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A group of observatories located in India, from the XVIII century.
"Jantar" comes from the Sanscrit word yantra and means "instrument", "Mantar" comes from mantra and means "formula", so both words means "instrument to calculate". It's the name of three of a total of five observatories built by order of prince Jai Singh II between 1724 and 1738, by the end of the Moghul Empire.
The sites are located at N and NW of the country: in New Delhi (the ancient seat of the Moghul Empire), Mathurā (now gone, the legendary city of Krishna), Varanasi (ancient learning center), Ujjain (the ancient capital city of Malwa province), and the most extensive one in Jaipur city (founded in 1726, capital city of Jai Sing's Empire). The last one was declared monument of national interest in 1968 by the Hindu government, and the measurements it provided were used for astronomic and astrologic purposes.
Made of wood, lime, stone and metal, the instruments are fixated on the ground. Because of the deterioration caused by tropical wheather, vandalism and war, several frequent restorations implemented some changes, for example in the addition of marble surfaces. The instrumens were made at high scale and allow locating the positions of celestial objects (luminaries, planets, stars and signs of the Zodiac). For that purpose, each yantra's measurements are based on the azimuth or the ecliptic, and some of them even include both references. The observations were also used for time measurements, so they provided the time hour, set the annual moment of equinoxes and predicted eclipses with only 2'' of difference. The instruments in Jaipur even added 1018 stars to the astronomic Islamic tables of Zij (XV c.).
For appreciating the functionality of each yantra, the site must be visited at daylight (so they cast shadows) and considered as a group of instruments where some of them complement the calculations of others. These are some of them:
1. Great Samrat Yantra
Samrat is translated as "The Supreme". It's the biggest sundial in the world, for measurements and calculations based on the Earth's axial rotation. Triangle-shaped, the hypotenus is parallel to the terrestrial axis and can be walked through a ramp. The staired ramp, across 74,14 ft long, points to the North Pole and ends in a parasol from where the directions of winds are observed, and eclipses are predicted.
To both sides of the ramp, a 49.21 ft long quadrant is parallel to the equator's plane. The ramp's shadow is casted on the perimeter of the quadrant, while it moves 13.12 ft/h (or 2.36 in/min). The perimeter counts on markers to read time passing by, every 6 h, 15', 1', 6'' and 2''. The instrument was also utilized to announce equinoxes.
The weight of the quadrants falls upon two underground chambers where the sunlight enters through holes on the walls and reaches a sextant. At midday, it can be set the Sun distance to the zenith.
There's also a smaller Samrat Yantra, third-size of the greater one, at the entrance of the site (North area, next to Nadivalaya Uttar, another instrument especially related to annual seasons). The small Samrat counts on 22.6 ft high, and the smaller division on the scales of the quadrants measures a 20'' period.
2. Great Jai Prakash Yantra
aerial and underground views
Jai Prakash is translated as "Light of victory". They are two big semi-spheres partially emerging from the ground, of 16.4 ft diameter each, and with some of the two systems of reference marked on the surface.
Each instrument includes gaps for an observer to walk through. If both instruments joined, the surfaces would form a continous sphere (where a sphere has a gap, the other one has a solid surface). Altogether, they offer a specular representation of the celestial dome.
The observer walks through the gaps and aligns the eye right on the surface where the object is marked on. Each band can be used during 1 hour, so when the terrestrial rotation makes the object not aligned with the surface (which means it moves beyond the area), the observer just has to go to the other semi-sphere to continue observing the position and path of the celestial object during the next hour.
semi-spheres in South-North orientation (Nadivalaya Uttar on the background)
Other two Jai Prakash Yantras can be seen to West of the Great ones, with some similarities and differences. The semi-spheres are smaller, have no gaps, and are oriented in East-West direction. But they offer both a celestial mapping and terrestrial measurements, either. For that purpose, two wires are crossed on each semi-sphere, oriented to the four cardinal directions. A small metal ring hangs from the intersection, thus indicating the zenith, so the shadow indicates the altitude and declination of the Sun. Around the surface, concentric circles indicate declinations.
3. Great Rama Yantra
The name tells it is "the instrument of Rama". Two drum-shaped cylinders count on elevated surfaces and a central pillar. Of 22.9 ft high and 11.15 ft wide, and like the Jai Prakash, they offer specular heavenly representations, either. Each building is made of 24 equal divisions, or 12 ground surfaces with 12 gaps between them, which allows the observer to walk inside. And, if both structures joined, they would complement each other, forming a single drum.
Walls and floors also count on marked scales. When drawing an imaginary line between the celestial object at sight and the apex of the central pillar, the inferior extreme of the same line points to a marking, which indicates the latitude of the object.
