Astronomy in Ireland from earliest times to the eighteenth century

Vol.26,pp.l-13, 1 9 8 2 Printed in Great Britain. All rights reserved.

0083-6656/82/010001-13506.50/0 Copyright © 1982 Pergamon Press Ltd.

Vistas in Astronomy,

A S T R O N O M Y IN IRELAND FROM EARLIEST TIMES TO THE E I G H T E E N T H C E N T U R Y Susan M. P. McKenna-Lawlor Physics Department, St. Patrick's College, Maynooth, Co. Kildare, Ireland

ABSTRACT Evidence that the builders of Irish passage graves and stone circles may have possessed some knowledge of basic celestial cycles is discussed. The introduction of Celtic culture to Ireland circa 600 B.C. is next described and an account of the astronomical learning of the Celts provided based on classical documentation and Irish vernacular sources. Following on the coming of Christianity to Ireland in the fifth century, the necessity to construct Easter tables led Irish monks to such related activities as establishing collections of computi, compiling Annals and undertaking studies of available astronomical material. In particular, through exposure to Helenistic writings, they understood celestial motions in terms of the Ptolemaic model and were recognised authorities in Europe in the eighth and ninth centuries on astronomical matters. The influence of the Viking and Norman invasions in disrupting the intellectual life of the country is then outlined and the circumstances relating to the creation of conditions leading to the brilliant flowering of Irish astronomy in the eighteenth century are elucidated. The first known evidence 7000-4000 riverside However,

of habitation

in Ireland dates from the period

B.C. These early settlers hunted salmon,

eels and water fowl from

sites where the remains of their wattled huts may still be found. nothing is known concerning the astronomical

food gathering mesolithic Archaeological

knowledge

of this

people.

and paleo-botanical

evidence

is found for the growth,

from

about the middle of the fourth millenium B.C.. of a new economy in Ireland. Domesticated crops

(wheat,

animals

(cattle, pigs,

sheep,

goats) and domesticated

barley) were introduced and it is clear that the implementation

of such farming activity must have provided a special incentive understand

the sky through observation.

some astronomical

awareness

associated with significant other relevant records, orientations

often oriented their buildings celestial phenomena.

it is of particular

of those many monuments

Into the first category

interest to analyze the

in Ireland dating from the Neolithic associated. examples

of two

namely the Passage Grave and the Stone Circle. falls the spectacular monument 1

A

in directions

In the absence then of

In the present text, I propose to look at representative kinds of Irish megalith,

to seek to

As we know, cultures with at least

and Bronze Ages to see if they might be astronomically

JPVA 26:1-

seed

of Newgrange

on the

2

S.M.P. McKenna-Lawlor

River Boyne, which is known from radiocarbon dating to have been constructed around 2500 B.C. This tomb consists, a passage and a chamber,

as the name Passage Grave implies,

of

the walls and roof of which were built of large

unmortared slabs. A circular mound or cairn of stones covers the tomb and a kerb of massive slabs, laid with their long edges touching, base of the cairn and acts as a retaining feature.

surrounds the

Surrounding the mound,

but situated from 7-17 m. outside it, is a circle of tall widely spaced standing stones. From the astronomical point of view, one of the most interesting of Newgrange is the so called entrance in Fig.

'roof-box'

features

(which can be seen above the main

1) which rests on the front part of the passage roof at

about 2.4 m. back from the entrance.

This roof-box is 90 cm. high,

I m.

wide and 1.2 m. in depth and it is situated above a small gap, 20-25 cm. wide, between the first two roof slabs of the passage. Professor M.J. O'Ceallaigh,

The archaeologist

who has been associated over several years with

the reconstruction of Newgrange,

found at sunrise on the mid-winter solstice

of December 21, 1969 that, for about 17 minutes,

direct sunlight entered the

monument through the slit below the roof-box and penetrated down the passage to illuminate the central chamber.

Mr. Jon Patrick has since made a survey to determine

if such a solstice-

related phenomenon could have occurred when the tomb was newly built, concluded from his measurements

and he

that the sun's rays would have always

entered directly into the chamber if its declination lay between -22 ° 58' and -23 ° 53', a range covering the angle of obliquity of the ecliptic. suggests that a geometrical/astronomical of the monument,

This

design was used to fix the position

although it must be remembered that the probability that a

randomly oriented structure would align with the solstitial position as Newgrange does is about one in ten or fifteen.

