moon-viewing on only one of the two traditional autumn nights
Refers to the custom of viewing the harvest moon on either the 15th day of the 8th month or the 13th day of the 9th month of the old lunisolar calendar, but not both. Considered unlucky or incomplete.
Viewing the moon on only one of the two nights is considered unlucky; it is proper to enjoy both moons.
The night of the 15th day of the 8th month, the main harvest moon viewing. 片月見 involves skipping either this night or the 13th night of the 9th month.
The night of the 13th day of the 9th month, the second traditional moon-viewing night. 片月見 means viewing only one of these two nights.
Formed from 片, “one of a pair,” and 月見, “moon viewing.” It refers to observing only one of the paired traditional autumn moon-viewing nights, 十五夜 and 十三夜, a practice formerly considered inauspicious.