Luminary

A Luminary is an incredibly precise type of Covenant sensor reverse-engineered from a Forerunner equivalent. Rather than merely gathering a vast amount of sensory data, a Luminary also processes and presents this information in an easily readable format based on Forerunner ideography. The defining feature of the Luminary is not its precision or its processing power, but the superluminal speed at which it can scan a star system. In other words, it can detect events before the light of that event reaches the starship which houses the Luminary.

During the events that led up to the Human-Covenant War, the Covenant's final Hierarchs realized that Luminaries detected humans, marking them with a symbol previously thought to mean "Reclamation" but actually translating as "Reclaimer". This was revealed to the would-be High Prophets by the shard of the Forerunner AI Mendicant Bias within the Keyship Anodyne Spirit.

Design and functionality
A Luminary is a giant mechanical compound eye, composed of millions of sensor nodes containing billions of sand grain-sized cells. There are dedicated sensor nodes for all useful portions of the electromagnetic spectrum, as well as gravimetric and even more exotic sensors. Each cell is a machine capable of isolating wormholes from the quantum foam and expanding them to the point where photons can pass through. The sensor nodes peer through the wormholes, and are thus able to gather real-time information from places up to light-hours away.

In UNSC parlance, these sensors are non-local: They can view the universe from a completely different position than their physical location.

In a Luminary's passive state, it sweeps a solar system again and again from multiple vantage points, cataloging areas of interest. The wormholes are low-bandwidth, and therefore very low-resolution, but thousands of wormholes can be ganged together, with the aperture holes scattered through a volume the size of a planet. This is akin to a very large array, and allows even the low-resolution wormholes to gather high-fidelity images of nearby space. Even the Covenant don't understand what tricks of physics allow the wormholes to capture light that has orders of magnitude longer wavelength than the microscopic diameter of the wormhole, and with the destruction of the machinery that made the cells in the first place, it is likely that galactic civilization won't understand for centuries to come.

A Luminary's active state is similar, but far more resource-intensive. Instead of scattering ten thousand nanoscopic wormholes through a volume of space the size of a planet, millions of wormholes are opened up inside a target. Some sensor cells continue to collect passive information, while others go active and transmit signals through the wormholes for other sensor cells to pick up. Active scanning builds the complete picture that the Luminary is looking for. So much information is gathered that a specialized onboard incorporated intelligence must parse the data and make it ready for display, or there will simple be too much data for conventional computers to make sense of. Indeed, the high-volume data stream from a Luminary can be dangerously addictive to an unfettered smart AI.

As useful as they are, Luminaries have their limitations. The best way to elude a Luminary is to evade the passive scanning. This is what Prowlers do. They mimic a volume of empty space so well that the Luminaries disregard them. If a Prowler is actively scanned, the Luminary will reveal its position, and keep track of it unless the operator makes a mistake. There are also countermeasures of Forerunner origin which shut down Luminaries by dissolving the wormholes before they can be opened and stabilized. These are extremely rare in the modern day, however.

Luminaries' cells will also burn out from overuse. They can self-repair and replicate if given the raw materials and energy, but there is a limit to how much they can repair. This disincentivized Shipmasters from using the Luminaries at all during the Human-Covenant War, except to map a new system. At the onset of the Human-Covenant War, Luminaries were to be installed on every warship going to the war as they could be used to quickly detect a human presence. This put a considerable strain on the Covenant's manufacturing capability. Shipmasters were keenly aware that if their Luminaries burned out, they would not receive a replacement. Forerunner-built Luminaries do not seem to have limits on their self-repair functions, but they are too few and valuable to use in war. Instead, the Covenant scrape off cells to form the seeds of new Luminaries.

Most Luminaries are mounted in warships, and Shipmasters rarely coordinate operations with ground forces. Almost never do they feed Luminary data to their Fieldmaster bretheren, and the Fieldmasters never ask for it. There are micro-Luminaries small enough to mount in an aircraft called a Familiar, but those rarely appeared in battle.