In order to be observed with the naked eye, a spacecraft must reflect sunlight towards the observer; thus, naked-eye observations are generally restricted to twilight hours, during which the spacecraft is in sunlight but the observer is not.
A spacecraft must reflect sunlight towards the observer; thus. This is naked. This is to be observed with the naked eye. Eye observations are generally restricted to twilight hours. The spacecraft is in sunlight during twilight hours. The observer is not.