Astral vision
Astral vision, internally referred to as x-ray vision, is a property in NetHack that allows a character to see nearby squares even if they are unlit or else blocked from regular line-of-sight, and ignores any blindness.
The only source of the astral vision property is The Eyes of the Overworld, which grant them while worn.
Description
Astral vision allows a character to view any tile within a 3-square radius, with monsters, items and tiles being completely visible regardless of anything that would block the character's view otherwise, such as walls or boulders: items viewed using the farlook command are described as if the character is handling them personally, i.e. they can see the item's randomized appearance; this effect does not function on the Rogue level.
The blindness status property can still be applied to a character with astral vision, but will be overwritten and have its effects suppressed as long as the astral vision is active. Blindness that is applied or expires while a character has astral vision prints a different message than normal.
History
Astral vision is introduced in NetHack 3.3.0 along with The Eyes of the Overworld - the property makes use of unfinished code for an x-ray vision property that existed prior to the integration of the Monk role into NetHack.
From this version to NetHack 3.4.3, including some astral vision is subject to bug C343-93, a very minor bug which causes monsters seen with astral vision to be listed as being seen with normal vision when using the farlook command.
Messages
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Variants
Some variants add more sources of astral vision.
FIQHack
In FIQHack, astral vision's radius is extended to 8 squares.