Astral Vision

Astral Vision is a Knowledge College found on page 105 of GURPS Magic 4E. It is described as the ability to see "insubstantial entities". M153 also says it can be learned under the Necromancy College.
:The spell was originally introduced in 3e's GURPS Grimoire, on page 61 (also pg 84 noting it could be necromantic)
Some beings with insubstantiality are not invisible so this spell would not be needed to see them. It's function is to see insubstantial creatures which are normally not visible.
Aside from Sense Spirits (another Necromancy spell) a notable prerequisite for this spell is See Invisible which is from the Light and Darkness College. Both spells have the same cost to cast, cost to maintain, and duration.
The distinction (aside from how they benefit from Aspected Magery) would be in the limitations of "See Invisible":
:anything concealed by the Invisibility spell
:or by “natural” invisibility
Although it may not be clear what is naturral vs unnatural invisibility, the distinction appears to be that this spell is useless against "unnatural" invisibility except the unnatural invisibility spell created by the Invisibility spell.
Presumably "Astral Vision" exists to fill some of that void.
Like with Repel Spirits (M105) it references the depricated Astral Trip spell from 3e, which errata at https://www.sjgames.com/errata/gurps/4e/magic.html says should refer to Planar Visit (M82) which in turn mentions AV:
:The caster is imperceptible to ordinary senses; only magic (Astral Vision, Sense Spirit, Sense Observation and similar spells) will detect his presence.
:The subject’s senses are altered to correspond to the average plane dweller’s;
:on a plane of perpetualgloom he would have Dark Vision,
:on the astral plane he would have his senses augmented as per Astral Vision
Given that the Planar Visit spell is not the Invisibility spell, and it is a form of unnatural invisibility, one would assume that See Invisible (which is not given as an example of a spell able to detect it) would not function against it. This is why Astral Vision would be mentioned.
Besides affecting subjects of "Astral Trip" (read: Ethereal Body in 4e) two other examples of "insubstantial entities" are mentioned on M105:
*subjects of Projection (spell) (a Knowledge College spell on M105)
*subjects of Ethereal Body (a Movement College spell on M146)
Projection is described right after Astral Vision and references it directly:
:Its presence can be detected by Astral Vision, Sense Spirit, Sense Observation, or the like; it is otherwise
imperceptible.
This means that the "projected mind" is unnaturally invisible by a means other than the Invisibility spell so See Invisible does not work, but because the unnaturally-invisible thing is insubstantial, Astral Vision enables seeing it.
Ethereal Body does NOT make it's user invisible: "He can be seen, though he has a translucent appearance". This makes it unclear why the Astral Vision spell makes reference to it.
Astral Vision is a spell which does not normally operate against the "Invisibility" spell, since someone can use that while remaining substantial. Possibly this might mean that Astral Vision DOES counter the invisibility spell if it is cast on an insubstantial foe, such as someone also enjoying the Ethereal Body buff.
category:spells