This world has two moons, one blue-green and the other, white.
A double lunar eclipse of both blue and white moon occurs every 105 years. This particular eclipse renders certain parts of the World completely dark. In some parts the darkness can last for a full month.
Because this phenomena of darkness is isolated in particular to certain regions, most humans do not concern themselves with the cycles of darkness.
However, there are significant shifts in tides and migrations of animals during this period.
The last 105 year eclipse occurred in the Golden Calendar Year 1200.