Board Thread:Lore Discussion/@comment-68.45.229.57-20130720115140/@comment-3186827-20131017091344

AzuraKnight wrote: The full prophecy Harkon was going for permanently blocks out the sun and involves Serana's (or her mother's maybe) death, copy/paste from the wiki page -

"The inscription denotes a ritual that requires a Daughter of Coldharbour as a sacrifice and the bow of Auri-El to permanently purge the world of sunlight."

We're not fulfilling the prophecy as Harkon would have just a smaller ritual based on it to get the effect for a limited time. This is the closest correct answer. The big ritual Harkon planned would have been permenant darkness as the sun (a big hole to Aetherius) would be sealed. The smaller ritual with the arrows the Dragonborn does is reshaping the prophecy as revealed in the quest journal:

With Auriel's Bow in my possession, it's time to confront Harkon and reshape the prophecy as I see fit.