I make up most of the universe yet you cannot see me I'm everywhere and nowhere yet you can't touch me I'm what looks like a shadow and known by all If i ceased to exist life would stall What am I

I follow the line of maximum depth within a moving channel. Unmarked, continuous, defined only by gradient and flow. Political borders defer to me, though I remain entirely water. Trace the river’s lowest vector, and you arrive.

I go through phases, yet I always stay the same. What am I?

Horses are pointless. I'm a mythical white version, with a point.

In the night sky, dark and gloomy, appear dimly lit 'orbs' fluttering here and there seeking a light source for the next 'morrow night.