Megalithic Astronomy - with emphasis on Great Britainfverbunt/iac2011/hlmeg.pdf · 2011-04-26 · Example 1: Stonehenge (Heggie p.148) Stonehenge I: 3000 B.C. The ﬁrst version of

Megalithic Astronomywith emphasis on Great Britain

Frank Verbunt

Astronomical Institute, University of Utrecht, Netherlands

April 26, 2011

Frank Verbunt (Astronomical Institute Utrecht) Megalithic Astronomy April 26, 2011 1 / 29

Outline

1 Introductionthe megalithic monumentsarchaeoastronomy

2 Sightlines and directions

3 ExamplesStonehengeresults by Thom on multi-site analysis

4 New research by Rugglesthe Hebridesthe GrampiansCork-Kerry

5 The need for restraint and critical attitude

6 Conclusions


the megalithic civilisation

chronology(calibrated) C-14 dates:Stonehenge much older thanGreek Bronze age!

farming enhanced in MiddleEast: use crop to feed cattle,use cattle dung to grow crop

arrives in southern Europe±5500 B.C.

arrives in Great Britain±4100 B.C.

(agricultural surplus? leadsto?) large-stone monuments

Mykenae & Stonehenge


archaeoastronomy1740 Stukeley: main axisStonehenge points tonorth-most sunrise

1905 Lockyer datesStonehenge on this direction

1966 Hawkins: Stonehengedecoded as astronomicalobservatory

1966 Hoyle: Stonehenge aseclipse predictor

1967 Thom writes surveyMegalithic sites in Britain

criticism1966 Atkinson: Moonshineon Stonehenge: takeaccount of archaeologicalknowledge

1981 Heggie MegalihicScience: do statisticscorrectly

1999 Ruggles Astronomy inPrehistoric Britain andIreland: new, correct studies


Defining sightlines

Sightlines1 line connecting ≥ 2 menhirs2 symmetry axis of ring; or line from

center ring to stone in ring3 line from monument (ring, grave,

menhir group) to distant stone4 grave with corridor5 lines between monuments (rings,

graves, menhir groups)6 line from monument (ring, grave,

menhir group) to natural sight(island, mountain)

7 other (very rare)

also take into account:height of horizon andatmospheric refraction

accuracy of sightline (8◦

at Stonehenge, 1′ forfaraway natural foresight)

is the sightline visible?(intermediate hills orforest)

how many lines can onedefine?

have stones beenmoved?


Interesting directions

The Sunmost northern sunset orsunrise (midsummer)

sunset or sunrise at equinox

most southern sunset orsunrise (midwinter)

The MoonThe orbit of the Moon makes anangle of 5◦ with the ecliptic⇒: theMoon has extreme location of risingor setting at locations

δ(Moon) = δ(Sun)+5◦

δ(Moon) = δ(Sun)−5◦

3 × 2 = 6 special directions for Sun. Add 2 × 6 = 12 for Moon to get totalof 18 directions. Note: all these lines are defined by declination δ of Sun orMoon, which convert to different azimut in different locations⇒ convertmeasured azimuth at horizon to declination before comparing locations.


Example 1: Stonehenge (Heggie p.148)

Stonehenge I: ±3000 B.C. The first version of Stonehenge(Stonehenge I, ±3000 B.C.)consisted of a ring of 57 holes, and abank and ditch just outside it. Nearan opening in the latter, two stoneswere standing inside the bank, andfour some distance out. Togetherwith the center of the circle thesedefine the main axis of Stonehenge.Next to the four outside stones, oneor possibly two larger stones hadalso been erected; one of these isthe Heel Stone.


Example 1: Stonehenge (Heggie p.148)

Hawkins 1966: Stonehenge Iassumed date: 1500 BC(correct: 3000 BC; notimportant for Sun or Moon)

18 interesting directions:set/rise Sun/Moon; accuracy±2◦ ⇒ probability 1 trial is:18 × 4/360 = 0.2

50 directions defined bystones of which 24 hits:probability 24 hits in 50 trialswith p = 0.2 (Poisson):0.00006

Atkinson 1966correct probability 24 hits is0.000006

but should be for ≥ 24 lines, andis 0.000008

there are in fact 111 lines andprobability of ≥ 24 hits is 0.37⇒not significant

Poisson statistics done simply111 lines, probability 0.2⇒ expectednumber of hits is 22 ±

√22 (1σ)⇒

24 hits is within 1 σ of expectation


Example 2: Stonehenge II (Heggie p.198)

Stonehenge II: ±2500 B.C. A later version of Stonehenge(Stonehenge II, ±2500 B.C.) addedfour large stones – the Stationstones – to the ring, and – accordingto Atkinson, but cast into doubt bylater research – shifted the main axissomewhat, by replacing the twostones just inside the bank. If thecentral ring and horseshoe made oflarge stones were put into location atthe same time, they would haveblocked the view between the stationstones.


