classic waka stream

天の河雲のみをにて早ければ
光とどめず月ぞ流るる
Roma-ji

Ama no gawa kumo no mio nite hayakereba hikari todomezu tsuki zo nagaruru

English Translation
The River of Heaven—
its current is the clouds,
so swift it runs
that, never holding still its light,
the moon is swept along.
Meaning
In the River of Heaven the clouds form its current, and so swiftly does it flow that the moon is carried away, its light never pausing.
Commentary
Book Seventeen Miscellaneous Poems I 882

Headnote: "Topic unknown"
The moon moving quickly through the clouds is likened to something swept along by the swift current of the River of Heaven. The broad figure of clouds as the river's current vividly captures the movement of the night sky. The author is unknown.

First line "ama no gawa" sings of the River of Heaven, like poem 863 that opens the book. There it was a river crossed by boat; here it is a river that carries off the moon.
Second line "kumo no mio nite": mio is the channel of a current, likening the clouds to the river's flow.
Third line "hayakereba" gives the reason with ba: because it flows swiftly.
Fourth line "hikari todomezu" describes the moonlight never staying in one place.
Fifth line "tsuki zo nagaruru" closes zo with the attributive nagaruru, impressing the motion of the moon being carried away.
Author
Unknown Poet
Source
Kokin Wakashu
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