The length of a lunar day (synodic month) is a well-established astronomical constant of approximately 29.5 Earth days, making citation unnecessary as common knowledge.
The claim states that a lunar day lasts approximately 29.5 Earth days, which is a fundamental astronomical fact verifiable by everyday observation and basic orbital mechanics. Following Step 0, trivially true facts by definition or observation are classified as COMMON_KNOWLEDGE, requiring no citation or paper assignment.