29 July, 2008

Litha (July) and Trilithi: the early English calendar

Before they converted to Christianity and adopted the Roman calendar, the early English (‘Anglo-Saxons’) reckoned time using a system of lunar months. Each cycle of the moon, probably from full moon to full moon, was a month. The year began at the winter solstice, the shortest day of the year. There were two seasons, summer, when the days were longer than the nights, and winter, when the nights were longer than the days (See my earlier post for a summary of the early English calendar.)

The sixth and seventh months of the year, corresponding approximately to the Roman and modern months of June and July, were called Litha. Like its counterpart in the winter, Giuli (from which we get the word Yule), Litha was a double-length month, or two months of the same name, placed either side of the midsummer solstice. See my June post for the possible meaning of Litha.

Bosworth and Toller’s Old English Dictionary says that the first Litha month (corresponding roughly to modern June) was called “se aerra Litha” and the second one was called “se aeftera Litha”. Kathleen Herbert says that the information in Bosworth and Toller comes from Bede’s treatise On the Reckoning of Time, and from later English scholars who commented on it such as Aelfric and Bryhtferth (Herbert 1994). The distinguishing terms ‘aerra’ and ‘aeftera’ aren’t in Bede’s account, so I presume they come from one of the later commentaries, but I haven’t verified the source. As I understand it, the meaning is closer to “the earlier Litha” and “the later Litha”, rather than “the month before Litha” and “the month after Litha”, so “Litha” refers to the name of the months and not to a date that occurred at the junction between them.


Bede, writing in 725, tells us:

When an embolismic year occurred (that is, one of 13 lunar months), they assigned the extra month to summer, so that three months together bore the name “Litha”, hence they called the year “Trilithi”.
--Bede, On the Reckoning of Time, Chapter 15. Translated by Faith Wallis.

This neatly demonstrates both the problem with a lunar-solar calendar and the early English solution to it. A solar year refers to one complete cycle of the sun from one midwinter solstice (or any point of your choice) to the next. This is a natural way to reckon time in an agricultural society living at temperate latitudes, where day length would be an important determinant of agricultural activities. But it is rather long to be the only unit used to measure time.

The lunar month, covering a complete cycle of the moon from one full moon (or any other point of your choice) to the next, is a shorter unit of time, conveniently intermediate between the long unit of the solar year and the short unit of the solar day. Thus a lunar-solar calendar gives you three units of time each of a different order of magnitude, so you don’t have to express time periods either in tiny fractions of a year or in very large numbers of days. Great.

Unfortunately, the problem is that none of these natural units of time are exact multiples of each other. A lunar month is 29.53 days. A solar year is 365.24 days. There are 12.37 lunar months to a solar year. So the lunar months won’t line up neatly with the solar year. Suppose you start your lunar-solar calendar at a time when the full moon also falls on the midwinter solstice, so both the year and the first month of the year start on the same date. The second month of the year starts at the next full moon, the third month starts at the full moon after that, and so on through the year. But 12 lunar months only take 29.53*12 = 354.37 days to complete. So by the time the next midwinter solstice comes round, at 365.24 days, the moon is already 10.87 days past the full. What do you do? Do you start the new year when the moon was full? In which case the year won’t match the solstice. Or do you start the first month of the new year at the solstice? In which case the months won’t match the phase of the moon.

I can imagine priests, druids and learned folk tearing their hair out over this infuriating astronomical feature. Some cultures settle on a purely solar calendar and let the months go out of phase with the moon (our modern Western calendar does this), others settle on a purely lunar calendar and let the year go out of phase with the sun (the Islamic lunar calendar does this). Others adopt a hybrid system, adding an extra month when necessary to bring the lunar months back into line with the solar year – a sort of “leap month”, if you like, in the same way as the modern Western calendar adds a day (almost) every four years to keep the calendar synchronised with the solar year. This extra month is called an intercalary month.

