The Ujjain Jantar Mantar vedshala is on the banks of the Shipra river inside a serene green enclosure.
The observatory consists of the Samrat Yantra, a small Nadivalaya Yantra, Digamsa Yantra, Dakshinottara bhitti yantra and a horizontal circular dial. The observatory complex now also houses a small Taramandal and is maintained by the Department of Education.
The Samrat Yantra
The Samrat Yantra is a sundial that can give the time to an accuracy of 20 seconds.
The shadow of the triangular wall of the Yantra, falling on the circular arcs, tells the time. This triangular wall, with the angle inside the wall equal to the latitude of this location, is placed exactly in the North South Direction.
The shadow of the triangular wall moves equal distances in equal time intervals, on the circular arcs. This movement is calibrated to read the time. The arcs are divided into 6 hours each, for the morning and the afternoon segments. The hours are sub divided into 1 minute divisions that are further subdivided into three 20 second divisions.
The Uttarayana and Dakshinayana annual movements of the Sun can also be measured, using the Laghu Samrat Yantra. The scales marked on its triangular wall are for measuring Declination - the angular position of a celestial object with respect to the equator.
Nadivalaya Yantra
Nadivalaya has two plates, facing North and South, which are the dials. The walls containing these plates are inclined towards the South at such an angle, that they are parallel to the plane of the equator of the Earth. The rods emerging perpendicular from the plates, are parallel to the axis of rotation of the Earth. The shadows of these rods move along the scales on the dial plate, indicating the time.
The entire dial plate, can be divided into time divisions. The zero of the scale is marked at the top and the bottom end of the dial plates so that one could read the time starting either from the solar noon or the solar midnight. To the time indicated by the circular scale, a correction factor for the day, needs to be added, to obtain the clock time.
Digamsa Yantra
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.
Dakshinottara Bhitti Yantra
The Dakshinottara Bhitti Yantra measures the Meridian Altitude of a celestial object, once in a day, as the celestial object crosses the Meridian.
The wall here is placed exactly in the North South plane. The Meridian or the arc defined by the North, South and overhead point, is in this plane. With the rotation of the Earth, when a celestial body crosses this arc, halfway between its rising and setting times, it is said to transit the Meridian.
The angular height of the object from the Horizon, as it crosses the Meridian, is its Meridian Altitude.
The instrument uses either the semi-circular arc built into the west facing wall, or the intersecting arcs of the East facing wall, to measure the Meridian Altitude of a celestial object. The Dakshinottara Bhitti Yantra measures the Meridian Altitude of a celestial object, once in a day, as the celestial object crosses the Meridian.
The wall here is placed exactly in the North South plane. The Meridian or the arc defined by the North, South and overhead point, is in this plane. With the rotation of the Earth, when a celestial body crosses this arc, halfway between its rising and setting times, it is said to transit the Meridian.
The angular height of the object from the Horizon, as it crosses the Meridian, is its Meridian Altitude.
The instrument uses either the semi-circular arc built into the west facing wall, or the intersecting arcs of the East facing wall, to measure the Meridian Altitude of a celestial object. The Dakshinottara Bhitti Yantra measures the Meridian Altitude of a celestial object, once in a day, as the celestial object crosses the Meridian.
The wall here is placed exactly in the North South plane. The Meridian or the arc defined by the North, South and overhead point, is in this plane. With the rotation of the Earth, when a celestial body crosses this arc, halfway between its rising and setting times, it is said to transit the Meridian.
The angular height of the object from the Horizon, as it crosses the Meridian, is its Meridian Altitude.
The instrument uses either the semi-circular arc built into the west facing wall, or the intersecting arcs of the East facing wall, to measure the Meridian Altitude of a celestial object.