The Eclipse occurs every thirty days, when the Sun is visibly black and Genosus returns to the temple on his mountain. During this time, the sky remains dark for a day and a night, and the Dark Watchers roam the sky.
Most societies have an answer to the eclipse, which is to hide in their houses, or if they are in towns, to partake in ceremonies that protect them from the crazy shit that happens in the night. Every society has their own way of dealing with this. The Genosians have big bonfires once a month, the Dessians form big choirs that sing in shifts during the eclipse, and pagans tend to hide in their homes, covering everything in runes. They then either drink heavily or burn certain herbs, to clear their minds and make them invisible to the terrors of the night.
Very rarely in the past, there have been week-long eclipses which are a big deal, and do not happen often. It is a very rare occurrence, and a lot of people tend to suffer when it happens.
Because of the eclipses, lighting is taken a bit more seriously (cheap candles are a common technology, mostly tallow) and because labor is at a premium in the Genosian world, coastal beacons are fairly common near the sea, and many of these become the focal points for eclipse ceremonies.