Bodleian Library, Ashmole 370 is an astrological / medical manuscript written in England in 1420 ca. At f25r, it features a beautiful Lunar volvelle, whose structure and function are clearly described by Timothy J. Mitchell in Binding the Heavens: Deconstructing the Lunar Volvelle (2018).

I propose a digital animation reconstructing the individual components of the volvelle and their movement.

One of the functions of this volvelle is to graphically compute the phase of the moon on the basis of the current position of the sun and the moon. The tool includes four concentric components:

1. A base marked with the cardinal directions and the hours of the day; this is the only fixed component, all the other circles can be turned around the central pivot.

2. The zodiac and the months. The winter and summer solstices are prominently marked by a black and a red cross respectively. The months circle is marked by 365 small white and dark squares, corresponding to the days of the year. The zodiac is marked according to its 360 degrees.

3. A sun circle, with a large pointer used to set the wheel according to the current position of the sun with respect to the zodiac. This circle is split into 29 segments corresponding to the days between the occurrences of two new moons. The inner part of the sun circle is painted with a shape that, when seen through the circular window in the moon circle, visually approximates the phase of the moon.

4. The moon circle has a large pointer with the same shape and function as that of the sun. The circular window shows the current phase of the moon. In particular, when the sun and the moon are in conjunction (i.e. when the two pointers overlap), the circle is all black (new moon); when they are opposite, it is all white (full moon).

The inscription at the bottom of the page reads:

“In the yeer ther beth CCC daies lx and fyve.”

In the year there are 365 days.