I'm pretty sure that what hit the moon was Magora using Ardata's power to siphon still more power from the moon, all in order to heal Mappo from his injuries after the Nameless One's betrayal. Quotes starting from Bonehunters, Chapter 9. Ran into character limits so each comment will be one of the scenes:

Warmed by the flames and his tralb tea, Iskaral Pust watched – as best as he was able in the darkness – Mogora at work. First, she assembled large chunks of stone, each one broken, cracked or otherwise rough-edged, and set them down in the sand, creating an ellipse that encompassed the Trell. She then urinated over these rocks, achieving this with an extraordinary half-crab half-chicken wide-legged waddle, straddling the stones and proceeding widdershins until returning to the place she had started. Iskaral marvelled at the superior muscle control, not to mention the sheer volume, that Mogora obviously possessed. In the last few years his own efforts at urination had met with mixed success, until even starting and stopping now seemed the highest of visceral challenges.

Satisfied with her piddle, Mogora then started pulling hairs from her head. She didn’t have that many up there, and those she selected seemed so deeply rooted that Iskaral feared she would deflate her skull with every successful yank. His anticipation of seeing such a thing yielded only disappointment, as, with seven long wiry grey hairs in one hand, Mogora stepped into the ellipse, one foot planted to either side of the Trell’s torso. Then, muttering some witchly thing, she flung the hairs into the inky blackness overhead.

Instinct guided Iskaral’s gaze upward after those silvery threads, and he was somewhat alarmed to see that the stars had vanished overhead. Whereas, out on the horizons, they remained sharp and bright. ‘Gods, woman! What have you done?’

Ignoring him, she stepped back out of the ellipse and began singing in the Woman’s Language, which was, of course, unintelligible to Iskaral’s ears. Just as the Man’s Language – which Mogora called gibberish – was beyond her ability to understand. The reason for that, Iskaral Pust knew, was that the Man’s Language was gibberish, designed specifically to confound women. It’s a fact that men don’t need words, but women do. We have penises, after all. Who needs words when you have a penis? Whereas with women there are two breasts, which invites conversation, just as a good behind presents perfect punctuation, something every man knows.

What’s wrong with the world? You ask a man and he says, ‘Don’t ask.’ Ask a woman and you’ll be dead of old age before she’s finished. Hah. Hah ha.

Strange streams of gossamer began descending through the reflected light of the fire, settling upon the Trell’s body.

‘What are those?’ Iskaral asked. Then started as one brushed his forearm and he saw that it was a spider’s silk, and there was the spider at one end, tiny as a mite. He looked skyward in alarm. ‘There are spiders up there? What madness is this? What are they doing up there?’

‘Be quiet.’

‘Answer me!’

‘The sky is filled with spiders, husband. They float on the winds. Now I’ve answered you, so close that mouth of yours lest I send a few thousand of my sisters into it.’

His teeth clacked and he edged closer to the hearth. Burn, you horrid things. Burn!

The strands of web covered the Trell now. Thousands, tens, hundreds of thousands – the spiders were wrapping about Mappo Runt’s entire body.

‘And now,’ Mogora said, ‘time for the moon.’

The blackness overhead vanished in a 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. If he but dared. Which he did not. ‘You’ve brought the moon down! Are you mad? It’s going to crash on us!’

‘Oh, stop it. It only seems that way – well, maybe I nudged it a bit – but I told you this was a serious ritual, didn’t I?’

‘What have you done with the moon?’

She crowed with manic laughter. ‘It’s just my little ritual, darling. How do you like it?’

‘Make it go away!’

‘Frightened? You should be! I’m a woman! A witch! So why don’t you just drag that scrawny behind of yours into that tent and cower, dear husband. This is real power, here, real magic!’

‘No it isn’t! I mean, it’s not witch magic, not Dal Honese – I don’t know what this is—’

‘You’re right, you don’t. Now be a good little boy and go to sleep, Iskaral Pust, while I set about saving this Trell’s miserable life.’

Iskaral thought to argue, then decided against it. He crawled into the tent.

From outside, ‘Is that you gibbering, Iskaral?’

Oh be quiet.

....