Jantar Mantar is an astronomical observatory with masonary instruments, built in 1724 by Jai Singh, the mathematician and astronomer king. Sawai Jai Singh had noted that the astronomical calculations based on the existing planetary tables did not always agree with observations. The problem was especially serious with the appearance of the new moon, time of rising and setting of the planets, and the seasons of eclipses of the sun and moon.

JANTAR MANTAR

He built five observatories in total. They were at Jaipur, Delhi, Mathura, Ujjain

and Varanasi and were completed between 1724 and 1735. The one at Jaipur

was the largest with the maximum number of instruments. The observatory at

Mathura vanished sometime around 1850. Those at Varanasi and Ujjain exist in

various degrees of preservation.

JAIPUR DELHI

Sawai Jai Singh built many masonary

instruments. The Samrat yantra or the

'Supreme Instrument' is Jai Singh's most

important creation. The instrument is

basically an equinoctial sundial, which

had been in use in one form or the other

for hundreds of years in different parts

of the world. In India, Brahmagupta (AD

598) describes Kartari yantra, an

equinoctial sundial, which operates on

the same principle as the Samrat. Jai

Singh however, turned the simple

equinoctial sundial into a tool of great

precision for measuring time and the

coordinates of a celestial object.

SAMRAT YANTRA

SASTHAMSA YANTRA

Sasthamsa yantra is a 60 deg arc built in the plane of meridian within a dark chamber. The figure represents a dark chamber with a 60-degree arc facing south. The arc is divided into degrees and minutes. High above the arc, at its center on the south wall, is a pinhole to let the sunlight in. As the sun drifts across the meridian at noon, its pinhole image falling on the Sasthamsa scale below enables the observer to measure the zenith distance, declination, and the diameter of the sun. According to Kennedy, the instrument was invented by Abu Mahmud al-Khujandi in the late 10th century.

NADIVALYA YANTRA

Nadivalaya consists of two circular plates fixed permanently on a masonry stand of convenient height above the ground level. The plates are oriented parallel to the equatorial plane, and iron styles of appropriate length pointing toward the poles are fixed at their centers. The instrument is an equinoctial sundial built in two halves, indicating the apparent solar time of the place. It is an effective tool for demonstrating the passage of the sun across the celestial equator. On the vernal equinox and the autumnal equinox the rays of the sun fall parallel to the two opposing faces of the plates and illuminate them both. However, at any other time, only one or the other face remains in the sun. After the sun has crossed the equator around March 21, its rays illuminate the northern face for six months.

DIGAMSA YANTRA

Digamsa yantra, consisting of two cylindrical walls surrounding a central pillar, measures the angle of azimuth of a celestial body. Its central pillar as well as its walls are engraved in degrees and minutes at their top surfaces. Cross wires are stretched between the cardinal points marked over the outer wall. The observer uses one or more strings with one end tied to a knob on the pillar and the other end to stone pebbles suspended over the walls. The angular distance of the vertical plane from the north point, read on the scales, indicates the azimuth of the body . With these strings, the observer defines a vertical plane containing the cross-wire and the object in the sky. It was developed by Jai Singh.

RAMA YANTRA

The Rama yantra is a cylindrical structure in two complementary halves that measure the azimuth and altitude of a celestial object.. The cylindrical structure of Rama yantra is open at the top, and its height equals its radius. Both the interior walls and the floor of the structure are engraved with scales measuring the angles of azimuth and altitude. The scales are divided into degrees and minutes. There are radial and the vertical lines inscribed with scales for measuring the altitude of a celestial object. The two complementary units of a Rama yantra may be viewed as if obtained by dividing an intact cylindrical structure into radial and vertical sectors. The instrument is built in two complementary units The units are such that if put together, they would form a complete cylinder with an open roof.

RASIVALAYA YANTRA

The Rasivalayas are a set of 12 instruments based on the principle of the Samrat, which measure the latitude and longitude of a celestial object. A particular Rasivalaya instrument becomes operative when the first point of the sign of the zodiac it represents approaches the meridian. At that moment, its 'gnomon' points toward the pole of the ecliptic and its quadrants become parallel to the plane of the ecliptic. Because there are 12 signs of the zodiac, there are 12 Rasivalayas, representing each sign.

These are both multipurpose instruments consisting of hemispherical surfaces of concave shape and inscribed with a number of arcs. These arcs indicate the local time, and they measure various astronomical parameters, such as the coordinates of a celestial body. The engravings for coordinate measurement are identical on the surfaces of both Jaya Prakasa and Kapala A. They are inverted images of two spherical coordinate systems, namely, the azimuth-altitude, or horizon system, and the equatorial. The shadow of the cross-wire falling on the concave surface below indicates the coordinates of the sun.. The time is read by the shadow's angular distance from the meridian measured along a diurnal circle.

JAYA PRAKASA AND KAPALA ‘A’ YANTRA

A Dakshinottara Bhitti Yantra consists of a graduated quadrant or a semicircle inscribed on a north-south

wall. At the center of athe arc is a horizontal rod. The insrument is used for measuring the meridian

altitude or the zenith distance of an object such as the sun, the moon, or a planet. This is a modified version of the meridian dial of the ancients, which

was a portable instrument. With this instrument, the meridian altitude of the sun is discerned from the

shadow of the rod cast by the sun on the instument scale at noon on a clear day.

DAKSHINOTTARA YANTRA