To use the power of Auriel's bow you need either Sunhallowed Elven Arrows or Bloodcursed Elven Arrows. Shoot either arrow directly into the sun and it will either grow brighter if you use Sunhallowed Arrows or grow darker and red if you use Bloodcursed Arrows. You can get Sunhallowed Arrows by giving Knight-Paladin Gelebor Elven Arrows back where you first retrieve Auriel's Bow and you can get Bloodcursed Arrows by giving Elven Arrows to Serana. Using either arrow on the sun will give you the achievement "Auriel's Bow."
Added by: AK GMAN14 Jul 14th 2012, ID#8532