Credit: ©The Royal Society
    Image number: RS.21059

    Perpetual calendar with astronomical data

    Object type
    Archive reference number
    height (sheet): 194mm
    width (sheet): 1488mm
    height (compartment): 97mm
    width (compartment): 62mm
    Content object
    Section from a folded medieval almanac, showing a perpetual astronomical calendar for January 1st to June 15th. Located on the exterior side of the almanac, below the cardinal fold when fully opened (24 compartments).

    Each complete month occupies four consecutive compartments. Rows of daily data for the first part of the month cover the full width of two compartments, followed by two compartments for the latter part of the month.

    Each compartment is divided into nine columns. The first compartment for each half of the month records (from right to left):

    1.The day of the month (in Arabic numerals)

    2.The dominical letter (one of seven letters A-G indicating days of the week, ‘A’ highlighted in red. On any given year if you know the date e.g. a Sunday or ‘domenica’ falls, every date marked with the same dominical letter will also be a Sunday etc throughout the weekdays).

    3-4. The day of the month according to the Julian calendar (organised by Kalends ‘KL’, Nones ‘Non’ and Ides ‘Idus’—across two columns, in the first column the day number counting down from the previous ides and in the second the abbreviations as noted).

    5. The Golden Number ‘aureus num’ (indicates the date of a new moon for each year in a 19 year lunar cycle. Calculated by dividing the year by 19 and adding one to the remainder the resulting golden number listed against a date in the calendar indicates the date a new moon will fall for years with that number).

    6. The duration of a half night ‘nox’ (period between sunset and midnight also equal to period between midnight to sunrise, hence half night and doubled will equate to total period of darkness. Given in hours (red ink) and minutes (black ink) the hour is only listed when it changes. Column topped with a figurehead in black ink).

    7. The duration of a half day ‘diem’ (period between sunrise and midday also equal to period midday and sunset – hence half day. Given in hours (black ink) and minutes (red ink), the hour is only listed when it changes. Column topped with a figure head in red ink. The values given for a half day and half night will always total twelve and allow for the calculation of the time of sunrise and sunset).

    8-9. Celestial latitude. In two columns under the heading ‘Sol’ with a symbol of the sun. In black ink the position of the sun on the ecliptic given in a degree of the thirty assigned to each sign of the zodiac (black ink) and minutes (red ink). Running continuously across the months this column also includes the name of the new sign of the zodiac at the point where the sun moves into the next sign and re-iterates the current sign at the top of each new compartment.

    The nine columns on the second compartment for each half of the month record the date, hour and minute in a year on which the conjunction of the Sun and Moon will occur for three 19-year lunar cycles.

    The first two folds that make up this side of the manuscript were left blank, possibly for the addition of notes and dates of personal or local significance (though this practice is more common in examples of later, annual almanacs from 1560 onwards1).

    Calendars on other parts of the almanac illustrate the signs of the zodiac and labours to be undertaken each month and a liturgical calendar - marking holy days in the Christian church calendar.
    Object history
    Robert Moray FRS donated the manuscript to the Royal Society library in 1668 (JBO/3/104: Journal Book, vol. 3 p.232). The provenance of the manuscript, before it came into the hands of Moray, is unknown.

    The presence of the feast day ‘Translacio Edwardi Regis’ (13 October) entered on the calendar as a red letter day shows an importance being attached to Edward the Confessor great patron of Westminster Abbey where his relics were a popular site for pilgrimage, this may suggest a London origin. While the inclusion of ‘Translacio Mildride’ (13 July) honouring the Anglo-Saxon princess Mildred, suggests Kent. Mildred was Abbess of Minster-in-Thanet, where she was first buried and her relics were later moved to Canterbury. Four Archbishops of Canterbury also feature in the liturgical calendar, strengthening the connection with Kent as a possible place of origin. The inclusion of cultivation activities early in the annual calendar of labours (digging/planting in February), a later hay harvest (July rather than June) and viticulture (March and September) suggests a temperate southern English climate in support of one of these locations rather than a warmer Mediterranean location or a cooler northern one.

    The calendar has been dated to the late 14th century based on the textual content and analysis of the pigments used. Saint George’s feast (23 April) written into the calendar in brown-black ink demarcating it as a lesser feast, indicates the calendar was produced before the elevation of the feast to a red letter day after the battle of Agincourt in 1415. Whilst the presence of the feast of St. Anne, which was not promulgated until 1383 suggests this as the earliest likely date. The presence of the yellow pigment orpiment supports a date in the late 14th century as it was widely replaced by use of lead-tin Yellow around 1400.

    An example of a mid-quality almanac. The range of pigments used demonstrate it was produced economically but not with the cheapest available materials. No gold leaf is present and indigo dyes are used for blue rather than more expensive minerals, however vermilion red is employed over cheaper organic sources. The uniformity and selection of pigments (gallo-tannic black rather than carbon-based) suggests that there was a single creator, rather than a scribe and an illustrator as would be expected for a finer document. This is borne out by the fairly crude rendering of the illustrative material and mistakes or omissions in the layout of information, see for example figures missing feet where these would have extended below a ground line and numbers missing from zodiac headings.

    Conserved in 2021 with the support of the National Manuscripts Conservation Trust.

    Video demonstrating the format of the almanack and relationship of the calendars available here:

    See P Robinson, 'A 'very curious Almanack'; the gift of Sir Robert Moray FRS, 1688', Notes and Records, 2008 vol 62 pp 301-314.
    Related fellows
    Robert Moray (1608 - 1673, British) , Natural Philosopher
    Associated place
    <The World>
       > Europe
          > United Kingdom
    Powered by CollectionsIndex+/CollectionsOnline