The Anglo-Saxon Solar Calendar

The Anglo-Saxon Solar Calendar

This is a purely notional calendar that I have invented, based upon various known aspects of solar calendars in the past and traditions in England, many of which still survive today. This page explains how the calendar is structured and my reasons for this. It is not intended to be a proposal for calendar reform, which I have detailed elsewhere, but more for personal interest.

How it works

The ancient Anglo-Saxon calendar was reputed to be a luni-solar calendar, following the cycles of the moon and adding an extra month every few years to keep it in line with the seasons. This calendar was reputed to have its new year on Christmas Eve. However, this would not be possible every year if the calendar were luni-solar, due to the lunar year not matching the solar year. It is thought that the 12 days of Christmas may have been epagomenal days added at the end of the year to compensate for this but this is speculative.

The calendar I have devised, however, is a solar one using Anglo-Saxon month names, in a similar vein to Tolkien’s Shire calendar. It is purely solar, with either 365 or 366 days depending on whether the year is common or leap, and the year starts on or around the date of the winter solstice.

Structure of the calendar

The calendar is structured so that each subsequent quarter begins on or near the remaining solar events of the year, i.e. the vernal equinox (Ostara), the summer solstice (Litha or Lithe) and the autumn equinox (Mabon). To reflect the different lengths of the seasons, the autumn and winter months have 30 days, apart from Solmonath, which has only 29 days. The spring and summer months have 31 days, except in leap years when Weodmonath has 32 days. The following table shows the months with their lengths and their usual start dates in the Gregorian calendar. These dates can vary by a day or so either side of the given dates due to the different cycles of leap years between the two calendars.

Leap Years

Traditionally, a leap year occurs when there are 366 days between winter solstices. However, in the modern calendar an arithmetic leap rule is used to calculate the date of the start of each calendar year, and whether it is a leap year or not. This rule is a "relatively" complex rule (although less complex than an astronomical calculation) called the LASSY (Linear Approximation to the South Solstice Year), devised by Dr. Irv Bromberg of Toronto University. This rule is relatively complex because, in the present era, it is not possible to employ a simple arithmetic rule to approximate the date of the south solstice (i.e. the December solstice, or the winter solstice in the northern hemisphere). The reasons for this are explained under "More on leap years" below. At present it will suffice us to know that the next few leap years are 1571 (2014-15), 1575 (2018-19), 1579 (2022-23) and 1583 (2026-27).



Usual starting dates


Afteryule (Aeftergiuli)
21 December
Solmonth (Solmonath)
20 January
Rethemonth (Hrethmonath)
18 February
Ostermonth (Eostremonath)
21 March
Thrimilch (Thrimilci)
20 April
Forelithe (Aerlitha)
21 May
Afterlithe (Aefterlitha)
21 June
Wedmonth (Weodmonath)
22 July
31 {32}
Holimonth (Halegmonath)
22 August
Wintering (Winterfylleth)
22 September
Blotmonth (Blotmonath)
22 October
Foreyule (Aergiuli)
21 November


The epoch for the calendar is the year 444 C.E. and the era is called A.S.E. (Anglo-Saxon Epoch). The years are therefore approximately 444 years behind those of the Gregorian calendar.

Days of the week

The days of the week were named after Norse deities, apart from Saturday, Sunday and Monday, and have the same origins as the names that are still used today. The Old English names for the days of the week were: Sunnandæg, Monandæg, Tiwesdæg, Wodnesdæg, Þunresdæg, Frigedæg, and Sæternesdæg.


The main festive days observed in the calendar are as follows, with typical equivalent dates in the Gregorian calendar:

  • 1 Afteryule (21st December)
  • Mid-winter, 15 Solmonth (3rd February)
  • Ostara, 1 Ostermonth (21st or 20th March)
  • Egg Moon/Ostern (Movable – first full moon of spring)
  • Mid-spring, 16 Thrimilch (5th May)
  • 1 Afterlithe (21st June)
  • Mid-summer, 16 Wedmonth (6th August)
  • Harvest Moon (Movable – last full moon of summer)
  • Mabon/Harvest Home, 1 Wintering (22nd September)
  • Mid-autumn, 16 Blotmonth (6th November)

Calendar for 1569 (2012-13)

In popular parlance, the Harvest Moon is the full moon closest to the autumnal equinox, therefore it could occur in the last half of Holimonth or the first half of Wintering. In more northern climes, however, harvest would tend to occur earlier than this, therefore in my calendar it is the last full moon before the equinox. This means that it will usually fall in the month of Holimonth, which interestingly enough, had at one time the alternative name of "Harvestmonth" (Hærfestmonað).

