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The Chakra Yantra can measure the global co-ordinates of Declination and Hour Angle of a celestial object.

The Declination is the angular distance north or south from the celestial equator measured along a great circle passing through the celestial poles. Declination is positive in the northern half of the celestial sphere and negative in the southern half. A point on the celestial equator has a declination of zero.

Meridian is the great circle passing through the Zenith and the North-South points on the Horizon. The Hour circle of a celestial object is a great circle that passes through the body and the celestial poles. The angle between an observer's meridian and the hour circle of the celestial body is the Hour Angle.

The Chakra Yantra is a ring instrument that has been mounted and pivoted in such a manner that it facilitates the measurement of the global co-ordinates - Declination and Hour Angle of a celestial object. The mounting of this instrument is therefore, something like the equatorial mounting of a modern day telescope.

The ring is pivoted about a polar axis, at the South end of the instrument. A sighting tube is mounted, passing through the centre of the ring. The sighting tube of the instrument rotates about an axis that is perpendicular to the plane of the ring. Using the movement of the whole ring about the polar axis and the movement of the sighting tube about the perpendicular axis, a celestial object can be sighted.

The rim of the circle has divisions that indicate the Declination. For the Northern instrument, the Declination markings are in terms of larger divisions of 6 degrees and 1 degree and the smallest division is a tenth of a degree. The Southern instrument has divisions of 1 degree and is not subdivided further. The plate around the polar axis pivot has divisions with a least count of 1 degree that indicate the Hour Angle. Once the celestial object is sighted, the position of the sighting tube on the two scales can be used to read the Declination and Hour Angle.

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Page last modified on June 14, 2008, at 08:16 AM EST