Jantar Mantar is a group of astronomical observatories built in the early 18th century by Maharaja Jai Singh II, a ruler of the Rajput kingdom of Amber, in what is now Jaipur, Rajasthan, India. The observatory at Jaipur is the largest and most well-known of the five observatories built by Jai Singh II and is home to the world's largest sundial.

The name "Jantar Mantar" comes from the Sanskrit words "yantra" (instrument) and "mantra" (formula), indicating that the instruments were used to measure time, predict eclipses, and track the movements of celestial objects.

The sundial at Jantar Mantar is known as the Samrat Yantra, which means "Supreme Instrument" in Sanskrit. It measures time with remarkable accuracy, to within two seconds of the actual time of day. It is 27 meters tall, with a base of 16 meters in diameter.

The Jantar Mantar at Jaipur was constructed between 1727 and 1734 and was designed to be used for astronomical observations, particularly of the movements of the sun, moon, and stars. Jai Singh II, who was an accomplished astronomer and mathematician, wanted to create a set of instruments that were accurate and reliable, and that could be used to make precise observations of the heavens.

The observatory at Jaipur is a complex of 19 large instruments, each of which is designed to measure a different aspect of astronomical phenomena. These instruments are made of local stone and marble and are arranged in a vast open space that is nearly 30,000 square meters in size.

The sundial consists of a triangular gnomon (a vertical rod) that casts a shadow on a set of marked marble slabs that form a circular platform. The shadow moves at a constant speed, and the position of the shadow indicates the time of day, with markings corresponding to each hour of the day.

The Samrat Yantra is the largest sundial in the world, and its design reflects the sophistication of ancient Indian astronomy. The sundial is aligned with the North Pole, and its angle is set to the latitude of Jaipur. The markings on the slabs take into account the Earth's axial tilt and the equation of time, which corrects for the difference between solar time and clock time.

The Samrat Yantra is not only a marvel of ancient engineering but also a testament to the scientific achievements of ancient India. It is a reminder that India was once a hub of scientific and mathematical knowledge and that its contributions to astronomy and other sciences are still relevant today.

The Jantar Mantar observatory is a UNESCO World Heritage Site and attracts visitors from all over the world. It is a symbol of India's rich cultural heritage and scientific legacy, and a reminder that the pursuit of knowledge is a universal human endeavor.

In addition to the Samrat Yantra, the Jantar Mantar at Jaipur also includes a number of other impressive instruments, including the Jai Prakash Yantra, which is a pair of hemispherical bowls that are used to measure the position of the sun and stars; the Rama Yantra, which is a set of two cylindrical instruments that are used to measure the altitude and azimuth of celestial bodies; and the Laghu Samrat Yantra, which is a smaller sundial that can be used to measure time to within 20 seconds of accuracy.

The Jantar Mantar at Jaipur is a testament to the skill and ingenuity of the astronomers and mathematicians of ancient India. The instruments at the observatory are not only incredibly accurate, but they are also beautiful works of art that are finely crafted and ornately decorated. The Jantar Mantar is a reminder of the incredible scientific and cultural achievements of ancient India and is a testament to the enduring legacy of the country's rich scientific and cultural heritage.

Jai Singh and Astronomy

Jai Singh was born in 1688 at Amber in the region of Rajasthan that is now Jaipur. He ascended the throne when he was 12 years old, following the death of his father, Bishan Singh. The young king was bright, eager to learn, and socially and politically astute. Among his many later accomplishments, he founded the city of Jaipur which bears his name, and was responsible for much of its design.

