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The Inclined Plane Sundials at the Jaipur Observatory
Introduction
Samrat Yantra - the King of Instruments

Construction: A large masonry structure of red sandstone and marble rising up to 90 feet above the ground. The gnomon consists of two walls inclined at 27° to the horizontal (being the angle of the latitude of Jaipur). The walls have steps between them. There is a scale up the walls for determining the altitude of the sun.

On either side are two quadrants inclined at 27° to the vertical (and thus in the plane of the celestial equator). The walls are ? feet long, and the radius of the quadrants is some 50 feet?. The quadrants are graduated in hours, minutes, and seconds. There are steps alongside the quadrants so that these graduations can be read accurately.

Use: The shadow of the left-hand wall falls on the left quadrant during the morning, and the shadow of the right-hand wall on the right quadrant in the afternoon. The shadow is not a sharp one, but has a penumbra due to the ½° angular diameter of the sun. This penumbra can be several centimetres wide, and the shadow is also moving at around ???cm. a minute. The instrument is marked out in segments of ???seconds






























These photographs show the extent of the penumbra of the shadow of the gnomon on the scale on the quadrants. The instrument has been undergoing restoration, which has resulted in some spots of mortar adhering to the scales, and thus also appearing in some of the photographs. The accuracy of the reading can be substantially improved by holding a thin rod, such as a toothpick, in the penumbra as shown in the right hand photo below and in movie clip 1 and movie clip 2








Laghu Samarat Yantra - the Small Sundial
The Small Sundial would be considered large in any other context than Jaipur. The construction and use of this sundial is exactly similar to the large instrument described above. The claimed accuracy of readings on this sundial is ± 20 secs.



















The Small Metal Sundial
This equatorial sundial made on metal is not mentioned in any of the guidebooks. Its gnomon is, of course, inclined to the horizontal at 27 degrees to the horizontal, the latitude of Jaipur.





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