Prior to general relativity, one could rely on a rigid frame of reference such as the earth and extend it throughout space to define relative motion.

Weyl notes that what we seem to observe as the rotation of the stars, is in reality not the rotation of the stars themselves but the rotation of the “star compass” [Sternenkompass] which consists of light signals from the stars that meet our eyes at our present location from a certain direction. It is crucial, Weyl reminds us, to be cognisant of the existence of the metric field between the stars and our eyes. This metric field determines the propagation of light, and, like the electromagn