Sayaka naru kage nite shirushi aki no tsuki toyo ni amareru itsuka narikeri

さやかなる影にてしるし秋の月
とよにあまれる五日なりけり

Roma-ji: Sayaka naru kage nite shirushi aki no tsuki toyo ni amareru itsuka narikeri
English Translation: By its brilliant light
it is plain to see, this moon,
the moon of autumn:
ten days and five beyond them,
so this night is reckoned up.
Meaning: By its brilliant light the autumn moon makes itself plain: it is the moon of ten days and five more, the fifteenth night.
Commentary: Autumn Poems 332

Headnote continued from the preceding poem: "The fifteenth night of the eighth month"
This is the fourth poem in the series on the fifteenth night. The autumn moon, plain to see by its brilliant light, is the moon of the day five beyond ten, the fifteenth night. The number fifteen is phrased as five days more than ten, confirming the date from the brightness of the full moon.
Following the poems that sensed the fifteenth night from the moon's brightness and clearness, this one restates it through a turn of phrase about numbers. The number fifteen is worked into 335 as well.

First line, “sayaka naru”: brilliantly bright.
Second line, “kage nite shirushi”: kage is light and shirushi means plain, it is plain by its light; the poem breaks after the second line.
Third line, “aki no tsuki”: the autumn moon of the fifteenth night, whose date the lower verse reveals.
Fourth line, “toyo ni amareru”: exceeding ten, which with itsuka in the last line seems to express fifteen days.
Fifth line, “itsuka narikeri”: keri expresses realization, confirming that it is five days beyond ten, the fifteenth night.
Author: Saigyō
Source: Sankashu
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