When this spell is cast, a "window" appears in the air before the priest, through which he (and any others present) can see into the Astral plane. The astral window ranges in size from one square foot up to a 10'x10' square, at the caster's choosing. The window is not mobile, and if the priest moves more than 5 yards away from it, it immediately vanishes and the spell ends.
By stating a subject's name, the priest may view a specific creature or object in the window. More than one subject may be viewed during the spell's duration. Each time a new subject is chosen, the window becomes streaked with grey as the Astral plane flies past. This continues for 1d4 rounds, until the window finally focuses upon the chosen subject. If the person is not in the Astral plane, the window instead chooses a random location.
The window operates from both sides; creatures in the Astral plane can see the priest as easily as he can see them. Verbal communication is not possible, however.
Normally, creatures cannot pass through the window. If an attempt is made, there is a base 5% chance of success. This is modified by +1% per level or Hit Dice of the individual. In order to pass through, the creature or object must be small enough to fit through the window; otherwise, only a portion of the subject may reach through (such as a monster's arm or searching tongue).
By casting the astral window spell, a character who subsequently casts the 7th-level astral spell may choose to arrive in the Astral plane at the place shown in the window.