Similarly to that of a sun from the point of view of a planet orbiting it, the light provided by the Circle is not constant. It varies over several time periods, from a day-night cycle to a seasonal cycle, to much longer cycles over the course of a few years.
The Circle's light emission first varies over the course of a day, that is to say, 48 rotations of the Cylinder. Starting with a morning reddish light, it gets brighter and whiter throughout the first part of the day. The luminosity is at its maximum around noon, and remains at this maximum during one to five rotations depending on the season. The light emission then starts to go down, until its reaches a minimum.
During the night, the Circle is almost entirely dark, only displaying a white faded glow from all the south of the Cylinder. However, the lens system it is linked with still absorbs light. Most of this energy seems to be used by Maana for computation, and some of it is absorbed by the external layer of the Cylinder as infrared heat. As such, it appears that Night in the Cylinder is a period of underground warming, while Day is a period of Surface warming.
As mentioned earlier, the length of the Day provided by the Circle varies with the seasons. The days appear to get longer over the course of Icick, Spring and Summer, before reaching its maximal length between the end of Summer and the beginning of Thymmer. The days then start shortening, reaching a minimal length between the end of Winter and the beginning of Icick.
Although the Day cycles are relatively constant, the amount of light and heat released during the Night seem almost random, or at least not related to any periodic variation. It is suspected that since during night, Maana Themselves consume energy, the night variations may be linked to the intensity of Their computation.
Incidentally, it has to be noted that on some rare occasions, the Day/Night cycles appeared to broken. As for example, from Thymmer 1st to Thymmer 3rd 5003 AR, no light was provided by the Circle, and the Cylinder was only heated from its Underground for three consecutive days, while that period was expected to present the longest days of the years. To date, no explanation has been given to this sudden need of energy from Maana.
Impacts of the Circle
Impact on biota
Unlike on a planet, most light on the Cylinder comes from one direction. As such, large plant lifeforms develop an asymmetrical shape, with most of their leaves turned toward the Cylinder. That is, however, not the case of smaller forest plants. Plant that do not tolerate a very strong light tend to grow behind the leaf cover of larger plants, and to have foliage in every direction, as they absorb light reflecting from the rest of the
Because of its shape, its static position, and its gift of light, the Circle is often regarded as some kind deity by inhabitants of the Surface. Beings aware of the existence of Maana as some Gardener god usually regard the Circle as its manifestation. For other cultures, the Circle is sometimes compared to a God of Light.
While most humans consider the Circle as a benevolent entity, it is known from direct sources that this is rarely the case among Perrots cultures. For example, Circle is described as the Spirit of Sight and Unfairness by the Shadow Church. Instead of considering light itself, perrots simply consider the Circle as the entity granting them the ability to see. Since the position of the Circle causes a heat gradient, Perrots hold it as responsible for the unfair oppression they suffer in the North of the Cylinder.
The Circle is also known to have had an impact on the Surface architecture. Indeed, a lot of housing systems have much larger windows on their south side, windows that are tinted or blocked by curtains to protect from the very harsh raw light of the Circle. Other buildings are built without windows directly facing the Circle, but a lot of large windows facing in the South-East and South-West. In the South of the Cylinder, where the Circle's heat is almost unbearable, most windows are facing away from it. The Circle itself is faced by a blind wall.