Stellar aberration is the phenomenon whereby the observed angular position of a star depends on the relative motion between the star and Earth. Specifically, a telescope must be tilted slightly into the direction of motion of Earth relative to the star. There are in fact three different angular positions of interest: the observed position of the star from Earth, the actual position of the star (at the instant of observation) as measured using Earth's clocks and rulers, and the actual position of the star (relative to Earth) as measured using the star's clocks and rulers. Clear diagrams show that none of these three angular positions are in general equal to each other, and help explain why the effect in practice depends only on Earth's motion and not on the star's motion, in apparent violation of the relativity of motion.