It should also be noted that

the south-east is a favoured aspect with the builders of passage graves. General observations made at Newgrange

show that direct sunlight penetrates

to the inner chamber for about one week before and one week after December 21. This suggests that the function of the alignment, deliberate and determined astronomically, of precise calendar observations.

if it was indeed

was not concerned with the making

Thus, a surmise consistent with the

available evidence is that the underlying purpose may have been ritualistic or symbolic rather than scientific

although an element of astronomical

awareness was very probably also involved. Evidence

suggesting the existence of an interest in lunar cycles at the

Boyne Valley site has been pointed out by Brennan in a recent book in which he draws attention to special patterns on a kerb stone located in the southwest section of Knowth,

another passage grave in the same general complex.

On this stone, which is depicted in Fig. 2, there is a sequence of twentynine symbols, spiral,

one of which,

immediately to the left of and above the large

is interpreted by Brennan to represent the first appearance of the

Astronomy in Ireland

FIG 1

The Passage Grave at Newgrange, River Boyne.

3

:

;

FIG 2

':" " ' " ~:" "' : :"

.'~',~

:~

-~

~,...., ~

r';:-,

d:'~

r "-~

.:

~t,

.

-

The

~

~

,,..)

,, ,, ,,

.........~.~..._~

.

Calendar

.

.

Stone

.,.~¢..~'~:

....!

((i(,~.;~.,))/) ;~i:.,t,,, ["4.~

~-'~[) D 7 3 D ~ ~ , ~ ,

,,

The "Calendar Stone" found at Knowth, River Boyne.

,~,.~

f

.,'

!

o

I p~

FIG 3

The Stone Circle at

Drcmbeg,

Near Glandore,

Co.

Cork.

r~

o ,<

r~

Astronomy in Ireland

7

crescent of the waxing moon in the western sky. The crescent form is repeated, without significant

change,

for the equivalent

the moon begins to become much brighter.

of eight to nine days, when

Positions

eleven and twelve are

suggested to represent the moon as it become higher in the evening sky and the crescent fourteen, which,

shape is depicted as changed to an oval. Again, positions

fifteen and sixteen are deemed to represent the period of full moon

by day seventeen,

From this point, twenty-seven,

decreases until it is smallest on day

when the last glimpse of the crescent is visible

eastern horizon. 'hidden'

is shown waning and resuming its crescent shape.

it progressively Finally,

positions

twenty-eight

on the

and twenty-nine

are shown

behind the spiral symbol.

This interpretation

of the carvings

(a) one has the cyclic arrangement

appears to be quite plausible

shape and back again and (c) the number of individual twenty-nine.

Indeed,

if the carvings

earliest that can be identified,

since

(b) transition from a crescent to a disk symbols used is

do represent a lunar calendar,

without serious ambiguity,

it is the

in either

Ireland or Great Britain. Turning now to stone circles, astronomical recently,

it may be noted that belief in their

purpose has been strong since the nineteenth

Professor Alexander Thom, using a wealth of material

in particular

at megalithic

circles were observatories

sites in England,

gathered

for precise

objects,

and accurate

notably the sun and

He further argued that the circles were set out by people who used a

standard unit of length equivalent megalithic

yard,

pre-determined criticism

to 2.72 feet, generally known as the

and that the circles were constructed

geometric

shapes.

to sophisticated

This viewpoint has attracted considerable

as well as some support in England and, at the present time, the

case for the national In Ireland,

distribution

of the megalithic

Barber has made a computerized

analysis

yard remains unproven. of thirty stone circles

in the south west of the country and concluded that, rate,

Most

has argued that British

used by their builders

studies of the motions of certain celestial moon.

century.

there is no evidence

of the use by the builders

for these rings at any of a megalithic

Not all of the Irish stone circles are of the same pattern, of the south-west

group is a class characterized

but typical

by free-standing

which vary in number from five to fifteen- with a correspondingly of diameters. so-called

A feature of these structures

'recumbent

stone',

is the incorporation

a portal,

opposite

uprights wide range in them of

that is a slab set in the ground on its side

rather than on its end and having an upper straight horizontal Diametrically

yard.

edge.

to the recumbent is a pair of matched stones forming

which is usually higher than the other uprights.

Fig. 3 shows a

good example of such a circle which is located at Drombeg near Glandore, Co. Cork. The tall stones to the left of the picture are the portals, opposite stones.

to this is the recumbent,

and

which is partly obscured by the other

8

S.M.P. McKenna-Lawlor

Again Barber,

in his study of thirty south-western Irish circles, having

defined the main axis to be a line passing between the portals and ove~ the central point of the recumbent,

went on to examine the orientation of the

axes of these particular structures relative to the rising ans setting positions of a number of astronomical objects.

