A shadow is merely a region where light is blocked, not a physical object or particle with mass, so its apparent movement is not limited by the speed of light.
The claim that a shadow can move faster than the speed of light is a well-established physical reality of kinematics and everyday observation, requiring no formal academic citation. Shadows are not material objects or information-carrying signals; therefore, points of intersection or absence of light can sweep across a distant surface at arbitrarily high speeds (such as a laser dot swept across the moon or a shadow cast across a light-years-wide surface). None of the retrieved papers directly address or test this basic optical phenomenon, rendering formal citations unnecessary as it constitutes common knowledge.