India at this time was under the rule of the Mughals who distributed their power through the leaders of existing dynasties such as the Rajputs, Marathas, Pashtuns, and Sikhs. As a young man, Jai Sing, who came from the royal family of the Kacchawahas, led his troops to support the emperor Aurangzeb who was carrying out a campaign against the Marathas in the Deccan. It was during this campaign, around 1700, that Jai Singh met Pandit Jagannatha Samrat, who became his guru and later his chief advisor in matters of astronomy. At the end of the campaign, Jagannatha accompanied Jai Singh back to Amber, where he expanded his knowledge through the study of Jai Singh’s extensive collection of Islamic texts. As Jai Singh’s chief astronomer, Jagannatha was a major influence in the design of the Jantar Mantar, and the two men remained lifelong friends.

In the early 1700s, when Jai Singh conceived of his ambitious observatory project, the telescope had been in use by astronomers in Europe for over 100 years. Why then, did this highly educated ruler, who knew of the telescope and its applications in European astronomy, choose naked eye observation as the basis for his observatories?

One has to appreciate the culture in which Jai Singh lived. It is a culture that throughout its history has embraced the richness of sensory experience in its arts and sciences - exemplified in the precise and complex forms that developed in art, architecture, and music. Observation of natural phenomena, including the apparent movement of stars and planets, became a part of the Hindu worldview, and informed a myriad of life processes from agricultural practices, to religious rituals, to personal decisions of when and who to marry.

For astrologers, the tables known by the Arabic term Zij, which indicated the positions of the stars and planets at any given date and time, were critical to their practice. To create these tables, they used the astrolabe, an ancient instrument that can be used to map the local sky and make a variety of astronomical calculations. Invented by the Greeks in about 150 BC, and further developed by both Islamic and Indian astronomers, the astrolabe is an instrument both practical and beautiful. By the 14th century, Indian astronomers had perfected the instrument and were producing individual models with fine craftsmanship and beautiful ornamentation. Jai Singh would have received his early instruction in astronomy through the use of the astrolabe, and in fact, one of the early instruments at his observatory in Jaipur is the Yantraraja, a great Astrolabe approximately 8 feet in height.

In spite of the importance of the astrolabe in astronomical calculations, Jai Singh noted that the tables that had been created earlier were often not in agreement with current observations. His own research suggested that the brass instruments that had been used to establish the earlier tables may have lost accuracy due to the wear of their moving parts. It was in part, in reaction to this problem, and also through his own studies of geometric models, that Jai Singh conceived of an observatory with the stability and permanence of masonry, and the capacity for accuracy arising from the large scale.

Modern scholars of Jai Singh and his astronomy suggest there may have been other factors that motivated him. In the political turbulence of his times, it may have suited both his need to maintain good standing with the seat of power in Delhi and his need to maintain authority in his own region, to erect these monumental structures.

Observatory 

The observatory consists of nineteen instruments for measuring time, predicting eclipses, tracking the location of major stars as the earth orbits around the sun, ascertaining the declinations of planets, and determining the celestial altitudes and related ephemerides. The instruments are (alphabetical):^[2]

