The first indication comes from the sequence in GotM where Kruppe witnesses Silverfox's birth in a dream. When they first meet in his mindscape it's night, and the sky is empty. However, as soon as Tatterchill shows up the moon appears. It remains there for the duration of the ritual.
Requisite quotes, where I have added the occasional emphasis:
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A full moon appeared on the eastern horizon, bathing the land in silver light. Ahead, the tundra rolled on as far as Kruppe could see, flat and featureless. Then he squinted. Something had just appeared, still distant, walking with seeming great difficulty. He watched it fall once, then climb back to its feet. Despite the luminescence, the figure looked black.
(GotM p.355)
The Rhivi woman rocked the desiccated body in rhythmic motion, chanting softly. Water stained the Rhivi's thighs.
'Aye,' Kruppe whispered. 'She prepares to give birth in truth.'
Abruptly, the Rhivi tossed away the body. It crumpled in a lifeless heap.
The moon now hung immediately overhead, so bright that Kruppe could not look at it directly.
. . .
'K'rul, what of the first child within the Rhivi?'
'There was none, Kruppe. The Rhivi woman was prepared in a manner unknown to any man. Including myself. This sorcery belongs to the Moon, Kruppe.'
They continued watching the labours of birth. To Kruppe it seemed they waited more hours in the darkness than any normal night could hold. The Moon remained overhead, as if it found its position to its liking - or, he reconsidered, as if it stood guard over them.
(GotM p.358)
(It being about 5 years since my last GotM re-read, I'm proud I remembered these.)
This could be the influence of Ardata -- we know that she's got deep association with the moon due to the events in TBH. Again, quotes:
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'And now,' Mogora said, 'time for the moon.'
The blackness overhead vanished in sudden bloom of silver, incandescent light. Squealing, Iskaral Pust fell onto his back, so alarming was the transformation, and he found himself staring straight up at a massive, full moon, hanging so low it seemed within reach. (TBH p.363)
'Are you an Elder Goddess? I believe I know you . . . This vast web, the unseen pattern amidst seeming chaos. Shall I name you?'
'Best you did not. I have since learned the art of hiding.' (TBH p.399)
Seems a no-brainer. However, we later have the following passage from Hanavat in DoD:
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The existence of two moons may not be a new detail, but it's the first time I've noticed it. Looks like the nearest one has been destroyed by the JGs, while the second fainter one in a more distant orbit. The latter seems to fit with Ardata's MO, given her inscrutability is one of her defining features. In addition, the nearest moon has been slowly radiating pieces while Nightchill's soul is, as they said, "scattered to the winds". Either way, I can't think we got a passage that elaborate for no reason.
Interesting here is the intimation that the primary moon is still caught up in the "web," and betrayal by the sister moon is mentioned. In the prologue to MoI Nightchill states that her downfall would be by betrayal and nothing else. Originally this appeared to begin and end with Tayschrenn, but now I'm thinking Ardataphobia had a hand in it as well. I get the sense she's got at least as many hooks out as Shadowthrone (but better at hiding it, which is a lot easier when you rarely show up in POV chapters).
That said, I have no clue what the rest of the Barghest myth means. Night here appears as female, and Darkness as her lover, which I guess is possible of either Draconus (since being related never stopped any of the other gods) or Mommy D in her Awesome Phase. I doubt the Draconus connection, though -- by the time of the MoI prologue he and Nightchill hadn't seen each other in millenia.
Thoughts?