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 230 27/ between them, which is the angle between the Celestial Equator and the Ecliptic. 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 to in such a way as to be parallel to the celestial equator, the axis around which the instrument rotates, is the polar axis.