Taking into account the

limits of accuracy with which the main axis is in fact identifiable,

he

demonstrated that seventeen sites contained orientations on the Sun, Moon and Venus;

ten had possible stellar alignments and three others were

apparently unrelated to a celestial event. Barber did not however conclude from his observations that the circles were observatories in the modern sense of the word. Rather, he inclined to the view that the stimulus which drove the builders to create these structures in the first place,

also impelled them to include in their design an

awareness of the cycles of some few celestial objects.

In this, he

differentiates between the observation that astronomical

sighting lines were

associated with some megalithic monuments and the speculation that such alignments were used for a specifically astronomical purpose. interpreting the evidence is indeed very necessary, statistically,

Caution in

not least because,

the odds are in favour of a good celestial sighting occurring

fortuitously in almost any circle.

Indeed, with so many possible celestial

targets to choose from, to discover no correlation would,

in itself, be

rather improbable. If next we seek to find out something about astronomy in pre-Christian and early Christian Ireland from literary sources, we find that the earliest records available refer specifically to the Celts.

It is a matter of some

scholarly debate as to when Celtic culture first came to Ireland, for the present purpose,

but,

it is sufficient to indicate a very general date

in the late Bronze Age, of the order of 600 B.C. The written sources may be, for convenience,

divided into two distinct categories,

namely

(a) the

testimony of Greek and Roman authors concerning the characteristics

of

Celtic society and (b) Irish vernacular sources. The classical documents to conditions

suffer the disadvantage

that they refer in general

in restricted areas of the European continent and Britain

rather than to the whole Celtic world, second-hand and unreliable.

and frequently the accounts are

Within them however we find evidence of a high-

ranking class of Celtic learned men who are referred to as Druids.

Strabo

mentions particularly the druidical knowledge of moral philosophy and natural science while Caesar, of the Druids movements,

in his account of the conquest of Gaul,

says

"They hold long discussions about the heavenly bodies and their

the size of the universe and of the earth,

constitution of the world and the power and properties instruct the young men in all these subjects."

the physical of the Gods and they

From Caesar we also know

that the Celts counted by nights and not days and that in reckoning birthdays, the new moon and the new year their unit of reckoning was night followed by day. Pliny also ascribes this form of time measuring

Astronomy in Ireland

specifically

9

to the Druids saying "It is by the moon that they measure

their

months and years and also their ages of 30 years." Non-literary

evidence

of the Celtic approach to measuring extended periods

of time is provided by a bronze plate unearthed engraved

the so-called Coligny Calendar.

in France,

This is divided into half months,

it reckons by nights and marks lucky and unlucky days. construction

it represents

on which is

In basic

an adjustment of the lunar to the solar year by a

process known as intercalation.

A period of 12 lunar months constitutes

a lunar year and, is a lunar month is counted as 29~ days, the lunar year contains

354 days.

It is thus 11¼ days shorter than the solar year so that

the cycle of lunar years would, with time, become progressively and more out of step with the seasons. inserting an additional

Intercalation

more

is the process

line with the solar year and, in the case of the Coligny Calendar, are two intercalations

of

day or days in a calendar in order to bring it into there

of 30 days each, one at the beginning and one in the

middle of the five-year period covered. If now we seek for information sources,

concerning Celtic society in Irish vernacular

we enter a world which is totally different texts.

etymology

of the word appears to be different and there is a special

emphasis magic.

Here,

from that of the

classical

on associating

although for example Druids are referred to, the these personages with powers of divination

and with

The documents however identify certain orders of learned men,

including in particular

the File, a word which,

be applied particularly

to poets,

although it later came to

referred in the early period to a class

whose members had wider functions.

It is in this context of particular

interest to quote here part of a well-known

incantation

ascribed,

from long

before the Christian era, to the File Amergin Gluingel which refers specifically

to his knowledge

of lunar and solar cycles.

"Who spreads light in the gathering on the mountain? Who foretells the ages of the moon? Who teaches the spot where the sun rests? Who, if it be not I" It is clear from the text that he was also concerned with transmitting astronomical importance

knowledge

to others,

to the well-being

The main divisions

of a calendar-dependent

Samrad

(Summer),

Fogmar

from folklore

that the solstices

(Winter) and they

May, August and November respectively.

special festivities were celebrated,

It may also be a common practice stars since,

society.

life. These divisions were Errach

(Autumn) and Gemred

began on the first days of February, At these times,

agricultural

of the Celtic year are indeed known to have been related

to the annual round of agricultural (Spring),

his

an activity no doubt of special

but there is evidence

and equinoxes were also observed. in ancient Ireland to tell time by the

in a story of the Ulidian cycle,

described as bidding his charioteer give warning when midnight arrives."

