[Petty Dwarf]

Sauron's dominion wasn't built on actual darkness. Confusion, lies, betrayal, and ignorance put the "dark" in the Dark Years. Had the Fourth Age become covered in this "second darkness" the moon and sun would be in no more peril than they were in Sauron's last reign. But Sauron's industrial activities have a pollutant effect, so some actual darkening would go on, and probably did in the Second Age.

As for Morgoth attacking a celestial body, there is also the powerful version in Myths Transformed where he rapes Árië/Arien, spoiling the sun. In that one, a Round World version, the Moon is then created to bring light to dark places.

Also in MT, another Round World plot takes place just prior (7 years prior) to the awakening of the Elves. Morgoth creates a darkness over most of Middle-Earth which obliterates moon and stars, and dims day to a dusk at most. Manwë and Varda contest with westward winds, and the clouds are pushed back east, only to return. This goes on like a tug of war for a while, until Manwë unleashes a great wind and rends the veil for longer than usual. The Elves awake to these bright stars, which soon seem to receede into the West as the Cloud returns.