Answer:
You saw me where I never was and where I could not be. And yet within that very place, my face you often see.
A morbidly-named body of water
I pass before the sun, but make no shadow.
It holds most knowledge that has ever been said. But is not the brain, is not the head. To feathers and their masters, it's both bane and boon One empty, and one full.
What zips through the sky with a tail of fire and dust. It could be an omen, its origin to discuss?
It produces a flower but it is not its fruit; it produces branches which are its fruit.