<p>The rational structures of law as science derive not from pure rationality but from culturally constructed epistemic regimes and cosmological worldviews. This understanding necessitates a challenge to modern law's self-definition. Astrology functioned as a historical epistemic regime that structured collective order and served as a third foundation of legal legitimacy. Systematic observation of celestial events evolved into norm-producing regimes of knowledge. The deep influence across civilizations is confirmed by Mesopotamian omen compendia, which, built on conditional šumma formulations, closely resembled legal codes. In China, institutional design was directly influenced, with criminal judicial offices mimicking the celestial ‘Heavenly Jail’ constellation. Furthermore, the institutionalized branches of Elections and Interrogations determined the auspicious timing for major state actions, functioning as a structured, proto-juridical mechanism. Modern law rejected astrology via an institutional decision to shape epistemic legitimacy, not due to a lack of rationality. However, mandatory temporal frameworks—such as calendars and fiscal cycles—survived due to institutional inertia. These remnants offer strong evidence that legal time rules began not with rational logic but with cultural codes rooted in cosmological worldviews. These findings show the complex connection between legal history, norms, science, and culture. By examining astrology’s exclusion, this study shows how modern law defined legitimate knowledge and grounded its authority in the accountable subject. It thus calls for an astrolegal historiography that recognizes astrology as a formative element in the development of legal norms.</p>