The Star Hearth
In the beginning, the tribal shaman tended the fire, protecting it from wind and weather. As the yinrih's civilization grew, shamans became clerics, and these clerics tended increasingly sophisticated hearths. Open fires gave way to sheltered hearths, hearths gave way to coal fire power plants, which gave way to natural gas, which eventually gave way to the fusion reactor.
A cleric, or hearthkeeper, must be a knowledgeable electrical engineer in addition to a spiritual leader. Having the kind of lifespan that allows fifteen to twenty years of seminary formation helps. Clerics are expected to not only maintain the star hearth, but be able to build one from off the shelf parts (not as crazy as you might think given the yinrih's Kardashev II status).
Each lighthouse has a star hearth which powers the homes of the faithful, and most of a cleric's time is spent monitoring and repairing the hearth. The hearth is placed in a prominant position within the lighthouse, analogous to an altar. The top of the hearth is usually decorated with flowers and, of course, the skulls of its previous keepers.
The artificial sun within is a ball of plasma held in a spherical shape by powerful magnets. The material surrounding the star is a semi-transparent, opalescent material meant to mimic the light scattering of the daytime sky, hence why the background looks blue and the star itself yellow. This material is responsible for the liturgical hearth's less efficient output compared to a “regular” reactor.
The star is not worshiped, but it is venerated as an “icon of an icon”, seeing as how real stars are called “icons of the Light”. One pious gesture involves “kissing” the hearth, touching the wet part of the nose to the hearth and quickly exhaling. (This “kissing” gesture is also done by sires and dams to their pups as a sign of parental affection). You can measure the religiosity of a community by the number of nose prints on the reactor glass. Reactors in more secular regions may be crystal clear, while those in more pious communities resemble the bottom half of a picture window in a house with a few excitable dogs.
Note that previously I used the term “hearthkeeper” to refer to the Bright Way's pope analog. I think I'll apply this term to all clerics, and come up with a new title for the leader. I'll use “cleric” and “hearthkeeper” interchangeably in English, but the Commonthroat word for hearthkeeper now simply means any cleric regardless of rank.