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Site: Nadivalaya

The south facing plate of the Nadivalaya

Moving eastwards from the Laghu Samrat Yantra and the Dhruvdarsaka Pattika, we then come to the Nadivalaya, another Equinoctial (or equal hour) sundial.

How does the Nadivalaya read the time?

Nadivalaya has two plates, facing North and South, which are the dials. The walls containing these plates are inclined towards the South at such an angle, that they are parallel to the plane of the equator of the Earth. The rods emerging perpendicular from the plates, are parallel to the axis of rotation of the Earth. The shadow of this rod, moves along the scales on the dial plate, indicating the time.

The dial plate facing the North

With the gnomon (the rod) being parallel to the axis of rotation of Earth and the dial plates being parallel to the equator of the Earth, the shadow of the rod moves equal distances in equal intervals of time, on the dial plate. The rods are therefore, like the triangular wall and the circular plates are like the arched quadrants of the Samrat Yantra.

The entire dial plate, can be divided into 24 equal hours and further subdivisions. The zero of the scale is marked at the top and the bottom end of the dial plates so that one could read the time starting either from the solar noon or the solar midnight.

The dial plate on the North facing wall has one scale marked on its outer edge. The scale has twelve large divisions on either side of the central diameter. The large markings are of 1 hour each. There are subdivisions indicating the minutes.

The dial plate on the South facing wall has three different concentric scales. The innermost scale has the time divisions in the Indian units of Ghatikas and Palas. The smaller divisions reads the time in steps of 10 palas.

1 Ghatika is equal to 24 Minutes and 1 Pala is equal to 24 seconds

The smaller divisions on the inner scale, therefore read time with an accuracy of 4 minutes.

The central scale in the red stone has larger divisions of hours and smaller divisions of 5 minutes, each.

The outermost scale on the South plate is similar to its counterpart on the Northern plate, reading time with divisions of hours and subdivisions of minutes.

Measure the time using any of the scales on the dial plates, add the correction factor for the day, as displayed under the Laghu Samrat Yantra, and then check against the correct clock time.

From the Autumn Equinox to the Spring Equinox, the dial plate facing south will be sunlit and is to be used for telling the time. From the Spring Equinox to the Autumn Equinox, the dial plate facing north is sunlit and is to be used for telling the time. Around the time of the Equinoxes, both the dial plates are seen to be sunlit. The transition of sunlight from the north plate to the south plate, signals the Autumn Equinox, while the transition from the south plate to the north one, signals the Spring Equinox. This interesting design of an equinoctial sundial, can therefore be used to note the onset of the two equinoxes.

There is a small European style Equinoctial sundial, having a traingular gnomon, with a flat dial on the ground, is placed on the top of the Nadivalaya.

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Page last modified on June 17, 2008, at 04:05 AM EST