The Great Darkness

[Kuruharan]

He destroyed the creations of the other Valar because of jealously and probably pride.

You are certainly right about that.

However, I must still agree with Formendacil that Morgoth wanted destruction over and above domination.

Sauron was challenged by Elves and Men and wiping out light would certainly cripple them.

Well, yes...that's why he did it. But the original question was whether he would maintain a perpetual physical darkness and I think that is unlikely.

[luthien-elvenprincess]

I don't think that Melkor or Sauron could ever achieve their entire goal.

...the Valar endeavoured ever, in despite of Melkor, to rule the Earth and to prepare it for the coming of the Firstborn; and they built lands and Melkor destroyed them;valleys they delved and Melkor raised them up; mountains they carved and Melkor threw them down; seas they hollowed and Melkor spilled them; and naught might have peace or come to lasting growth, for as surely as the Valar began a labour so would Melkor undo it or corrupt it. And yet their labour was not all in vain; and though nowhere and in no work was their will and purpose wholly fulfilled, and all things were in hue and shape other than the Valar had at first intended, slowly nonetheless the Earth was fashioned and made firm.

As seen from the above Ainulindale quote, none of the Valar's original and total purposes were ever fully realized, why would the purposes and designs of Melkor or Sauron be any different?

[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.