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The Krantivrtta is an instrument that can measure the ecliptic co-ordinates - Celestial Latitude and Celestial Longitude.

The annual apparent path of the Sun in the sky is the Ecliptic, which forms the basic framework of the ecliptic co-ordinate system.

The projection of Earth’s Equator in the sky, is the Celestial Equator. The Celestial Equator and the Ecliptic intersect at two points in the sky – the Vernal Equinox and the Autumnal Equinox.

The Celestial Latitude of a body in the sky is its angular distance in the direction North or South, of the Ecliptic. The Celestial Latitude is measured along a great circle passing through the body and the ecliptic poles. The Poles of the Ecliptic are two points in the celestial sphere that are 900 away from every point on the Ecliptic.

The Celestial Longitude of a body is its angular distance from the Vernal Equinox, measured along the ecliptic. The celestial longitude is measured toward the East, from the Vernal Equinox to the point of intersection between the Ecliptic and the great circle that passes through the celestial body and the ecliptic poles.

The Krantivrtta at this location in the observatory was built during the 1901 renovation of the observatory, as the original masonary krantivrtta (near the entrance to the observatory) could not be completed.

The Krantivrtta is an interesting instrument that can determine the Celestial Latitude and Celestial Longitude of an object in the sky. The instrument consists of two brass circles, one representing the Celestial Equator and the other representing the Ecliptic. The two circles are mounted with an inclination of 23.5 degrees between them. The entire brass instrument, with the two mounted circles, can rotate around an axis that is perpendicular to the masonry face on which the instrument rests. Since this masonry face is inclined in such a way as to be parallel to the celestial equator, the axis around which the instrument rotates, is the polar axis.

Using the sighting bar and arc placed on the outer brass circle, one can align the instrument towards the object to be observed and note its Celestial Longitude and Celestial Latitude on the corresponding scales.

By rotating the entire instrument around this polar axis, the ecliptic ring is made parallel to the ecliptic at any given moment. There is a sighting bar that is pivoted to the ecliptic ring and which can be rotated around the ecliptic pole, when the whole instrument is in such a position that the ecliptic ring is parallel to the ecliptic. With this rotation of the sighting bar, the celestial object under observation is bought into view. The reading on the ecliptic ring, where the sighting bar rests, gives the Ecliptic Longitude of the object.

There is a quadrant attached to the sighting bar. There is a smaller sighting bar with this quadrant, which when aligned towards the celestial object, allows one to read off the celestial latitude of this object on the quadrant scale.

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Page last modified on September 04, 2008, at 09:32 PM EST