>>18808399can you imagine a flat plain that is tangential to a point on a sphere? you know like when a ball lies on the ground but the other way around.
the ground is the tangential plain, it touches the ball on 1 point.
now imagine it the other way around. you hold a ball and move the point on which the tangential plain touches it across the surface of the sphere.
okay champion last step: this tangential plain is now a mirror.
the line from light to dark side of moon is the line of points on which the mirror faces a direction that gives you no line of sight to be the sun.
or to be short: light is reflected by moon.
