THE AMAZING ARTISANS OF ANCIENT INDIA : A DETAILED STUDY ON THE ASTRONOMICAL SIGNIFICANCE OF THE GAVI GANGADHARESHWARA TEMPLE,BANGALORE. (Date built: 9th century AD)
Location of the temple in hanumanthnagar,Bangalore,Karnataka,India.
Gavi Gangadhareshwara (Gavi : cave, Gangadhara:river Ganga beholder, eshwara : Lord Shiva ) temple, Indian rock-cut architecture. Temple is famous due to the mysterious stone discs in forecourt and the exact planning allowing for Sun to shine on shrine in certain time of the year (i.e. two times per year - from 13 to 16 January in late afternoons and from 26 November to 2 December).
A Trident of Lord Shiva
Entrance to the temple
In front of the temple
Inside view’s of the temple
The annual phenomenon of sun’s rays falling on the shrine inside the cave
The Annual motion of the sun:
The annual motion of the sun is described by the change in the right ascension
(i.e. α - the east-west coordinate) and the declination (δ – The north-south coordinate) throughout the year.
Right ascension (
RA-
α) is the
astronomical term for one of the two
coordinates of a point on the
celestial sphere when using the equatorial coordinate
Declination (DEC- δ) in astronomy is comparable to geographic
latitude, but projected onto the
celestial sphere. Declination is measured in degrees north and south of the
celestial equator. Points north of the celestial equator have positive declinations, while those to the south have negative declinations.
- An object on the celestial equator has a declination of 0°.
- An object at the celestial north pole has a declination of +90°.
- An object at the celestial south pole has a declination of −90°.
The sun appears to move from north-south (δ) along the ecliptic is
expressed mathematically by the change of declination (δ) with longitude (λ) as
Sin δ = sin ε × sin λ
Where, δ - declination,
ε - the orientation of the rotation axis with respect to the plane of revolution (23.5°)
λ - the longitude of the sun.
We have four important points in the orbit,
Equinoxes (when δ = 0),
sin 0 = sin ε × sin λ
0 = sin ε × sin λ
i.e., sin ε =0 (or) sin λ =0
Solstices (when δ = ± 23.5°),
sin (± 23.5°) = sin ε × sin λ
± 0.3987 = sin ε × sin λ
For all latitudes within +23.5 < δ < –23.5, there are definitely two occasions when
the sun will have the same declination.
The direction of the sun’s rays at sunrise
can be calculated using the simple relation
Where, A - azimuth
φ - Latitude of the place
δ - Declination.
Bangalore: φ =12° 58' N (Latitude)
Thus, for Bangalore, there are two occasions in a year when the sun will have identical values of altitude and
azimuth. Thus the phenomenon of 14 January, namely the sun’s rays passing through the windows to reach the idol in
the cave, should recur on yet another date. This was observationally verified 30 November and December 1. While the 14 January event is much publicized, the other one is not even known. The verification was done both in 2006 and 2007, and reported.
OTHER FEATURES OF THE TEMPLE:
A unique feature of the temple are the two discs in the front yard called :
Surya Pana (sun disc) and Chandra Pana (moon disc)
The sun disc and moon disc parallel to each other
They are identical in size with diameter of about 2 m, parallel to each other. Orthogonal lines drawn on the discs on both faces resemble the cross-hairs in the eye piece of telescope. The supporting pillar has beautifully engraved bulls in a sitting posture.
Their orientation appears puzzling because
of several reasons :
1. Such discs have not been seen in any other temple.
2. The cross-hair-like engraving appears on either side of the disc.
3. They appear to be not aligned to the cardinal points.
Approximate floor plan of the temple as deduced by shadow measurements :
The shadow of the western disc gradually moved towards the eastern disc. However, if the orientation of the entrance was exactly west, the shadow of the western disc would have touched the eastern disc on days of equinoxes at sunset. The shadow remained quite far from the eastern disc on equinox days, but gradually moved towards it during June. This showed that the orientation of the entrance to the temple is not to the east as is common in many other temples. The shadow moved towards the eastern disc and almost made it during the summer solstice. Since the view of the horizon is blocked by the trees, tracking could not be continued till sunset. Marking the position of the shadow till the last possible minute further movement was calculated using the following formulae:
dz = (sin A. cosφ) dH
dA = {(cot z. cos A .cos φ) – sin φ} dH
where,
dz is the change in the zenith (height) distance
dA is the change in azimuth
dH is the change in the hour angle.
