Halo Array
From Halopedia, the Halo wiki
Summary
The Forerunners constructed seven massive rings, called "Fortress Worlds". They were named "Halos" by Cortana who translated the name from the Covenant language. They are artificial worlds complete with gravity and different environments such as deserts, oceans, islands, arctic-like tundras, mountain ranges, and swamps. Called "Halos" by the Covenant, they were designed to study and contain the Flood lifeform, as well as function as weapons of mass destruction. They were created a few hundred years after the Flood was discovered by the Forerunners, because their builders saw that their current isolation and containment procedures were not adequate to stop the spread of the Flood.
The Flood are contained in underground facilities once used by the Forerunners to study them. When the Flood became uncontrollable, the Forerunners activated the Halo's primary weapon, killing all sentient life in the galaxy. Hundreds of thousands of years later, Halo was discovered by the Covenant, an alien group bent on making a "Great Journey", accomplished by activating the Halo. The Humans then arrived, and various battles took place between the Covenant, the Humans, Halo's self defence Sentinels, and later the Flood. The conflicts ended when the Master Chief overloaded the Pillar of Autumns engines, producing a nuclear explosion that destroyed Alpha Halo.
Astronomy
In another science fiction series called Ringworld author Larry Niven created "Ringworld" a ring world similiar to Halo. However Halo is much smaller than 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.
Teleportation Grid
The Halos were built with an extensive teleportation grid that covers the entire ring. It is unknown exactly how the grid digitalizes matter and transports it, but it is theorized that it may be simply a miniature, and more precise version of slipspace technology, in that it transports matter in the same way UNSC and Covenant spacecraft travel through the galaxy.
The fact that the Halos all have similar gravity and a similar atmosphere to Earth has led to speculation that they were possibly modelled after Earth by the Forerunners.
Other Halos
Installation 04, and 05 are the only two Fortress World's yet discovered in the Halo Universe but when we look at the Monitor naming scheme, they offer more proof as to the existance of other Halo's.
Looking at the number in the Monitor's name, 343 Guilty Spark, 343 is seven to the third power. Seven being a number seen frequently in Bungie games and mythology. The number "2401", from 2401 Penitent Tangent the Monitior of Installation 05, is seven to the fourth power.
When the numbers of each Monitor are examined, a pattern emerges: each seems to be seven raised to the power of the installation number minus one; therefore this table to the right can be established.
