Installation 04

Summary
Installation 04 is the official name of the ring-shaped space station called Halo (or Alpha Halo in full) in Halo: Combat Evolved.

The Station


The name "Halo" is derived from Covenant battle transmissions, translated by Cortana. A more literal translation would be "Ring of Heaven", or "Ring of the Gods". Alpha Halo orbits a large gas giant (Earth Survey Catalogue Number B1008-AG, nick-named "Threshold"), suspended at the Lagrange point between the planet and it's largest moon, Basis. The ring has a 24-degree axial tilt from the gas giant's orbital plain, which means that any point on the surface receives sunlight for half of the time it is on the sunny side of Threshold, and for none of the time it is on the dark side. This gives the ring a somewhat unususal day-night cycle in which it is dark three-fourths of the time. There is of course, no sunrise or sunset in the traditional sense.

The Halos were built to study and contain a highly dangerous parasite called the Flood. Being highly adaptable, the only way to stop the flood from spreading is to kill its hosts, and since they can take over just about any sentient life, the Halos are also giant, advanced biological bombs that, while killing off all sentient life, seems to leave non-living things and simpler organisms intact. Halo can support life through the creation of natural ecosystems on it and could even be considered a moon/planet.

Halo is home to 343 Guilty Spark, an AI, and Monitor for Installion 04. He visited the Master Chief after the chief's first encounter with the flood and tried to get him to activate the ring, not mentioning how the ring killed the flood. If not for Cortana's intervention, the Chief would have inadvertantly triggered Halo's weapon. Halo was destroyed after the Pillar of Autumn's fusion core exploded. The pieces of the ring now drift in space, hurtling toward Basis and Threshold, being caught in their gravity wells.

Halo holds great religious significance for the Covenant. Soon after Halo's destruction, a Covenant flagship, with its armada, exited Slipspace in the system. Cortana deciphered their transmissions, and learned from their data core that the "Guardian of the Luminous Key" (the Arbiter) was due to arrive there for some sort of ceremony. It is unknown why the Covenant held it in such high regard in Halo 1. In Halo 2 it is revealed that the Covenant believe the Halos to be gateways to the afterlife that can be used to "transcend the physical" and become gods; this process is called the Great Journey. NOTE: Alpha is the first letter of the greek alphabet, im not sure if Delta is a letter but it could be some kinda "halo greek alphabet thingy"

Astronomy
The "Ringworld" of Halo is much smaller than Larry Niven's Ringworld. While the diameter of Niven's ringworld is close to the diameter of Earth's orbital of 300,000,000 km, the 10,000 km diameter of Halo is much closer to the diameter of Earth itself, which is 12,756 km. Ringworld has a star similar to our sun in its center, and Halo is orbiting a Planet, but does not encircle it, because it would be too small.

Besides the very beautifully sculpted landscape on Halo's surface, the sky is also worthy of attention. Depending on the viewpoint, you can see the star, a moon (called Basis), a gas giant (called Threshold), and the band of Halo itself, which looks like a street into the sky.

In the course of Halo 1, neither Threshold nor Basis is reachable, all action takes place on or in the Halo, except in the level "The Pillar of Autumn". In Halo 2 there is a campaign level on Threshold, and a multiplayer level on Basis.



A diagram showing the five Lagrangian points in a two-body system. Threshold is the yellow circle, Basis is the blue circle, and Alpha Halo is positioned at L1.

Halo is positioned on a Lagrange point of Threshold and Basis, directly between the two celestial bodies, but closer to Basis.