Look up on a clear autumn evening in the northern hemisphere, and you will immediately recognize the five bright stars of Cassiopeia tracing a distinct W across the sky. For most of human history, this geometric simplicity was assumed to represent a physical reality. Early observers working within the model of a celestial sphere believed these stars were genuinely connected, sitting close together on a fixed crystalline shell. This episode explores how that assumption was tested and ultimately overturned by the slow accumulation of astronomical measurement.

We follow the history of stellar parallax, from Friedrich Bessel's patient observations in the nineteenth century to the precise astrometric data gathered by the Hipparcos and Gaia space missions. These instruments revealed that the five stars of the W—Caph, Schedar, Ruchbah, Segin, and  ...