More on leap years

The calendar needs a set of rules so that it can be worked out which years should be leap and those that shouldn’t, based on the date and time of the winter solstice. One way is to use an algorithm to estimate the moment of the winter solstice, also known as the south solstice as it is when the sun reaches its farthest point south in apparent motion through the sky during the year. Unfortunately, such algorithms tend to be very complex, and get less accurate as they predict events further into the future due to the uncertainties surrounding the future motions of the planet in its orbit around the sun.

Another method is to use an arithmetic leap rule. This suffers from the same uncertainties regarding accuracy as related to future events, but at least has the merit of being simpler. But here we have another problems. The lengths of the seasons fluctuate all the time. Some are getting longer, some shorter and by different rates, all determined by the irregularities of the Earth’s orbit over long periods of time. At the present time, the vernal equinox (hereafter called the northward equinox) and the summer, or north, solstice are relatively stable and can be approximated using relatively simple algorithms. The autumnal, or southward, equinox, and the south solstice are less easily approximated, however, as they are currently changing at a greater rate than the other two.

Therefore, if we wish to use an arithmetic solution, we have to use a variable, or progressive, rule, rather than a fixed one. In the case of the south solstitial year, i.e. the year between two south solstices, this was relatively stable up to around 1500 CE, is currently getting shorter at a relatively high rate, and will stabilise again around 9000 CE. The rule employed therefore uses a linear approximation of the downward curve of the mean south solstitial year length during this period. It is not as simple as the fixed rules, but is simpler than the astronomical algorithm required to do the same thing.

The rule employed is called LASSY, standing for Linear Approximation to the South Solstitial Year, and was devised by Dr. Irv Bromberg of the University of Toronto. Dr. Bromberg has devised several leap rules for use with experimental or notional calendars, in particular his Symmetry454 calendar, a calendar that uses a "leap week" instead of a leap day to keep it in synchronisation with the seasons. I have used his freely available algorithm to work out the start dates for my calendar for the A-S years 1 to 2556 (i.e. 444 to 3000 CE), with the offset parameter adjusted to -10.95, which appears to give the closest approximation to the date of the south solstice. This takes into account the six hour difference due to the fact that the Anglo-Saxon days begin at 6pm rather than midnight, and therefore if, for example, the solstice occurs at 5pm on 21st December then the new year beings at 6pm on the 20th. If the solstice occurs at 7pm on 21st December then the new year begins at 6pm on 21st December. I have checked as many of the resultant start dates against approximated solstice dates and so far these have proved to be correct, so the rule is so far proving to be pretty accurate. Click here for a listing of the new year dates as calculated using the LASSY rule for the 21st Century (in PDF format).

More Information on this subject, see the links below. I am extremely indebted to Dr. Bromberg for the information and the algorithms that he has made freely available on his web site, which have enabled me to employ this leap rule to my calendar. The graphs and diagrams are worth a look on order to gain an appreciation of how the orbital mechanics of the Earth work, and how these factors must be taken into account when devising a calendar.

Alternative Anglo-Saxon Calendar

An alternative to the above traditional calendar, for those that like neatness, is one where the months all have 30 days, with an extra “month” of five or six days in the middle depending on whether it is a leap year or not. The structure is as follows:

  1. Afteryule (30 days)
  2. Solmonth (30 days)
  3. Rethemonth (30 days)
  4. Ostermonth (30 days)
  5. Thrimilch (30 days)
  6. Forelithe (30 days)
  7. Lithe (5/6 days)
  8. Afterlithe (30 days)
  9. Wedmonth (30 days)
  10. Holimonth (30 days)
  11. Wintering (30 days)
  12. Blotmonth (30 days)
  13. Foreyule (30 days)

The leap years take place in the same years as in the traditional calendar.

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