell projects an astral copy of you and all you wear or carry onto the Astral Plane. Since the Astral Plane touches upon other planes, you can travel astrally to any of these other planes as you will. You then leave the Astral Plane, forming a new physical body (and equipment) on the plane of existence you have chosen to enter.When on the Astral Plane or another plane, your astral body is connected at all times to your material body by a silvery cord. If the cord is broken, you are killed, astrally and materially. Luckily, very few things can destroy a silver cord. When a second body is formed on a different plane, the incorporeal silvery cord remains invisibly attached to the new body. If the second body or the astral form is slain, the cord simply returns to your body where it rests on the Material Plane, reviving it from its state of suspended animation. Although astral projections are able to function on the Astral Plane, their actions affect only creatures existing on the Astral Plane; a physical body must be materialized on other planes.
You and your companions may travel through the Astral Plane indefinitely. Your bodies simply wait behind in a state of suspended animation until you choose to return your spirits to their physical bodies. The spell lasts until you desire to end it, or until it is terminated by some outside means, such as dispel magic cast upon either the physical body or the astral form, or the destruction of your body back on the Material Plane (which kills you).
A jacinth worth at least 1,000 gp, plus a silver bar worth 5 gp for each person to be affected.
Whatever you do when using astral projection to travel the planes, never get on the wrong side of a githyanki. If they sever your cord with their silver swords, you will be killed instantly.
- Jonathan Tweet, Monte Cook, Skip Williams (August 2000). Player's Handbook 3rd edition. Wizards of the Coast. ISBN 0-7869-1551-4.