Why Was It Built?
This
section explains the geometry and sightlines incorporated in Stonehenge.
You
may be surprised at the knowledge of our predecessors (-we were!).
Introduction |
Stonehenge must have been an impressive
meeting place for visitors from by far-flung tribes. Even so, most academics and scientists now
agree that it was also the Bronze Age equivalent of an astronomical
observatory. The Bronze Age people were trying to chart
the apparently random movements of the heavenly bodies, and to predict the
equinoxes and solstices that were so important in their lives, so that they
could gain a greater understanding of the universe they lived in. |
Sightlines |
Some of the sightlines shown in the diagram
above. |
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Aubrey Holes |
This is almost the most impressive feature
of Stonehenge, since it becomes obvious that the theories and calculations
for predicting lunar and solar eclipses were known to Bronze Age people
before any of the stones were even brought to the site, 5000 years
ago! This knowledge was completely lost to us
until the work of Copernicus and Kepler, 4600 years later! |
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In 1663 John Aubrey carried out the first
systematic inspection of the Stonehenge site, and the Aubrey Holes are named
after him. The holes are a metre wide and deep, and
were first thought to be 'post holes' for wooden posts. After human bones were excavated it was
seemed that they were intended as graves, but it is more likely that a
venerated foreman or official of the site was buried there in order to honour
him. In the 1960s the American astronomer Gerald
Hawkins was the first to propose that the Aubrey Holes were used in the
calculation of sun and moon eclipses. Astronomers now agree that the method later
proposed by Sir Fred Hoyle works correctly and accurately. The SUN stone is moved (anticlockwise) by 1
Aubrey Hole every 6 1/2 days. (6 1/2 x 56 = 364 days). Errors can be corrected at midsummer and
midwinter. The MOON stone is moved (anticlockwise) by 1
Aubrey Hole twice per day. (One cicuit would be completed in 28 days, a
lunar month.) Errors can be corrected by skipping holes in
rings at Station Stone 92 or 94. The NODE stones are moved (clockwise) by 1
Aubrey Hole every 4 months. When the SUN and MOON stones are together or
opposite, and the NODE stone is in a SUN or MOON hole, then there will be an
eclipse. The SUN, MOON and NODE stones could
originally be synchronised at the time of an eclipse. |
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What Is… |
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a Solstice? |
Solstice is a Latin (Roman) word meaning
'sun standing still'. This term refers to the time of year when
the Sun appears to stand still in its daily movement along the horizon. There are two Solstices each year, at
Mid-Summer and Mid-Winter. Summer Solstice 20th ~ 23rd June The Summer Solstice occurs on Mid-Summer's
Day when the Sun reaches its most northerly point, marking the longest day
and the shortest night in the Northern Hemisphere, before it begins its daily
march back toward the East for Autumn. Winter Solstice 20th ~ 23rd December The Winter Solstice occurs on Mid-Winter's
Day when the Sun reaches its most southerly point, marking the shortest day
and the longest night in the Northern Hemisphere, before it begins its daily
march back toward the East for Spring. |
an Equinox? |
Equinox is the Latin (Roman) word meaning
'equal night'. This term refers to the time of year when
the length of the day is equal to the length of the night (12 hours) and is
the mid-point between Mid-Summer and Mid-Winter (the Solstices). There are two Equinoxes each year (or
'Equinoces' to use the correct Latin plural). The Spring Equinox occurs at the mid-point
between Mid-Winter and Mid-Summer, as the Sun appears to rise each day
further and further North. The Autumn Equinox occurs at the mid-point
between Mid-Summer and Mid-Winter, as the Sun appears to rise each day
further and further South. |
an Eclipse? |
An 'Eclipse of the Sun' happens when the
Moon moves between the Earth and the Sun, so that the Sun's light is
obscured, and a shadow is thrown onto the Earth. An 'Eclipse of the Moon' happens when the
Earth moves between the Sun and the Moon, so that the Earth's shadow is
thrown onto the Moon. Either of these occurences would have been
quite terrifying to primitive peoples, and so the Bronze Age people would
understandably have been very keen to gain the skill of predicting eclipses,
in order to feel more in control of them, or at least to gain some
understanding of the process through repetition and measurement. |
Stage I/III? |
STAGE I Stage I in the construction of Stonehenge
was the period from 3100 BC to 2910 BC. During this time the enclosing Earth Circle
was dug, the Heel Stones and the Altar Stone positioned, and the Aubrey Holes
dug. STAGE II Stage II lasted from 2150 BC to 2100 BC, and
during this period the Blue Stones were placed and the Station Stones
positioned. STAGE III Stage III from 2100 BC saw the construction
of the great Sarsen Stone ring and the inner Trilothons. The Stages shown in 'How Was it Built' refer
to the sightlines which were possible at the time of Stage I/II (the Aubrey
Holes and Station Stones), and then a second sightline after the Sarsen Stone
ring and Trilothons were erected during Stage III. |