2007.12.22
 I
need accurate GPS readings for Avebury's monumental
landscape. A recent inquiry led to assessing geospatial ordering of
several Neolithic long barrows on the British Isle. The two largest
are both near Avebury. West Kennet Long Barrow and East Kennet
Long Barrow are 330350
feet long and up to 120 feet wide and 20 feet high. The arc
distance between their centerpoints presents the value of days
per lunar orbit, an astronomical constant.
The Avebury to Silbury Hill arc (avebusilhi =
0.013070°) is nearly
the same length as that between these largest of long barrows (wkelbekelb
= 0.013178°). The slight difference
between the two arcs is 12 m. Both arcs present astronomical
constants, days per lunar orbit and days per lunar anomalistic period.
The anomalistic period is 27.55455 days and sidereal orbit
was 27.32167 days. Dividing circumference (cir) by these constants
times 1,000 equals the monument arcs, i.e. cir / 27,321.67
= 0.013176°.
Geodesy

Astronomy

arc

length

value

constant

wkelbekelb

0.013178° = cir / 27,319

27.32167 days

Sidereal orbit (s7)

avebusilhi

0.013070° = cir / 27,545

27.55455 days

Anomalistic period (s5)

The following actual distances and
astronomy equivalent arcs provide
an idea of the scale and the comparison illustrates the accuracy.
The submeter inaccuracy is less than the precision expected of the
coordinates.
Actual distance

Astronomy equivalent

arc

length

value

constant

wkelbekelb

0.013178° = 1,465.3 m

1,465.1 m

cir / 1,000 s7

avebusilhi

0.013070° = 1,453.3 m

1,452.8 m

cir/ 1,000 s5

Consideration
of accuracy of methods—basically "When
is close close enough?"—is very distinct from considering
builder intent. Precise does not by
itself assure a positive answer to intentionality. If the builders
intended to monumentalize the lunar constant with the arc length,
further evidence is needed to support this hypothetical.
I've turned to examining the monument
geometry further, wondering, "Do other aspects of this landscape
geometry also infer intentional arrangment?" The Kennet barrows
align on Longstone Long Barrow, a position less precisely discernable
in Google Earth (GE). With that caveat, the geometry these three points
form seems intentional. More on this below, after short descriptions
of the sites collected from several sources. The Avebury Arcs GE file
provides further visual description.
Avebury Arcs 
Placemarks in a Google Earth File
http://www.jqjacobs.net/archaeo/sites/avebury_arcs.kmz
The Sites
East
Kennet Long Barrow. A Late Neolithic chambered
long barrow dating from c. 3500 BC, a substantial earthwork orientated
northwest/southeast, broadly rectangular, 106m long by 50m wide
and c8m high,
largest long barrow in the British Isles, with sarsen stones at
the southern end. Silbury
Hill and surrounding countryside views are magnificent in all directions.
Excavated in the 19th century, flanking ditches quarried during
construction parallel to the southwest and northeast sides survive
to a width of c5m as a low earthwork on the northeast.
West Kennet
Long Barrow. A
Late Neolithic chambered long barrow dating from c. 3700 BC, 340 feet
long, 75 feet wide, oriented EW, with eastern entrance 12 feet high
standing stones. Passage extends 40 feet to five sarsen stone
chambers.
The trapezoidal mound is formed with a sarsen
boulder core and chalk rubble capping from flanking quarry ditches. The elaborate
megalithic structure on
the east end of the mound includes an axial
passage with five chambers. The
massive sarsen facade, aligned northsouth, has a
semicircular forecourt.
Long Stones Long Barrow. A Neolithic long barrow dating from c.40003500 BC, 225 feet long, 120 feet
wide, 15 feet high. Located due south of Windmill Hill. Windmill Hill
dates from c. 3,500 BC.
Silbury Hill Mound. Covering
over 5 acres, the massive flat top mound standing
130 feet high was built starting between 2445
and 2190 BC, per
radiocarbon dating. Silbury Hill is
the largest prehistoric manmade mound in Europe. English Heritage reports 30 metres
high and 160 metres wide,
roughly 4 million hours of work, and 500,000 tonnes of
mostly chalk from surrounding terraces and
ditches.
Windmill Hill Henge. Dating
to near 3500 BCE, the Neolithic causewayed enclosure is one of the oldest
of the Avebury monuments. The typesite and
largest 'causewayed camp' (a henge type) and typesite for 'Windmill
Hill culture' pottery consists of three concentric circular/elliptical
banks and ditches 365m in outer diameter.
Avebury is
described in a previous Neolithic
Monuments web log.
Monument 
Code

