This is more of a D2 story related event, but I was just thinking how could a group of low life Claw Vipers be able to bloat out the sun and bring about an eclipse? I mean, isn’t that of a cataclysmic proportion? Imagine the world sunk in darkness for an extended time and the impact of that if such rituals happen more often and/or are not interrupted. Also, was there any explanation of what physically happened to the sun?
From the sounds of it, the darkness covered only the Aranoch desert area (so act 2 itself), rather than the whole world. Also according to Drognan, the claw vipers had done something similar in the past, centuries ago. So considering the great span of time in between, it’s likely something that takes an enormous amount of time and/or effort to pull off. Not to mention that the ritual required creating an altar, and should the altar be destroyed, the ritual ended. And considering we found the amulet of the viper (a piece that makes up the Horadric Staff), it’s likely that the ritual also requires a great deal of magic to start and maintained.
Now as for what physically happens to the sun during the quest, the game describes it either being an eclipse or the sun being captured. Personally I think it’s more likely the former rather than the latter, since capturing the sun would assumingly have catastrophic effect on the world. As such I think the Claw Vipers create a veil of darkness that covers the skies of the Aranoch desert.