Decan 13: The Harvest Date Moved
Spica is the ear of grain in the Virgin's hand, and Hipparchus found the precession of the equinoxes by trusting a two-degree anomaly in his readings of it. Decan 13 is artistry and perfection: one crop, a rep a day, nothing else refined, and a harvest date that moved because the measurement said so instead of because the mood did.