The shadow never crossed the eastern disc but retreated after June, giving a clue that the alignment is to the day of summer solstice. Thus now we are ready to draw up the floor plan.
Figure 1 : Approximate floor plan of the temple as deduced by shadow measurements
An approximate sketch of the floor plan as deduced from the observations appears in above Figure 1 . The orientation is clearly along a line quite different from the conventional NS or EW lines. The two large discs are aligned to the point of sunset on the summer solstice.
(Figure 2) explains this geometry of the solstices.
Observations were carried out around summer solstice. The position of the shadow was noted (photographed
whenever it was possible). The details are as follows. Let us consider
(Figure 3) for understanding the extrapolation done.
Based on the photograph of the shadow (Figure 4), we can represent two circles with centres at C and O to
represent the shadow and the eastern disc respectively. This was at a time prior to the actual sunset. Since the instant of sunset itself was not observable, we extrapolated the movement of the shadow using eqs (3) and (4). The shadow would
Figure 4 : Close-up view of the eastern disc on 21 June 2008 with the shadow of the western disc next to it. The photograph was taken at 6:05 pm about 40 min before sunset.
have then shifted by an amount equivalent to dA in the horizontal direction and dz in the vertical direction. This gives us C′, which would have been the centre of shadow at sunset. On the scaled-down version, this would be away from the actual centre O of the eastern disc by an amount x along the horizontal axis and y along the vertical axis. Observations were carried out on all days, whenever the weather permitted.
This is proof of the deduction about the alignment of summer solstice, since the diameter of the disc is about 2 m. These estimates are likely to have large errors owing to the fact that the shadow on the photograph is not in the same plane asthe eastern disc, but is on the rock which is about 3 m behind the disc. A closer look at (Figure 4)
shows that the shadow of the ‘Dhwajasthambha’ on the eastern disc about 40 min before sunset.
In fact, it exactly coincided with the vertical line of the disc. Its further passage to the edge, making way for the
shadow of the other disc could not be verified owing to the dimming of sunlight and the thick growth of trees closer to
the horizon. In the absence of verification at exactly sunset of summer solstice, it may only be conjectured that the discs were used to fix the day of solstice precisely. Therefore, we find that the Gavi Gangadhareshwara is unique because of the following reasons.
1. Alignment of the arch, windows and the Nandi to the sun’s rays of 14 January and also 30 November and/or December2.
2. Alignment of the two large discs to the summer solstice sunset, a fact which was hitherto unknown.
Now, Let us study the objective of this alignment in the construction of the temple as deduced from a different source.
Deductions from paintings of Daniell :
Portrait of Daniell
(a)Tracing of the painting of Thomas Daniell showing details of the front yard. (b) The same view now (it is not possible to accommodate all the features of the painting in the field-of-view owing to subsequent constructions).
In this context, two paintings of Thomas and William Daniell brothers provided valuable evidence7. The paintings depict the scene as in 1792, from two different angles. The first painting shows the region adjacent to the temple to the east; it is clear that the region was barren, devoid of any vegetation, providing a clear visibility to the horizon.
The second painting depicting the temple itself provides some more clues on the architecture. The painting is dated
1 May 1792. A tracing is shown in Figure 5 a and may be compared with Figure 5 b, a recent photograph. It is clear the temple has now undergone a facelift and in the process new walls and enclosures have been constructed. This prevents one to get an identical view today. It may also be noted that the ‘Dhwajasthambha’, a bronze pillar is a later addition. As we have noted earlier, the shadow of this falls on the vertical mark on the disc. Whether it was intentional or a coincidence (since there is no awareness or record of the introduction of this idea) is debatable, because it is an addition in the last two hundred years. The comparison also shows that the approach to the terrace of the temple (perhaps for monitoring the shadows of the discs) has been retained and the gentle slope along the rock has now steps cut along.