Digamsa means azimuth. Of smaller size, it complements the Great Rama Yantras although it doesn't provide a sky map. From the perspective taking the azimuth as a reference, it measures the altitude of objects. For that purpose, an object is observed from the point of view where two wires oriented to the four cardinal directions are intersected (such as in the Jai Prakash). Then, a string is tied to the central element and extended towards one of the outer cylinders, with some weight to produce tension. The string is moved across the outer border until gets aligned to the object on a vertical plane: a marking on the cylinders provides the altitude.
4. Rashi Valaya Yantra
Rashi Valaya means "zodiacal circle". It's a group of 12 structures, each one of them related to a zodiacal constellation. The designs are based on those of the Great Samrat, but the observations consider the ecliptic to set latitudes and longitudes, depending on the Earth's translation around its orbit. The instruments point to the sign of the Zodiac crossing the meridian at Jaipur, when the plane of the quadrants of some of the instruments is parallel to the plane of the ecliptic (the ramps are oriented to the North Pole of the ecliptic).
Paintings on inner arches of each ramp indicate the sign of the Zodiac assigned to each yantra (aprox. 11.81 x 14.96 in).
5. Kapala Yantras
(one of the Rama and Digamsa on the background
Kapala is a Sanscrit term referring to the brain part covering a human skull. The shape of these instruments, two big circular irons, reminds of it. Of 10.82 ft diameter, they're placed in between the small Jai Prakash. Supported according to the terrestrial axis, they hold within another axis although parallel to the plane of the equator.
But the instruments also consider the ecliptic reference. Like the Jai Prakash and Digamsa, the Northern iron (right side on the image) counts on two crossed-wires with a metal ring hanging from the intersection. The ring's shadow indicates the coordinates of the Sun but also the rising sign on the horizon, since the iron is engraved with 12 marked curves representing the rising signs.
Thus, the iron is marked with the two references for measuring. It's considered that the Kapala forerun the Jai Prakash, being the last one their unfolded reproduction. The Southern iron (left side on the image) has no observational purposes and it transforms visually the coordinates of one system into those of the other one.
6. Nadivalaya Uttar Yantra
aerial and side views
Nadivalaya is translated as "semi-spheric sundial". Two sundials are utilized to set the equinoxes seasons. For that purpose, each circular plate is aligned to the plane of the equator. During the Hindu Winter, the instrument oriented to the South is illuminated by the Sun. During the Hindu Summer, the same happens to the instrument oriented to the North. Luminic variations, during semestral periods, indicate the Earth's orbital translation.
The instruments also count on a thin stick, fixated in the center and parallely aligned to the terrestrial axis. The sticks cast shadows on the surfaces of the plates, whose outer perimeters include time markers for calculating midday and midnight moments, according to the Earth's axial rotation, and with an accuracy of minutes.
7. Raja Karika Yantra
(Unnatansha behind, and Dakshino Bhitti on the right background)
Raja Karika means "astrolabe of the King". Located at the Northern area of the observatory, it was made from a single copper piece. Of 7.97 x 6.92 ft, it weights more than 881 lb and is the biggest worldwide astrolabe of its kind!
On one of the discs (left background on the image), a sky map is engraved, whose outer perimeter displays divisions according to the ancient Hindu system to measure time: muhûrta = 48', ghati = 24', kâla = 48'', pala = 24''... During later restorations, that system was replaced by the Western measuring system.
8. Unnatansha Yantra
(Dakshino Bhitti on the background)
Unnatansha is translated as "elevation". To North the astrolabe, a big metal ring of 16.4 ft diameter hangs from a support and rotates around a vertical axis. The rotation allows observing celestial objects all across the 180° of the dome.
It's utilized along with a tube inserted in the hole at the center, as if it was a "sight", to set the altitude and declination of objects, at any moment of the day or night.
9. Dakshino Bhitti Yantra
Dakshino Bhitti se traduce como "muro de tránsito norte-sur". Se encuentra en el área noreste del observatorio, con uno de sus lados orientado hacia el Este y el otro hacia el Oeste. El lado Este incluye dos cuadrantes de unos 6 mts. de radio, y el lado Oeste es un semicírculo de radio un poco más pequeño. Una pequeña estaca perpendicular en el centro arroja su sombra al mediodía, lo que permite mayormente calcular la altitud del Sol con precisión de minutos.
Photos: Sketches and signs of the Zodiac from www.jantarmantar.org; Dakshino Bhitti West side by Swapnil Karambelkar (CC BY-SA 4.0, modified); Dakshino Bhitti East side by Chetan (CC BY-SA 3.0, modified).
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