JAIPUR - Jantar Mantar
Completo ed esaustivo (cliccare): Architecture_Science_Jantar Mantar web.pdf
Jai Singh has designed Jaipur strictly corresponding to the architectural rules of the Shilpa Shastra, an ancient idealistic Hindu doctrine. The city is divided into seven rectangular areas following the caste system and preordination. In the 7th, most centered area lies the Palace, which houses the womens chambers and the holiest sanctum. Differing from the Shilpa Shastra rules, in this holy area Jai Singh created not a temple, but the Jantar Mantar. His capital city and observatory are, in spite of Jai Singh II's scientific and political cosmopolitanism, of purely religious origin, a fact which is often ignored or forgotten.
materialisaton of an idea
The observatory consists of oversized stone observation devices,
which get a good degree of accuracy due to their enormous
dimensions. It is the biggest of five observatories, which Jai Sing
II had built. The majority of the devices is typical for big
observatories in the Islamic world. The most significant one, built
by famous Ulugh Begh (1394-1449) in Samarkand has been an inspiring
example for Jai Singh. But his instruments are unique as concerns
precision, size and architectural perfection.
Several devices, first and foremost the hemispheres of Jai Praksh Yantra set in the ground, however, are attributed to Jai Singh as new constructions. Basically it is one marble hemisphere set in the ground about 4 metres in diameter - in itself a master piece - where above a cross with a metal ring is applied. The inside surface is covered with coordinate lines. During the day the shadow of the metal ring allows to read the exact position of the sun on the coordinate lines, and of course the time. During the night a simple tube was used as a sighting device for observation.
Jai Praksh Yantra
The observer lays down in the hemishere and focuses on the stars through the sighting tube, whose end is held by the metal ring. The elongation of the tube onto the sphere's inside surface shows a star's position by reading the coordinate lines. To simplify measurement - one person has to adjust, while the other has to hold the tube - the Jai Praksh Yantra is made of two hemispheres, themselves complementary. In place of the passages in one hemisphere threre are marble scales of the other and vice versa. Alternating use of the hemispheres within a two hours change allows observation around the clock.
The scale's centre is located 27 degrees below the edge. The connecting line between the scale’s centre and the metal ring points exactly to the Celestial North Pole. Proceeding from that point equatorial coordinates of the celestial bodies can be read. The circle around the centre shows the position of the Ecliptic Pole througout the year. It helps determining celestial coordinates, too. All those observations of the sky are feasible just with the Jai Praksh Jantra. Maybe it is Jai Sing’s major work, particularly because it lies in the centre of Jantar Mantar and further westward another smaller model is located.
it's own observatory
The apparent orbit of the sun around the earth - that is in fact the orbit of the earth around the sun - is called ecliptic. It is devided into 12 equal parts named the zodiac circle. The angle of 23 degrees between the ecliptic and the equator brings about the seasons as the variing length of day and night. On June 21 the summer solstice is in the northern hemisphere and with it the longest day. In the southern hemisphere it is winter solstice on June 21 with the shortest day. The sun stands vertically above 23 degrees northern latitude (Tropic of the Cancer). On March 21 the sun stands vertically above the equator, so day and night is identical.
Eversince equinoxes are of exceptional importance for astronomers. These are the only days under identical circumstances all over the world. Day and night are exactly of the same length. The sun rises stricly in the east and sunset is strictly in the west. During the equinoxes both poles of the earth lie over the ecliptic so both northern and southern hemispheres of the earth are lighted equally. In the course of the year the northern and southern hemispheres are lighted unequally. Beyond the polar circle the day and night side is permanently lighted for six months on each hemisphere (polar day).
From the earliest period until today the vernal equinox was a reference point for position data. It can be dertermined in a relatively easy way at any place due to the point of sunrise on the eastern horizont and the point of sunset on the western horizont define a line straight through the oberserver's position on that day. Prehistoric observatories (Stonehenge) are orientated towards the vernal equinox. Depending on the world picture the vernal equinox defines a point on the horizont, on the sun's orbit or on the earth's orbit. The peculiarities of the coordinate systems are caused by these differences in the point of view.
The easiest way to define a star's celestial position is in relation to the horizont line and the point of vernal equinox. Due to the rotation of the earth these position data are valid only for a certain observer's location, time and date. Observation of periodically recurring events in the sky (the sun's orbit, lunar phases, venus' rise and set as morning and evening star, comets) allows to determine the seasons up to developping a precise calendar, but results are fixed to a certain location. With every change of location new observation is neccesary. This is why the horizont system cannot be used for navigation purposes.
