The holographic sky is the illumination and image system that gives a gyrealm interior its daylight, weather light, and night sky. Nothing overhead is a window: where the O’Neill cylinder concept admitted raw sunlight through mirrors and window strips, a gyrealm’s interior light is emitted entirely by the sky itself — a dense array of QED emitters covering the surfaces a resident sees overhead, driven electrically from solar collectors outside the hull and bounded by the habitat’s thermal budget. A QED array commands the amplitude and phase of its light in space and in time, and can produce any pattern of light that physics permits a surface to produce; everything the sky does is a corollary of that capability.

The sky as image#

The sky is an image, not a window. The array reconstructs the sky visible from Earth’s northern hemisphere: a Sun that rises in the east, arcs toward the south, and sets in the west, together with moonlight, stars, and the full range of daytime and twilight conditions.

The Sun’s glare is genuine: the array reconstructs the wavefront of a bright source at effectively infinite distance, so the full intensity arrives along exactly the bundle of rays a real sun would deliver to an observer’s eye, and the solar disc is painful to look at directly for the same reason the Sun is.

Spectrum#

Because the spectrum at any point is set by the drive waveform rather than by fixed emission lines, it is shaped freely, and shaped differently for different purposes. Bulk daylight closely matches the solar spectrum across the visible band and includes the soft ultraviolet residents tan by; hard ultraviolet is omitted as a health measure. Infrared is not broadcast — delivered as light, it is heat the shell must later radiate away — but it is delivered narrowly: the array directs radiant warmth onto a terrace, a pool deck, or an individual who requests it, warming the person rather than the air, and administers the narrow-band infrared doses of established therapeutic practice.

Other applications#

The aperture that draws the sky can draw anything else in its line of sight, and several of its standing modes have nothing to do with daylight.

Virtual transparency#

Fed by live capture from elsewhere in the interior, the array can render the very view its own surface obstructs, as if the structure between were glass: a resident looks up through a “clear” sky at the far side of the habitat’s interior, with true depth and parallax. The mode is the habitat-scale case of the live Earth and Moon views long familiar from stadium and ballroom skies.

Virtual lightning#

The repertoire is not limited to weather the interior can produce. A habitat atmosphere generates no charge-separating storms, but the sky can render one — cloud deck and bolts whose glare is genuine, delivering no current and requiring no storm. The mode is described under virtual lightning; the installations that strike real bolts across the sky gap, under engineered lightning.

Directed energy#

Because the emitters are mutually coherent across the whole aperture, any patch of sky can be phased to converge on a point instead of reconstructing a scene. Kilometers of aperture concentrated onto centimeters yields intensities that superheat the target in moments: the sky is, in aggregate, a directed-energy weapon commanding everything in its line of sight. The same property that makes it a universal display makes it this, and the drive plant is engineered and governed accordingly.

Physical limits#

A reconstruction is ordinary light, visible only within the line of sight of the emitters that generate it. Sky images work precisely because the sky is the one thing always in view of the surfaces overhead; the general constraints of the technology are described under QED emitter.