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Established 16/3/2000
MoonFinding Easter at KnowthMoon



there is a theory that the midwinter sun shines into the chamber of newgrange exactly on the shortest day of the year. many people know this 'for a fact', and could prove it to you by taking you out to bru na boinne on the 21st december, and - advanced bookings and local weather conditions permitting - showing you that this is so.

the fact is that the sun shines in to the newgrange passage for several days before and several days after the winter solstice. if you believe that newgrange was a deliberate and accurate construction (and i do) you will need to be more precise. you will need to be aware that there was no december 21st in neolithic ireland. you will need to be aware that the modern 22nd of december can also fall on the (astronomically identifiable) winter
solstice (in the northern hemisphere). you will be wise to remember that the year is 365 and 1/4 days long - and for this reason the 365 and 366 day intervals between the newgrange events mean that no two of the newgrange sunrises are ever exactly one year apart, nor can be.

Diagrammatic plan of Newgrange
Diagrammatic plan of Knowth

Diagrammatic plan of Newgrange (Click to enlarge)

Diagrammatic plan of Knowth (Click to enlarge)

you will then need to remember that the sun set a little further to the south in the period when the passage mound was built, sometime around 3150 b c. you would need a basic computer astronomy programme to indicate the angle of the sunrises on the horizon in that era. these programmes are cheap, popular, and nowhere nearly as complicated to use as they sound.

finally, having done all of that, you would need to show that the focus of the construction was to identify the sunrise that was closest to winter solstice sunrise, rather than to give a 'window' of a certain number of days either side of the solstice.

such a 'window' existed, and, though it has changed with the passage of time, still exists. it has the value that in uncertain weather, the approach and departure of midwinter could be monitored, even though the day itself dawned sunless. in 3150 b c this would have extended form 15 days before the solstice to 15 days afterwards. this leaves open a second interpretation of the newgrange passage - that it was focussed to answer the question :

" which new moon (or full moon) is the first of the new year ?".


familiarity with our own calendar sometimes makes us oblivious to its eccentricities. our system of european union bank holidays has added to, but failed to obliterate, the seasons of the churches' year. the main christian feasts are christmas - a fixed feast with regard to the calendar year - and easter - a moveable feast with regard to the calendar year. church seasons such as advent and lent are then fixed according to these fixed or moveable dates.

the exact date of easter was a source of doctrinal dispute over several centuries. it was one of the issues between the roman catholic church and the 'celtic church' tradition. but for all the disputants easter had a formula that was based upon the first full moon to follow the vernal equinox, as did the jewish passover from which the christian tradition arose.

so was newgrange constructed to mark a feast or festival of a fixed nature - or to identify a particular phase of the moon, a full or new moon moveable feast ? we do not know.


one pointer would be if the passages at knowth also admitted the sun. the rising sun moves along the horizon from south east to north east as the year proceeds. half way between is the spring equinox. how neat it would be for the supporters of the fixed feasts if the passages at knowth faced due east and due west to the rising
and the setting of the equinoctial sun !

many have hoped this, or even fudged the data to try and make it so. but the truth is different . the days at which the very long and narrow - and thus very accurate - knowth passages point are : six days from the equinox dawn( knowth east) and eighteen and a half days from the equinox dawn (knowth west). this apparent
waywardness, after the very precise focus of newgrange, has been a source of bafflement to many, and would have remained so if a connecticut retired doctor had not come up with a solution - the only one put forward so far.

Knowth Sketch Plan


the solution rests upon the neolithic builders of knowth being a culture which counted the passage of time in lunar months. this is not a big assumption - it would be most anachronistic to expect them to have evolved any division of time other than the natural one. they also dwelt within a mile or two of the tidal reaches of the boyne
estuary, where the tides faithfully keep lunar, not solar time.

the connecticut doctor, charles scribner, pointed out the possible significance of two days -' vernal equinox plus six days' - and 'vernal equinox minus eighteen and a half days'.

if you habitually measure out the year in lunar months - as do the native americans, the jews, and many well documented cultures - these two days on which the sun is aligned with the knowth passages are :
first : knowth east (equinox plus 6) : three synodic lunar months before the summer solstice - six synodic lunar months before the autumn equinox, and nine synodic lunar months before the eve of winter solstice, respectively . second : the passage of knowth west is thirteen synodic lunar months before the following vernal equinox .

all of these figures are for the period around 3300 b c. this has to be said because the lengths of the seasons vary in a slow cycle over the millennia.

so this is how you can identify in advance the christian church moveable feasts of the following year using knowth : observe the sun reaching the passage of knowth west - the one that is still open - in early spring.
there are now 13 moons until the following year's vernal equinox. now, after dusk falls, observe the day of the moon. if full moon is to follow in two days time then the following year's 'paschal' full moon, the one that
defines easter, will be two days after march 21st or wherever your vernal equinox is falling in that year of that era.

this could, like the newgrange orientation, be a coincidence. but when the opposite passage at knowth east can be 'read' to predict the other three of the four points of the year (as they stood with the season lengths
of 3300 b c or thereabouts ) - the odds lengthen.

Kink in Knowth west

A plan of Knowth West showing the kink in the passage.

knowth west also has a kink in the passage. the inner few metres may represent a slightly earlier passage incorporated into the mound. the case is immeasurably strengthened when it is found that the orientation
of the inner passage, if projected beyond the mound, would admit the sun on a date that is ten and a half days after equinox - or twelve synodic lunar months before the following equinox. this too, if it admitted light, could
be used to predict the date of easter of the year to follow.


thus it is a fact that both knowth and newgrange could be used to identify lunar or 'moveable' feasts. it is however like finding an abacus. simply because a calculation can be performed on an ancient abacus it
does not follow that that calculation was the original purpose of its maker. - to suggest that it was, can only be speculative.

nevertheless, the still intact and open passage of knowth (west) still functions to admit the light and foretell the full moon of easter thirteen months ahead. this function is less affected by the passage of the millennia than the functions of knowth east or of newgrange itself. to predict a festival in advance is also of more practical value than merely to mark a solstice or equinox as it occurs. irish weather makes such prediction vital , for - as many know to their cost - a midwinter morning can choose to be overclouded.

Kerb 15 by Richard Moore

Kerbstone 15 from Knowth painted by Richard Moore


there may still be a few conservative scholars who would be reluctant to give scandal to the faithful by admitting that the festival of easter is not of christian origin - but this fact is already apparent from a cursory reading of the gospels themselves. there may even be a lingering prejudice against the darkness, the moon, and the number thirteen - it all smacks too much of halloween and the fairies. but this does not excuse the researcher from taking a rational and consistent view.

as things stand at the present, we neither accept nor reject the orientations of the bru na boinn passages, but make a marvel of one while dismissing another two that are considerably longer and thus more precise. is newgrange a solitary anomaly among passage mounds ? a clock with only one hand ? a bell that strikes but once a year ?

knowth, is an older, more decorated, more complex passage mound than newgrange. the instincts of the archaeologists point to an equinoctial connection. they should trust their instincts and persist with this line of enquiry. there is more to discover. newgrange is neither the earliest marvel at bru na boinn nor the only one.

it would be a shame to deny knowth her share of the glory, her day in the sun.

Calendarstone: See how the Metonic cycle was recorded on a 5,000-year-old stone at Knowth.
Lunar stone: More lunar calculations at Knowth.

All information and photos, except where otherwise stated, copyright, © Anthony Murphy, 1999-2015
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