the hero Cuchulain is

to "go out and watch the stars and

I0

S.M.P. McKenna-Lawlor

There is some question as to whether the file existed from earliest times side by side with the Druids, represented

an evolution

Professor Myles Dillon, with Christianity a long tradition

whom they survived,

of the Druidic in discussing

orders.

the coming of Latin learning to Ireland

in the fifth century,

remarked that the Irish had already

of native learning which had grown up in the Druidic

schools and which were preserved

by the File through oral transmission.

is of interest to us here however is that, society by Christianity, internally

stratified

orders of wisdom. other subjects, Interest,

or whether they rather

In this connection,

ecclesiastical

according

to

In this system,

within a monastic

schools were set up which were

the so-called professors

to master arithmetic setting,

seven grades or seven

of the fifth grade had, among

and astronomy. in the cycles of the sun and moon had,

in fact, a direct bearing on one of the most vexed questions early Church,

namely the setting of the date of Easter.

was the dependence

What

following the overthrow of pagan

of the ecclesiastical

to trouble

the

Basic to the problem

calendar on solar and lunar cycles.

The year of the sun is now known to be 365.2422 days while a lunar month is 29.3506 days. Dividing one period by the other we obtain 12.3683 and the decimal

fraction excess of lunar months

in a solar year can be expressed by

the common fractions 3/8 = 0.3750; To reconcile

4/11 = 0.3636;

the lunar and solar years,

lunar months every eight years,

7/19 = 0.3684;

calendar makers could insert three

four lunar months every eleven years,

lunar months every nineteen years and thirty-one four years,

and in fact all of these solutions

were tried experimentally adoption of a particular be made,

of the cycle considered,

lunar months every eighty-

a number of arbitrary

such as what might be appropriately

seven

as well as a number of others

by the Christian calendar makers. cycle,

31/84 = 0.3690

Given the

decisions had then to

defined as the starting year

where should extra days be introduced

into the

calendar and what were the limits within which Easter Sunday could fall. In Ireland, celebrated

from the earliest days of Christian observance,

on that Sunday which occurred between the fourteenth

day after the first full moon after the twenty-fifth traditional

date of the Crucifixion.

that pertaining

in other countries,

as the Easter Controversy position,

This practice,

constructing

and twentieth

of March, which was the which was different

from

provoked a profound dispute now known

and the Irish monks,

as a result took a particular

who were in a defensive

interest in the mechanism

of

Easter tables within the context of the special difficulties

of astronomical

time reckoning and the requirements

By the year 636, normal Church procedure conforming monasteries celebrated

Easter was

of dogma.

was accepted by hitherto non-

in the south of Ireland,

thus causing Easter to be

on the first Sunday after the first full moon after the Spring

equinox of March 21. Thereafter, in local practice

possibly to avoid any further divergence

within the Church,

the Venerable

Bede of England produced

Astronomy in Ireland

II

a treatise which became a standard work for computists

on the problems

of time reckoning and their handling. Bede's calendric

methods were not based on astronomical

even on a consideration

rather founded purely on arithmetic view them now as astronomy-related own right.

observations

of the geometry of solar and lunar orbits.

The Easter Controversy

however three particular

benefits

methods

and parameters,

or

They were

so we can

rather than being astronomical

in their

and the way it was handled conferred on astronomy which are of relevance

to us

here. Firstly,

the business

of collections

of computing Easter tables gave rise to the assembling

of manuscripts,

now called computi.

included only the Easter tables themselves, and verses for memorising themselves

works on arithmetic,

collections scientific

currently provide

rules,

astronomy,

but later they attracted to

chemistry and medicine.

a very useful source of information

life of the period and many examples

particularly Secondly,

computistical

in libraries

These at first typically

lists of associated calculations

of Irish computi exist,

on the continent.

the recording of Easter dates with related material

the popular medieval

activity of compiling Annals.

to celestial

events such as eclipses

comets which are of considerable Thirdly,

the professional

led quite naturally

scientific

and they contain many

and the apparitions

of the Greek philosophers

approach to celestial motions. Irish monks and they,

In this way, they became exposed and in particular

From the fragments

Geometer,

to the Helenistic

that remain from this

model was generally adopted by the

in turn, taught it to their students both at home and

in those parts of the continent to which their wandering gives fascinating

astronomers

of

interest to-day.

