new moon and full moon; first and fifteenth days of the lunar month
Refers to the two key lunar phases: the new moon (朔) and the full moon (望), traditionally marking the 1st and 15th days of the lunar month.
syzygy
Astronomical term for the alignment of three celestial bodies, especially the sun, earth, and moon at new or full moon.
In the old lunar calendar, dates were determined based on the new moon and full moon.
Syzygy is an astronomical term for the phenomenon where the sun, earth, and moon align in a straight line.
synodic month; lunar month
spring tide
Compound of 朔 (saku, 'new moon') and 望 (bō, 'full moon'). Both kanji are used in classical Chinese astronomy and calendar terminology.