A point of reference that is independent from the observer's location is offered with the Celestial Pole. All stars seem to rotate arround it due to the earth's rotation. As the earth's axis is in circular motion itself, the Celestial Pole rotates around the Ecliptic Pole once in about 28850 years. In the equator system the celestial equator that is standing rectangular to the celestial pole is used as second point of reference. A star's position is defined by its height over the equator and angle to the vernal equinox. Since the vernal equinox is defined as a point on the celestial equator, it moves on the ecliptic as the celestial pole rotates.
The apparent movement of the vernal equinox on the ecliptic is caused by the geocentric point of view the equator system is based on. The rotation of the celestial pole around the ecliptic pole as seen from the earth leads to a slow rotation of the zodiac signs around the zodiac circle. This is known since the antiquity (Platonic Year, 25850 years). As seen from the sun, the vernal equinox is a point on the orbit of the earth. The ecliptic system defines the position of a star in relation to the vernal equinox and the ecliptic. Within the solar system these position data are practically absolute.
Gnomes, shadow indicators, are actually sundials. There are differences between the 14 gnomes of the Jantar Mantar in their function, but not in principle. With a sighting stick that rests against the quadrant and the ramp a celestial body is aimed at. At the bearing points of the sighting stick position data can be read from engraved markings. Depending on the orientation of the ramp to a point over the horizont, to the Celestial Pole or the Ecliptic Pole one can read position data corresponding to the horizont, equator or ecliptic system. Additionally time can be determined from the ramp's shadow.
Over 30 metres in height, the big sundial is the most impressive and the biggest device. The ramp that forms the indicator is orientated to the north. It's gradient of 27 degrees is equivalent to the latitude of Jaipur. Thus the ramp points exactly to the Celestial North Pole. The shadow of the indicator falls of the wing-shaped western and eastern scales. They are made of marble as the side edges of the indicator are, and covered with delicate measuring divisions. According to the size and architectural precision, the shadow shows the local time accurate within four minutes. Using a sighting stick accuracy lies within seconds.
With a sighting stick or a little shadow stick that is moved along the stairs until the shadow just touches the edge of the quadrant, the distance in degrees of the sun or other stars from the equator can be measured. This method allows the determination to the minute of equinoxes and solstices which are of central meaning for all religious astronomical and astrological world systems. By the way, the ramp is sealed off from visitors. It is still used by priests for observations. The little sundial however is open to the public. It might have been intended for everday purpose.
Westward from Samyat Yantra there are 12 smaller gnomes about 3 metres high that are pointing at different directions. They are used to determining celestial coordinates. Their ramps are not orientated to the Celestial Pole but to the Ecliptic Pole. The quadrants lie in the plane of the ecliptic. Because the Ecliptic Pole appears to rotate around the Celestial Pole the ramp can only be oriented to the Ecliptic Pole for one fixed date. Each of the 12 gnomes points towards the position of the Ecliptic Pole at the beginning of a zodiac sign. With these 12 points of measurement calculation of position data for every day is possible.
Among many further devices, the big astrolabe should be particularly mentioned. It is a star chart engraved in a metal disc. Moveable rulers allow similar to a slide rule the calculation of rising and setting points as to convert coordinates and work out horoscopes. With a sighting tube the zenith distance of a star can be determined as well. Standard astrolabes are between 30 and 50 cm in diameter whilst the astrolabe of Jai Singh is around two metres in diameter. Jai Singh specially developed an alloy made of seven metals that prevents alternations in size due to warming up of the sun.
Unfortunately there is only a few that has been written about this uniquely integrating work of art, science and religion, though it is used to be mentioned in special literature as extraordinary. Maybe there is no real interest in pointing out Jantar Mantar's consequences. After all the claim to scientifc omnipotence of the enlighted modern times is seriously relativated by Jai Singh's religious-scientific intention. Most of the devices of the Jantar Mantar are limited to the means of a highly developed Stone Age culture. They might as well have stood in Egypt, in South America or in Stonehenge.
Anyone who wants to know more about the Jantar Mantar should simply visit Jaipur. At the ticket office the only literature about the Jantar Mantar I know is available, "Astronomical Observatory of Jaipur by Daulat Singh Rajawat" and "Stone Observatories" by Prahlad Singh.
Modelli 3D e Virtual Tour su: http://www.jantarmantar.org/
Completo ed esaustivo (cliccare): Architecture_Science_Jantar Mantar web.pdf