1. Chakra Yantra (four semicircular arcs on which a gnomon casts a shadow, thereby giving the declination of the Sun at four specified times of the day. This data corresponds to noon at four observatories around the world (Greenwich in the UK, Zurich in Switzerland, Notke in Japan, and Saitchen in the Pacific); this is equivalent to a wall of clocks registering local times in different parts of the world.)^[9]
2. Dakshin Bhitti Yantra (measures meridian, altitude and zenith distances of celestial bodies)^[9]
3. Digamsha Yantra (a pillar in the middle of two concentric outer circles, used to measure azimuth of the sun and to calculate the time of sunrise and sunset forecasts)^[10]
4. Disha Yantra (used to detect the direction)
5. Dhruva Darshak Pattika (observe and find the location of pole star with respect to other celestial bodies)^[10]
6. Jai Prakash Yantra (two hemispherical bowl-based sundials with marked marble slabs that map inverted images of the sky and allow the observer to move inside the instrument; measures altitudes, azimuths, hour angles, and declinations)^[2][9]
7. Kapali Yantra (measures coordinates of celestial bodies in azimuth and equatorial systems; any point in sky can be visually transformed from one coordinate system to another)^[5]
8. Kanali Yantra
9. Kranti Vritta Yantra (measures longitude and latitude of celestial bodies)
10. Laghu Samrat Yantra (the smaller sundial at the monument, inclined at 27 degrees, to measure time, albeit less accurately than Vrihat Samrat Yantra)^[10]
11. Misra Yantra (meaning mixed instrument, it is a compilation of five different instruments)
12. Nadi Valaya Yantra (two sundials on different faces of the instrument, the two faces representing north and south hemispheres; measuring the time to an accuracy of less than a minute)^[10]
13. Palbha Yantra
14. Rama Yantra (an upright building used to find the altitude and the azimuth of the sun)
15. Rashi Valaya Yantra (12 gnomon dials that measure ecliptic coordinates of stars, planets, and all 12 constellation systems)
16. Shastansh Yantra (next to Vrihat Samrat Yantra) This instrument has a 60-degree arc built in the meridian plane within a dark chamber. At noon, the sun's pinhole image falls on a scale below enabling the observer to measure the zenith distance, declination, and the diameter of the Sun.)^[11]
17. Unnatamsa Yantra (a metal ring divided into four segments by horizontal and vertical lines, with a hole in the middle; the position and orientation of the instrument allow measurement of the altitude of celestial bodies)
18. Vrihat Samrat Yantra (world's largest gnomon sundial, measures time in intervals of 2 seconds using the shadow cast from the sunlight)
19. Yantra Raj Yantra (a 2.43-meter bronze astrolabe, one of the largest in the world, used only once a year, calculates the Hindu calendar)^[12]

Major Attractions Within Jantar Mantar

The Jantar Mantar observatory in Jaipur comprises 19 instruments to measure the position and distances of extraterrestrial bodies. These instruments are basically stone structures, depicting interesting geometric shapes. It is advisable to take a local Jantar Mantar, Jaipur guide, or an audio guide for a clear understanding of the instruments and how they work.

Vrihat Smarat Yantra: The Huge Sundial

The Samrat Yantra, sometimes called “Supreme Instrument” is an equinoctial sundial of enormous proportion. Although one of the simpler instruments, and not too different from sundials which had been developed hundreds of years earlier, the Samrat Yantra is important because it measures time to a precision that had never before been achieved. The Samrat Yantra at Jaipur, for example, is capable of measuring time to an accuracy of two seconds. The essential parts of the Samrat Yantra are the gnomon, a triangular wall with its hypotenuse parallel to the earth’s axis, and a pair of quadrants on either side, lying parallel to the plane of the equator. On a clear day, as the sun passes from east to west, the shadow of the gnomon falls on the scale of the quadrant, indicating local time. You can see this illustrated in the time-lapse video below. Since a sundial gives the exact time for its particular locality only, a formula to obtain standard time is used that compensates for the longitude difference between the instrument location and its time zone, and the daily adjustment that must be made due to the earth’s orbit around the sun. The largest sundials are capable of extremely precise measurements of time by means of a special way of “reading” the shadow of the gnomon. One of the common criticisms of Samrat Yantra’s claim to precision is that because of the distance of the edge of the gnomon from the quadrant scale, its shadow has a soft edge. This means that although the surface of the quadrant is inscribed with fine markings to indicate 2-second time intervals, the soft edge of the shadow may span 6-7 of these marks and the center of the shadow can only be estimated.   The solution is to hold a thin object such as a twig or taut string parallel to the shadow edge and about a cm above the quadrant surface. Moving the rod into and out of the shadow, and noting the spot on the surface where its shadow disappears, gives an exact indication of the center of the shadow.  

Ram Yantra

The Rama Yantra consists of a pair of cylindrical structures, open to the sky, each with a pillar or pole at the center. The pillar/post and walls are of equal height, which is also equal to the radius of the structure. The floor and interior surface of the walls are inscribed with scales indicating angles of altitude and azimuth. Rama Yantras were constructed at the Jaipur and Delhi observatories only.

