A Volvelle is a type of rotary device, often found in the pages of ancient manuscripts, used to show the relationships between different elements. In this case, we can use it to observe the relationship between the Sun, Moon and both standard and astrological calendars.
Much useful information is to be found here at Richard Wymarc’s page, which I recommend you read, since he describes the device very well: https://astrolabeproject.com/downloads/volvelle/deconstructing_the_lunar_volvelle.pdf
My 52° latitude Volvelle is based on the one in Richard’s document here; 52º is a standard latitude for instruments used in the UK. The 30° and 40° versions have been reworked by me to account for the different sun elevations and day/night lengths at those latitudes. If there’s enough interest, I may add more.
The main body of the instrument holds all the calendar information. There is a standard calendar and the Zodiac/Astrological calendar. These allow an easy lookup of dates when either pointer is used.
Above/inside the Zodiac ring is the Hours of Day/Night ring. These show the Day hours as the lower value of each pair, and the Night as the upper value. Original Volvelles showed the numbers as half the hours; you had to double them to make your reading, so I have simplified things here by just giving the actual value.
The innermost ring on the main disc shows the maximum elevation at noon of the Sun through the year. Lower latitudes will have higher Sun elevations, and vice versa.
I’ve also added a thin ring in between the Zodiac and Daylight Hours rings; this is to show the main Solstice and Quarterly festival dates throughout the year. These are of Celtic and Germanic origin, and make a nice way to follow the progression of the year.
Starting in December; YU = Yule (Christmas), IM = Imbolc, OS = Ostara (Easter), BE = Beltane (May Day), LI = Litha, LA = Lammas, MA = Mabon (Harvest) and SA = Samhain (Halloween).
The Sun disc has a scale of days around the edge; this is the number of days since New Moon and is 29.5 days in length, called the Synodic Month. It also has small pointers that show the quarter and half phase points.
The Moon disc has a hole cut into it, which shows the approximate Moon phase printed on the Sun disc underneath. It also has seven small pointers, representing the 1/6, 1/4 and 1/3 ecliptic points, which are important in Astrology.
Finding the Sun position: Simply align the Sun tab with whichever date (calendar or Zodiac) you wish to look up, and read off the corresponding date on the other scale.
Finding the Moon position: This is less simple and requires you to know how long past New Moon we are. In the photo above, the Moon is set at just over 9 days after New Moon and is just past quarter full.
Finding the date of the New or Full Moon is easy enough if you have a calendar. I subscribe to this Astro calendar which drops all the relevant dates into my calendar online: https://cantonbecker.com/astronomy-calendar-files/astrocal.ics
if you happen to own an Apple Watch, this lunar face is useful for seeing how many days past New Moon we are right now. Here it is 12 days; waxing gibbous.
You can also guesstimate the Moon’s position by simply rotating the dial until the Moon phase on the dial matches the Moon in the sky. Not very accurate, but it can be useful.
Finding the Solar Elevation: The Sun will rise higher into the sky during the summer than in winter, so by setting a pointer to the desired date, you can see how high it will rise on any given day. Using both pointers, you can see the range of the year during which the Sun will be above a certain elevation. This is useful if you wish to see when the sun will clear an obstacle, or for how long part of your yard might remain shaded.
Reading the time from the Lunar shadow on a Sundial at Night: It is possible to know the clock time if you have a bright enough Moon to cast a shadow.
To do this, first set the Moon dial to the current day past New Moon. Supposing the Moon’s shadow is showing 11pm on the sundial. Rotate both the Sun and Moon discs together until the Moon pointer is at 11. The Sun pointer will show the current time.
This is not the most accurate method of telling the time, and close to Full Moon it is hard to spot the slight changes in phase, so if you get the day wrong then you can be off by an hour for each day’s difference. (i.e if you’re 2 days past Full Moon, you’re two hours wrong). Also, the Moon moves through the sky fast enough, and its orbit is eccentric enough, that multiple errors are likely to creep in.
A final note
The Lunar Volvelle is a fascinating insight into how people worked with time and date in centuries past, and remains useful today as a quick lookup device for basic information about the Sun, Moon and time of year. I hope you enjoy using it.