Example 2: Stonehenge II (Heggie p.198; updated)

Example: p.198 Stonehenge Station Stones rectanglesides, diagonal: 4 directions

1 parallel main axis: 3 new

2 point to interestingdirections

6 interesting directionsp = 6 × 3.6/180 = 0.12

3 trials P(1)=0.25, P(2)=0.04⇒ 1 intentional, 1 accidental

PB(k , n, p) =

(nk

)pk (1 − p)n−k


Example 3: Thom 1954 on many sites (Heggie p.152)

declination of Sunδ� = ε,−ε at solstitia

between 3000 B.C. and 1500B.C. ε ranged from 24◦03′ to23◦52′.

allow for 15′ radius Sun:range becomes 24◦19′ to23◦36′ which is 43′

sightline selectiontake all lines in range23 < |δ| < 25, i.e. range of 120′

7 lines found, all in acceptedrange for Sun

probabiblity hit with one trial:43/120'0.3

probability 7 hits in 7 trials is0.37 < 0.001⇒: direction tosolstitia are significant

separated by 30′ ⇒ upper andlower limb of Sun were used


Example 4: Thom 1967 on many sites (Ruggles p.56)

Survey of British Islandsselect lines in lunar directions,determine difference ∆δ tonearest lunar direction

for each line, plot Gaussianwith unit surface, center on∆δ, and width of uncertainty in∆δ

add all Gaussians: left graphin Figure. top: allmeasurements, lower: onlyaccurate measurements

separation 2 peaks ' lunardiameter: rim of Moonobserved

Critique Ruggles (1999)remove lines from dubious(non-megalithic) sites: result ismiddle plot

re-measure lines: righthand-side plot

conclusion: no evidence fordouble peak


Example 5: Thom 1955 (Heggie p.159)

solstitiaselect lines from center circleto outliers: 17 lines on 9 sites

select alignments: 21 lineson 14 sites

result: significant excess tosolstitia and equinoxes

Critique Heggie:

excess due to solstitia only

not all acceptable lines werecounted

treatment of 2 directions inone alignment is not clear

starsassumed date 2100 B.C.

22 hits, probability < 0.001

Critique Heggie:

many lines of low quality

of 9 high-quality lines 6 are ondubious sites; nonetheless 5pointed to Rigel

number of lines critical indetermining probability


New research by Ruggles

Areas of new research How to do it rightTo avoid biases in pre-selecting linesbefore statistics is done, (which ismuch evident in earlier work byThom and Hawkins), Ruggles andcolleagues decided to make a large,fully unbiased survey of megalithicmonuments in the Hebrides.


New research by Ruggles

The Hebrides (Ruggles p.91)Select lines in order of quality

1 row of three or morestanding stones

2 row of three or morestanding/lying stones

3 two stones with third stonelying

4 two stones, one lying5 flat side of standing slab6 flat face of lying slab

On each site, keep only lines ofthe highest quality class.

ResultsThis leads to 296 directions withallowed ranges. The distribution ofthe directions is shown in the Figure(histogram) and compared withexpectation according to chance(smooth line, found by arbitrarilyselecting directions from the allowedranges).


Results by Ruggles et al. for the Hebrides

There are significant excesses near the lunar directions at rise in thesouthern maximum (−ε − 5◦ = −28◦), and some beyond. In the northerndirection the significant excess is at too high declinations.


Results by Ruggles et al. for the Hebrides

The HebridesIf we plot the directions interms of azimuth, we see thatmost directions are to thenorthern and southernquadrants. Left, all lines areshown; right, the ones fromthe Outer Hebrides (the twoislands top left in the areaindicated on p.15) have beenremoved. This looks moreconvincing, but at the cost ofsome arbitrariness inselection...

ConclusionsMaybe the sites were aligned on themost southern rise/setting of the Moon.Maybe they were aligned roughly in asouthern/northern direction.


