Jai Prakash

  • Introduction
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    The Jai Prakash may well be Jai Singh’s most elaborate and complex instrument. It is based on concepts dating to as early as 300 B.C. when the Greco-Babylonian astronomer Berosus is said to have made a hemispherical sundial. The smaller Kappala Yantra at Jaipur is an example of such a dial. See the time lapse video below to see how the Kappala Yantra tracks the sun’s movement.

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    Hemispherical dials also appear in European Church architecture during the Middle Ages, and at the observatory in Nanking, China in the late 13th-century. The Jai Prakash, however, is much more elaborate, complex, and versatile than any of its predecessors.

  • How it works

    The Jai Prakash is a bowl shaped instrument, built partly above and partly below ground level, as can be seen in the drawing below. The diameter at the rim of the bowl is 17.5 feet for the Jaipur instrument, and 27 feet at Delhi. The interior surface is divided into segments, and recessed steps between the segments provide access for the observers. A taut cross-wire, suspended at the level of the rim, holds a metal plate with circular opening directly over the center of the bowl. This plate serves as a sighting device for night observations, and casts an easily identifiable shadow on the interior surface of the bowl for solar observation. The surfaces of the Jai Prakash are engraved with markings corresponding to an inverted view of both the azimuth-altitude, or horizon, and equatorial coordinate systems used to describe the position of celestial objects.

    Jaya Prakasa Elevation
    Jai Prakash perspective
  • Non-identical Twins!

    Among Jai Singh’s many contributions to sky observation, perhaps the greatest was the design of paired instruments such as the Rama Yantra and Jai Prakash at the Jaipur and Delhi observatories. These instruments incorporate inscribed surfaces at regular intervals, with an equal space between them for an observer to stand to take readings. The instruments were exact complements (or opposites) of one another - where one had an inscribed surface, the other would have an empty space for an observer to stand. If you could lift one and superimpose it over the other, the surface would be continuous, since where one had a void, the other would have a solid, inscribed surface. In the Jai Prakash, the hemisphere is divided into sectors representing one hour of observation (15 degrees). As the object being observed reaches the edge of one sector, the observer simply has to walk to the other instrument to continue the observation. Watch the time lapse video below to see how this works!

    Jai Prakash thumbnail

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