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Digamsa or the Azimuth, of a celestial object is a co-ordinate specifying its directional location in the sky. One can drop a perpendicular from the object, onto the Horizon, and mark this location P. Then, starting from the Direction North and moving Eastwards, one measures the angle when this point P is reached. This angle is the Digamsa or the Azimuth.

The Digamsa Yantra is an instrument that was built before the more sophisticated Ram Yantra, which can measure the Azimuth as well as the Altitude of a celestial object.

The Digamsa Yantra is a cylindrical instrument that has a very simple method of determining the Azimuth of a celestial object.

The instrument consists of a central pillar surrounded by two co-axial cylinders.

For determination of the Azimuth of a celestial object at night, a simple string is needed to be attached to a knob on top of the central pillar. This string is called the Drk Mandala.

The other end of the Drk Mandala string is then suspended over one of the outer cylinders, using simple weights. The circular rim of these cylinders is marked into degrees and further subdivisions, to indicate the Azimuth.

The Drk Mandala string is moved over the rim of any of the outer cylinders and aligned to sight the celestial object. By this process, a vertical plane is defined that contains the object and a point on the Horizon. The angular extent of this vertical plane from the direction North, can then be read from the marking on the rim of the cylinder where the string is resting.

The method of direct sighting should not be used to determine the Azimuth of the Sun, as it is harmful to look directly at the Sun. The Azimuth of the Sun can be determined by stretching cross wires over the surface of the cylinders. The intersection of the shadows of the cross wire and the Drk Mandala string would then indicate the position on the rim for determination of the Azimuth of the Sun.

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Page last modified on June 15, 2008, at 06:36 AM EST