The north-south passage of the Sun marks the seasons. This instrument measures the movement of Sun. The dial reads the north-south coordinate called the declination at noon, the meridian transit of the Sun. When the Sun has a declination exactly equal to the latitude of the place it will be at zenith at noon. For Bengaluru this is 130N as can be read out from the dial. It happens on April 25th and August 18th every year when there is no shadow at noon.
Dakshinothara Bhitthi are seen at Jai Singh’s Observatories in Varanasi, Ujjain, Delhi and Jaipur.
Dakshinothara Bhitthi consists of a graduated semicircular strip fixed on a wall aligned with the North- South line of the Earth’s rotation axis. A flat, long rectangular strip with a hole in the middle is fixed on to the top of the North-South wall. The sun rays passes through this hole and falls on the graduations of the semicircular strip.
Due to the tilt in the Earth’s rotation axis, the Sun itself appears to move from 23.50N to 23.50S. Everyday as the Sun crosses the meridian, the position of the light spot indicates this annual North- South movement of the Sun called declination. The readings can be read out from the dial.
On two specific days in a year, the light beam falls vertically down to read 130. These are the zero shadow days when the declination of the Sun is equal to the latitude of the place.