The Emperor's Astronomy

A complex, hand-colored astronomical volvelle, which is a paper instrument with rotating parts, is mounted within an octagonal frame. At the top of the page, two disembodied arms in red sleeves emerge from blue-tinted clouds. They hold a set of interlocking gold and green rings that support the instrument. The outer octagonal frame is divided into twelve sections. Each section contains the name of a month and a numerical scale for days. Inside the octagon are several concentric, rotating paper disks. The largest central disk is colored yellow and features two crescent moons with human faces in profile facing each other. A red thread pointer is attached to the central axis. A smaller secondary volvelle with month abbreviations is attached to the upper left of the yellow disk. Various reference letters are positioned throughout the diagram to assist the user.

A small sub-dial used for finer monthly adjustments: MARCH APRIL MAY JUNE JULY AUGUST SEPTEMBER OCTOBER NOVEMBER DECEMBER JANUARY FEBRUARY

THE DEFERENT original: "DEFE RENS." This refers to the "carrying" circle in a planetary model that moves a smaller circle or a celestial body.

MINUTES FOR THE EQUATION OF DAYS original: "MINVTA EQVATIONIS DIERVM." These are the specific units of time used to reconcile the difference between solar time, which varies slightly throughout the year, and the steady time measured by mechanical clocks.

Volvelle: a paper instrument with rotating parts used for making astronomical or mathematical calculations.
Equation of days: the mathematical correction used to find the difference between apparent solar time and mean solar time.
Deferent: a large circular path in the Ptolemaic system of astronomy that carries another smaller circle or a planetary body.