The Rama Yantra is used to observe the position of any celestial object by aligning an object in the sky with both the top of the central pillar, and the point on the floor or wall that completes the alignment. In the daytime, the sun’s position is directly observed at the point where the shadow of the top of the pillar falls on the floor or wall. At night, an observer aligns the star or planet with the top of the pillar and interpolates the point on the floor or wall that completes the alignment through the use of a sighting guide.

The floor is constructed as a raised platform at chest height and is arranged in multiple sectors with open spaces between them. This provides a space for the observer to move about and comfortably sight upwards from the inscribed surface. The instrument is most accurate near the intersection of floor and wall, corresponding to an altitude of 45 degrees. Here, the markings are at their widest spacing and give an accuracy of +/- 1’ of arc. For altitude readings greater than 45 degrees, the accuracy diminishes and diminishes to +/- 1 degree near the base of the pillar.

Among Jai Singh’s many contributions to sky observation, perhaps the greatest was the design of paired instruments such as the Rama Yantra and Jai Prakash at the Jaipur and Delhi observatories. These instruments incorporate inscribed surfaces at regular intervals, with equal space between them for an observer to stand to take readings. The instruments were exact complements (or opposites) of one another - where one had an inscribed surface, the other would have an empty space for an observer to stand. If you could lift one and superimpose it over the other, the surface would be continuous, since where one had a void, the other would have a solid, inscribed surface. In the Rama Yantra, the floor was constructed with either 30 (Delhi) or 12 (Jaipur) sectors. As a celestial object’s position changes, its position on the floor or wall also changes, and when the object’s position no longer aligns with an indexed surface (when it moves past the edge) the observer simply has to walk to the other instrument to continue the observation.

Jaya Prakash Yantra

The Jai Prakash may well be Jai Singh’s most elaborate and complex instrument. It is based on concepts dating to as early as 300 B.C. when the Greco-Babylonian astronomer Berosus is said to have made a hemispherical sundial. The smaller Kappala Yantra at Jaipur is an example of such a dial. See the time-lapse video below to see how the Kappala Yantra tracks the sun’s movement.

Hemispherical dials also appear in European Church architecture during the Middle Ages and at the observatory in Nanking, China in the late 13th century. The Jai Prakash, however, is much more elaborate, complex, and versatile than any of its predecessors.

The Jai Prakash is a bowl-shaped instrument, built partly above and partly below ground level, as can be seen in the drawing below. The diameter at the rim of the bowl is 17.5 feet for the Jaipur instrument and 27 feet for Delhi. The interior surface is divided into segments, and recessed steps between the segments provide access for the observers. A taut cross-wire, suspended at the level of the rim, holds a metal plate with a circular opening directly over the center of the bowl. This plate serves as a sighting device for night observations and casts an easily identifiable shadow on the interior surface of the bowl for solar observation. The surfaces of the Jai Prakash are engraved with markings corresponding to an inverted view of both the azimuth-altitude, or horizon, and equatorial coordinate systems used to describe the position of celestial objects.

Among Jai Singh’s many contributions to sky observation, perhaps the greatest was the design of paired instruments such as the Rama Yantra and Jai Prakash at the Jaipur and Delhi observatories. These instruments incorporate inscribed surfaces at regular intervals, with equal space between them for an observer to stand to take readings. The instruments were exact complements (or opposites) of one another - where one had an inscribed surface, the other would have an empty space for an observer to stand. If you could lift one and superimpose it over the other, the surface would be continuous, since where one had a void, the other would have a solid, inscribed surface. In the Jai Prakash, the hemisphere is divided into sectors representing one hour of observation (15 degrees). As the object being observed reaches the edge of one sector, the observer simply has to walk to the other instrument to continue the observation. Watch the time-lapse video below to see how this works! 

References:

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19. jantarmantar.org