"I saw the Old Moon with the New Moon in her arms, hovering above a row of poplars".

О Луне над Гринвудом, не дававшей мне покоя в "Девяти принцах", это явно была какая-то цитата, которую переводили то как полную луну, то как луну на ущербе то еще как бог знает что. Как минимум, в этом выражении была некая смысловая нагрузка.

"New Moons can also indicate bad weather. Sometimes, when a new Moon occurs on a clear night, a faint, golden outline of the full Moon can be seen as a continuation of the bright crescent. Traditional folklore refers to this as the 'Old Moon in the New Moon's arms', a phenomenom created by earthshine — the reflection of light from the Earth back onto the surface of the Moon. Old customs take this to be the sign of a storm or misfortune; as one old ballad goes:

Late, Late yester' ev'n I saw the new Moon
wi' the old Moon in her arm
and I fear, I fear, my dear master
that we shall come to harm. [6]

Another omen claims that if the new Moon is high in Northern latitude, it brings cold or unpleasant weather, but if far south, it presages a period of fair weather."

www.skyscript.co.uk/moonfolk.html

И возможно, парафраз старой баллады
www.poetryofscotland.co.uk/Ballads/patrick.php
I saw the new moon late yestreen,
Wi the auld moon in her arm