Latitude

Longitude

Windmill Hill 
winhi

51.442086

1.876791

Avebury 
avebu

51.428609

1.854072

Longstones Cove Standing Stone A 
lcssa

51.422689

1.873444

Long Stones Long Barrow 
lstlb

51.421207

1.876271

Silbury Hill 
silhi

51.415710

1.857449

West Kennet Long Barrow 
wkelb

51.408589

1.850987

East Kennet Long Barrow 
ekelb

51.400583

1.834208

Additional Long Barrow Coordinates: long_barrows.xls  long_barrows.rtf
Applications,
Coordinates, Code, Articles:
http://www.jqjacobs.net/astro/archaeogeodesy.html
2007.12.28
 Winter Solstice and Long Barrows ... the
solstice has passed, but I'm not passing over the solstice aspect of
this topic. I noted several other angles matching the arc distance from
Avebury to Silbury Hill, both the winter solstice angle and the bearing
to Mont Blanc. In
the previous post, I discussed
summer solstice sunset at Avebury aligning to Newgrange when obliquity
equaled 24 degrees (±2,758 BCE). In opposition
is winter solstice sunrise. These two major site
concentrations, at Newgrange and Avebury, align
on Mont Blanc—the highest point in Western Europe. Coincidentally,
at the Avebury concentration, winter solstice azimuth is the
same as the Mont Blanc bearing.
Winter solstice
sunrise at the Silbury Hill to East Kennet latitudes ranged from
130.72° to
130.71° E. of N (using GeoAstro formulated by Victor Reijs).
The bearings to the presentday Mont Blanc summit range between 130.74° and
130.71°.
Air temperature variation alters the solstice angle more than this
degree of swing. The solstice angle changes near 0.02° per century
due to the change in obliquity, in earth's rotation axis angle. The
bearing to the mountain is relatively fixed, albeit secular polar
motion has altered latitudes and polar azimuth slightly given the
age of these monuments. Ice, of course, changes on the mountain.
One tenthousandth
of the solstice angle equals the AveburySilbury Hill arc distance
(0.01307°) even
with the slight variations in angles below given the
fifth decimal of a degree of arc (0.00001°) is
a mere yard in length.
Monument Arcs

Astronomy

sites

distance

bearing

solstice 2,758 BC

avebusilhi

0.013070°


avebu = 130.736°

wkelbekelb

0.013178°


ekelb =
130.706°

silhimonbl


130.7358

silhi = 130.722°

wkelbmonbl


130.7212

wkelb = 130.714°

Mont Blanc (monbl) presents a fixed
mountain in the same direction as the temporally
variable solstice. In assessing possible intentions, the Occam's razor
choice only needs correlate the
local factors, Avebury to Silbury Hill arc and the solstice
angle. These hypothetical intentional distances infer scaling the
earth accurately and likely, also, equating the Kennet
barrows arc to lunar orbit. Without
the question of knowledge of the bearing to a distant mountain entering
consideration, equating the monument arc length with another angle
infers accurately scaling the earth. Equating
the arc length with an astronomic constant does also, and adds the
inference of astronomical knowledge. No matter which inference,
scaling the earth is a significant accomplishment to ponder for 5,500
years ago, and a uniquely evidenced one too.
I end where I started—I
could use accurate GPS readings or survey equivalent. With intrasite
and intracomplex distances, the original builders could measure
directly and position precisely. To examine same, we need the same
resolution. Understanding
these awesome ancient monuments presents real challenges to both
method and theory. The greatest of them present geospatial relationships
uniquely evidencing prehistory and challenging our understandings
of the past. The two largest long barrows are no exception.
ArchaeoBlog
Related
Neolithic Posts
Readings, Sources,
Links
Stonehenge, Avebury
and Associated Sites UNESCO site.
Avebury
World Heritage Site, Kennet District Council "including
remains of the largest stone circle in the British
Isles, the longest stone avenue (West Kennet), one
of the longest Neolithic burial mounds (West Kennet
long barrow), one of the largest causewayed enclosures
(Windmill Hill), and the largest prehistoric mound
in Europe (Silbury Hill)."
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