to their making an in-depth study of such books on

period we can deduce that the Ptolemaic

literature

Irish

interest of the monks in solar and lunar cycles

astronomy as came their way from overseas. to the writings

gave rise to

The voluminous

Annals are of course very well known internationally references

These about the

glimpses of the activities

and we read for example of Virgilius,

took them. The of these monk

also known as Fergil the

who arrived in France in about the year A.D. 741 and got into

considerable

trouble with the ecclesiastical

following Plato,

authorities

that the earth is spherical,

under the earth and that there are inhabitants was apparently

initially

existed another world, Adam and therefore

through teaching,

and the sun and moon pass on the earth's other side. It

supposed that Virgilius was postulating

that there

populated by races of men who were not the sons of

not redeemed by Christ, who had a different

sun and

moon to shine upon them. This certainly was not the teaching of Virgilius and he apparently words,

succeeded in satisfactoril

explaining

the meaning of his

since he was later raised to the See of Salzburg.

In 811 the Irish monk Dungal in reply to a request from the Emperor

12

S.M.P. McKenna-Lawlor

Charlemagne

that he would explain why two solar eclipses had occurred

the previous

year,

sent a lengthy epistle

an account of the celestial

to the Emperor in which,

sphere according to the Ptolemaic

went on to explain the mechanism by which eclipses

in

following

system,

he

of the sun and moon

occur. Again,

in the ninth century,

Dicuil the Geographer

dedicated

an astronomical

work in prose and verse to Louis the Pious, while John Scotus Eurigana produced

a philosophical

geoheliocentric

work in which he discussed

the so-called Greek

system according to which Venus and Mercury move in circles

around the sun while the sun moves around the earth. In the first poem of the Saltair na Rann written in Ireland about A.D. the earth is stated to be like an apple,

truly round,

1000,

and we are told that th~

sky is around the earth as the shell is around the egg. The signs of the zodiac with their names in order are given as well as information the sun, moon and planets

every intelligent person should know, of the moon,

'early Latin astronomy'

significant

connection

of detailed

source material

advancement

in stellar knowledge

Christendom.

In Ireland itself,

between astronomy

instrumentation,

was made during this period in Western

of two centuries

in about A.D.

of sacking and plundering

and, in consequence,

a sustained climate of

The coming of the Normans in 1169 produced

disruption in the intellectual closing of the monasteries

any

no significant

the arrival of the Vikings

of Irish schools and monasteries activity.

could not however provide

and theory and, in the absence

and developed

800 signalled the commencement

overseas

the age

the day of the week and the

festivals.

What may be called

scholarship

the day of the solar month,

the time of the flow of the tide,

chief saints'

concerning

and there follows a statement of five things which

further

life of the country and, following

under Henry Vl11, many people

the

sent their sons

for education.

This practice prompted Elizabeth undesirable,

I, who considered

to grant a charter for the founding of a College

Trinity College in Dublin - which would promote learning.

such practice

Within this new institution

1683 within which scientific

a Philosophical

who was especially

not only published

observations

and books concerning physical

This activity formed a prelude period for Irish astronomy

and its Secretary

interested

in astronomy

several papers in the Transactions

Royal Society concerning his astronomical number of articles

- the present

civility and

Society was set up in

topics could be discussed,

and founder William Molyneux, and telescopes,

religion,

politically

A previous

article

"Astronomy

in Ireland from 1780" describes

in Vistas in Astronomy

oustanding

observatories

of the eighteenth

by the present author,

founded throughout

a

optics.

to what was to become a particularly

from about the middle

of the

but also produced

brilliant century.

entitled

some nine of the more the country following this date,

Astronomy in Ireland

13

and reference is also made to the important role played by the internationally known Irish telescope makers Thomas and Howard Grubb in supplying many of these observatories with equipment of the highest quality.

ACKNOWLEDGEMENT My best thanks are due to M. Brennan for permission to reproduce Figure 2 a representation of the Knowth 'calendar stone'.

REFERENCES Barber, J. (1973) Cumann Seandalaiochta is Stair Chiarrai (Journal of the Kerr Archaeological and Historical Society) No. 6, pp. 26-39. Brennan, M. (1980) The Boyne Valley Vision (The Dolmen Press, Portlaoise) McKenna, S.M.P. (1968) Astronomy in Ireland from 1780. Vistas in Astronomy, Vol. 9, PP. 283-296. (Pergamon Press Oxford: ed. A. Beer) O'Kelly, C. (1978) Illustrated Guide to Newgrange and the other Boyne Monuments (Ardnalee, Cork). Patrick, J. (1974)

Nature Vol. 249, pp. 517-519.

Thom, A. (1966) Megalithic Astronomy: Indications in Standing Stones. Vistas in Astronomy, Vol. 7, pp. 1-58 (Pergamon Press Oxford: ed. A. Beer.)