Does Auriel's Bow Count as a Daedric Artifact?

With the Unofficial Skyrim Patch, Auriel's Bow counts as a Daedric artifact for the Oblivion Walker achievement, despite the fact that it is an Aedric, not Daedric, artifact, and is therefore tied to the plane of Aetherius, rather than the planes of Oblivion.

Which Daedric artifacts are missable?

Missable Daedric Artifacts

Ring of Hircine from the quest "Ill Met by Moonlight." Killing Sinding prior to the quest while he is in his Beast Form will not let you begin the quest. The same applies to the Savior's Hide. Skull of Corruption from the quest "Waking Nightmare." It is only obtained if Erandur is killed.

What does shooting the sun with Auriel's Bow do?

"Shrouds the sun in sudden darkness when shot with Auriel's Bow" Shooting a Bloodcursed Elven Arrow from Auriel's Bow at the sun will cause a shroud of darkness around the sun, which will dissipate to reveal a black hole-like anomaly replacing the sun.