o Sundial, calendar and Khmer temples Astro-archaeology = Astroarchaeology Solstice determination based on observations เขาพระวิหาร |
ABSTRACT:
The purpose of this paper is
the demonstrate by photos and calculations that it is impossible by
observations of the rising/setting sun or a gnomon to determine the two
annual solstice days.
On the solstice day and the day before and after the
sun appear to follow the same path, which in Indian mythology is
described as that Surya, the sun, rests for 3 days before continuing his
annual circle from solstice to solstice.
Determination of solstice in relation to ancient
megalithic structures in NE-Europe (Stonehenge, Newgrange, etc.) has
been described in the literature on
astro-archaeology by Alexander Thom in the 1970es and discussed in
detail in later considerations on archaeoastronomy (see literature
below)..
Solar observations at summer solstice 2007:
In 2007 it was winter
solstice the 21st of June at 06:59 (local time = UT + 7 h.).
One major obstacle doing solar observations around
summer solstice is that it falls in the rainy season. In 2007 the
monsoon came later than usual and for the first time in 10 years it was
possible to mark the southernmost path of the shadow of the sun on the
sundial, but it was not possible to take comparative photos of the
setting sun over a two-week period or not even for the five days around
solstice.
Field notes |
|
|
Date |
Observations |
Weather |
19 June 2007 |
Small movement
in the daily path observed (from the 18th to the 19th) |
Clear blue sky with a few
clouds |
20 June 2007 |
The sun
apparently follows the same path as on the 19th |
Clear blue sky with a few
clouds |
21 June 2007 |
The sun
apparently follows the same path as on the 19th |
Clear blue sky with a few
clouds |
22 June 2007 |
The sun
apparently follows the same path as on the 19th |
Clear blue sky with a few
clouds |
23 June 2007 |
The sun
apparently follows the same path as on the 19th |
Sunshine at around 8 to 9
in the morning |
24 June 2007 |
No
observations |
Clouds and rain |
25 June 2007 |
No
observations |
Clouds and rain |
|
|
|
21 June 2007, sunset |
|
29 June 2007, sunset |
Because sunset
observations were (and mostly are) not possible during the monsoon, we
have to rely on observations of the
gnomon shadow:
|
|
|
9 June 2007 at 8:05 (the stippled lines are
added) |
|
23 June 2007 at 08:24 |
Above:
Left: The paths of the shadow of the sun differ from
the 8th (red line) to the 9th (blue line).
Right: Two weeks later, around summer solstice the 21st, the daily
paths of the shadow appear to follow the same track. The 24th the
path changed slightly to the north, and the observer knows that
equinox was some days before.
|
CONCLUSION:
After 10 years of
experiments and observations of sunsets/sunrises the author
regards it as impossible to determine the solstice days by naked
eye observations no matter how long sight-lines are used.
Observations of the daily path of the gnomon shadow
gives similar result: Not until 2 days after solstice the
observer knows that the solstice was 2 days before.
|
|
|
A method to determine the solstice day in advance
If for some reason it is/was
required to know the solstice day in advance of time, then it is
possible to predict the day based on observations of the rising/setting
sun or a gnomon. The latter got the advantage of not being dependent of
a cloudless sky at the horizon and is also the only option on locations
where the horizon is obscured by mountains, vegetation or
constructions.
Background:
The 12th of December the daily path of the gnomon
shadow followed a previously marked line made the 1st of January - 20 days ahead.
Dividing 20 by 2 gives 10, which added to 11 gives 22 = the solstice
date.
Calculations confirm the observation: At solar noon the
apparent altitudes of the sun on the two above mentioned dates were
respectively 50°17'11'' and 50°17'24''.
The azimuth of the sunrises were 113°56'00''
and 113°56'40''. The azimuth of the
sunsets were 246°01'44'' and
246°03'35''.
The 12 December / 1 January line was marked on the
sundial, so next year the gnomon shadow will announce the solstice day
10 days in advance.
|
|
|
2008-01-01, sunset |
|
2008-01-02, sunset |
The pictures above
show the sunsets 10 and 11 days after solstice. When the sun
sets at the same location in December, the observer can easily
predict the date of the approaching solstice by adding 10 or 11
days. |
Literature |
|
Aveni, A. F.
|
World archaeoastronomy :
selected papers from the 2nd Oxford International Conference on
Archaeoastronomy, held at Merida,
Yucatan, Mexico, 13-17 January 1986. Oxford International
Conference on Archaeoastronomy (2nd : 1986 : Merida, Mexico)
Cambridge : Cambridge University Press, 1989 |
Brown, P. L. |
Megaliths : myths and men ; an
introduction to astro-archaeology. Poole : Blandford Press,
c1976 |
Heggie, D. C. |
Megalithic science : ancient
mathematics and astronomy in North West Europe, London : Thames
and Hudson, 1981 |
Heggie, D. C. (ed.) |
Archaeoastronomy in the
old world
Cambridge : Cambridge University Press, 1982 |
INDEX
12 January 2008
© Asger Mollerup
macsida@thai-isan-lao.com
www.thai-isan-lao.com
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