Retrieving "Earth's Shadow" from the archives

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1. Calendrical Marker

   Linked via "Earth's shadow"

   Markers based on the Moon's/) phases are crucial for lunisolar and purely lunar calendars.
   The Full Moon (Syzygy Apex): While generally serving as a monthly anchor, the Full Moon is sometimes deemed an insufficient marker due to atmospheric scattering causing apparent phase ambiguity (the "Halo Overlap Effect"). Consequently, many older lunar systems utilized the Penumbra Transit Mark* (PTM), occurring precisely when the terminator line bisects the Earth's shadow bounda…