Clearly the early English applied this hybrid approach, adding an extra month to Litha to keep the lunar months in line with the solar years. This would happen every two or three years (every 2.72 years to be precise), so a “Trilithi” year would be pretty common. It could have been decided by calculation, by observation, or a mixture of both. If you kept a count of the observed full moons starting at the midwinter solstice each year and the second Litha full moon happened before the midsummer solstice, you would know it was a Trilithi year. If you also kept a count of the days and alternated between 29 and 30 days for a lunar month, you could calculate the date of the full moon even if the weather was too cloudy for a direct observation.

Bede: The Reckoning of Time. Translated by Faith Wallis. Liverpool University Press, 1999, ISBN 0-85323-693-3.
Herbert, Kathleen. Looking for the Lost Gods of England. Anglo-Saxon Books, 1994. ISBN 1-898281-04-1.


Rick said...

'After' still occasionally has the sense of 'latter part of' rather than 'following' - e.g., the afterdeck of a ship. (But note how many archaic word forms survive in nautical language!)

I assume that aerra just barely survives in modern English as poetic 'ere.'

Bernita said...

Summer coming and going when there was no need for precision.

Carla said...

Rick - Yes, poetic 'ere' is from 'aerra'.

Am I right in thinking that nautical terminology is especially conservative? The Roman navy retained a lot of Greek terms, didn't it? I suppose sailors have a stronger reason than most to never, ever change their terminology. When you're handling a sailing ship in a storm and hauling on the wrong rope - or on the right rope ten seconds too late - will give you all a one-way ticket to Davy Jones, you can't afford the risk of having two names in use for the same thing.

Bernita - for practical purposes 'summer' no doubt depended on the vagaries of the weather just as much as it does today.

Rick said...

Nautical language does seem especially conservative, though the Roman use of Greek terms may be because 'Roman' seamen were largely Italiot Greeks. Otherwise your explanation makes sense, but I suspect that nautical language also helps distinguish salty dogs from mere landlubbers.

The terminology is wonderfully old! I don't know whether merchant seamen still ship 'before the mast,' but the term has to go back before c. 1450, to a time when English ships had only one mast. 'Forecastle' is definitely still in use, though raised foredecks ceased to be defensive 'castles' in the 16th century.

Alianore said...

Fascinating post, Carla!

Gabriele C. said...

Lol, I can imagine a gathering of confused druids trying to make sense of the mess.

Druid 1: You put that second stone wrong and that's why there is no moon shining through the cleft tonight.

Druid 2: Nay, I put it right where the sun will be highest tomorrow midday.

Druid 1: You stupid git should count the moons.

Druid 2: That's so yesterday. It is sun years now.

Chief Druid *phones Belenus*: Hey, can you perhaps get the moon and sun cycles in sync? My colleagues are about to come to blows over it.

Belenus: Mwuhahah

Druid 1: See, I'm right.

Druid 2: No, you ain't.

Druid 1: Am.

Chief Druid: Stop it.

Belenus *creates lunar eclipse* Mwuahaha

Druid 2: And now your precious moon is gone, neiner, neiner.

- Continue like that the rest of the night.

Carla said...

Rick - Yes, specialist language as a way of distinguishing members of a group from those who aren't! Most crafts and professions have something similar - medicine and law leap to mind. It's partly a professional shorthand that provides a concise and precise description to people in the know, and partly a handy barrier to outsiders.

Alianore - thanks.

Gabriele - ha! And not just the rest of the night, the rest of the year, century, millenium.....
Have you read Stonehenge by Bernard Cornwell? He has Stonehenge being built partly as a priest's attempt to persuade the gods to fix the mismatch between the solar year and the lunar months. Needless to say, they didn't pay any attention :-)

Gabriele C. said...

I've read Stonehenge but I must admit it's the weakest book Cornwell has written, imho.

Carla said...

Yes, he's written better :-)

Meghan said...

Once again tons of information that is completely new to me. Thanks Carla for the great info!

Carla said...

Meghan - thanks