Elder Scroll (Sun)

The Elder Scroll is a quest item located in, where it is central to the main quest.

Background
According to Valerica, the scroll reveals that "The Blood of Coldharbor's Daughter will blind the eye of the Dragon". This refers to the Tyranny of the Sun, an ancient prophecy that foretells the eternal beclouding of the sun.

This scroll was originally in the posession of Valerica, Lord Harkon's estranged wife. She took it from Castle Volkihar some time in the early First Era and hid it, along with her daughter Serana in Dimhollow Crypt so that Harkon could not complete the prophecy.

Awakening
The Dragonborn uncovers Serana and the Elder Scroll in Dimhollow Crypt. He is then tasked to return her back to Castle Volkihar.

Prophet (Dawnguard) and Prophet (Vampire)
The Moth Priest, Dexion Evicus gives a reading of the scroll:

''"I see a vision before me, an image of a great bow. I know this weapon! It is Auriel's Bow! Now a voice whispers, saying "Among the night's children, a dread lord will rise". In an age of strife, when dragons return to the realm of men, darkness will mingle with light and the night and day will be as one.

The voice fades and the words begin to shimmer and distort. But wait, there is more here. The secret of the bow's power is written elsewhere. I think there is more to the prophecy, recorded in other scrolls. Yes, I see them now... One contains the ancient secrets of the dragons, and the other speaks of the potency of ancient blood.

My vision darkens, and I see no more. To know the complete prophecy, we must have the other two scrolls.''"

Unseen Visions
The Dragonborn is required to read the Elder Scroll at Ancestor Glade in order to locate Auriel's Bow.

If the Dragonborn sided with the Dawnguard, the scroll, along with the Elder Scroll (Blood) can be sold to Dexion Evicus for 6,000 after completely finishing the main quest.

Quests

 * Awakening
 * Unseen Visions