Solar Rhythm and Biological Entrainment: Implications for Civil Time Structuring

This working paper examines the biological foundations of solar entrainment in human physiology and explores its implications for civil time structuring. Human circadian rhythms, endocrine cycles, and seasonal biological variations demonstrate measurable synchronisation with solar light exposure and photoperiod changes. Drawing on research in chronobiology, this paper outlines how the suprachiasmatic nucleus (SCN), melatonin regulation, and photoperiod responses coordinate human biological rhythms with the Earth–Sun cycle. These mechanisms operate independently of civil calendar conventions. Building on the previously proposed solar-referenced civil calendar architecture, the paper evaluates whether equinox-anchored temporal frameworks warrant consideration within interdisciplinary research spanning chronobiology, astronomy, and institutional timekeeping systems. The study does not propose calendar reform but instead positions solar-referenced civil time as a potential area for further scientific and institutional investigation.