New research in the Grampians (Ruggles p.91)

Ruggles & Burl (1985) measured directions in stone circles, in which oneof the stones in the circle lies flat, with two standing stones next to it. Thefirst figure shows the directions a) from the circle center across the flatstone b) perpendicular to the long axis of the flat stone; both measured inthe Grampians, and showing a preference for declinations near |δ| = 30.For comparison similar directions measured in Cork-Kerry in Ireland areshown in c); these have no preferred direction.The second figure shows directions a) from the same circles toconspicuous hilltops b) from the circle center across a cupmark on the flatstone; c) hilltops in the Irish comparison sample. −30◦ is further souththan the Sun comes; which may mean that the directions are to the mostsouthern Moon.It is remarkable that the people in the Grampians and in Cork-Kerry madevery similar stones, where those in the Grampians were aimed for theMoon, and those in Ireland randomly directed.


the Grampians: direction across flat stone


the Grampians: from circle to faraway hilltop


New research in Cork-Kerry (Ruggles p.102)

Ruggles also investigated the rows of stones in Cork-Kerry. He finds apreference for directions |δ| ∼ 30◦; since the Sun at the time was atδ ' 24◦, this suggests that the Moon, rather than the Sun was the target ofthe alignment (|δ|(Moon)= |δ|(Sun)+5◦ at the extremes). In some cases therow of stones points in one direction; in some case two directions arefeasible. The latter cases are included in the lowest graph.

Rows of stones may also point to hilltops in the distance. The directionsfound in this way, again for Cork-Kerry, are shown in the Figure. Forcomparison, the lowest graph shows similar directions for rows and hills inwestern Scotland. It appears to me that the southern directions arecompatible with being purely solar.


Cork-Kerry: rows of stones


Cork-Kerry: rows pointing to distant hilltop


The need for restraint and critical attitude

Be criticalMany publications still appearthat claim alignments that arenot substantiated by a validstatistical analysis. Suchalignments are not believable.In particular studies of sitesoutside Europe appear to bestill in the pre-Heggie era ofarchaeoastronomy, and proneto over-enthusiasm.

ExamplesThe reader may test her/his criticalacumen on

The Orion mystery by Dauval &Gilbert (1994) claims that thepyramids of Gizeh are an image ofthe Orion constelllation

Sterne und Weltraum 421, 34(2003) claims that the Nebra disk isa map of the sky

National Geographic May 2004claims an alignation of Mayabuildings in Guatemala with ηDraconis


Assorted garbage

National Geographic May 2004 Sterne und Weltraum December 2003alignment on η Draconis. . . sky map with Pleiades. . .


Conclusions on Megalithic Astronomy

Megalithic structures occasionally show preferred directions, which may beinterpreted as astronomical. Early research (before 1980) suffered fromflaws in the statistical treatment, but was important in developing aninterest in the field. Since the 1980s better defined research has beendone, and from this it follows

there are significant directions towards most northern and southernsunsets/sunrises (the solstitia)

there may be significant directions towards the most northern andsouthern moonrise/moonset; alternatively they could be towards thesun, if the builders did not strife for large accuracy, but merely for arough indication of direction.

there are no significant directions towards stars

Significant here means: it can be shown from a statistical analysis that thefrequent occurrence of the direction is unlikely to be due to chance.


Conclusions on Megalithic Astronomy

It should be noted that astronomical explanations are not the onlypossibility. An example of very different interpretations is the location ofmegalithic sites on the north side of the island Mull. The sites are often onlocations on the lines which separate the areas where one can see themountain Ben More from those where one cannot (Ruggles, p.115).

It should be noted that statistical analysis has its limits. That we cannotprove something statistically doesn’t prove that it is not the case; inparticular, single sites cannot be analysed in a statistical way. Forexample, if three henges are roughly in positions looking like the belt ofOrion, this may or may not be what the builder intended – we cannot know.


Literature

Advised readingDouglas Heggie, MegalithicScience, Ancient mathematicsand Astronomy in NorthwestEurope, 1981, Thames & Hudson.History of topic, and items 1-3above. An absolute must for anystudent of megalithic astronomy.

and:Clive Ruggles, Astronomy inPrehistoric Britain and Ireland, 1999,Yale University press. Three parts:

as Heggie, less concise

new research (item 4 of Outline)

synthesis with archeology

Well illustrated; rather verbose inplaces (esp. 3rd part).


Exam problem 1: precession and Stonehenge

Sunrise at StonehengeStonehenge is at 51.178◦N.

1 Compute the most northernazimuth of sunrise atStonehenge in 2000 AD

2 with precession at constantobliquity ε, compute the mostnorthern azimuth of sunriseat Stonehenge in the year3000 B.C.

3 with full precession computethe most northern azimuth ofsunrise at Stonehenge in theyear 3000 B.C.

Stonehenge ±3000 B.C.4 is it possible to date

Stonehenge from its mainaxis? Explain yourreasoning.


Documents

Megalithic Astronomy - with emphasis on Great Britainfverbunt/iac2011/hlmeg.pdf · 2011-04-26 · Example 1: Stonehenge (Heggie p.148) Stonehenge I: 3000 B.C. The ﬁrst version of