Jantar Mantar, Jaipur

A prince and his observatories

Sawai Jai Singh II (1688–1743), ruler of Amber and founder of Jaipur, was a patron of astronomy who found the tables he inherited in disagreement with the sky. He had instruments built at five cities, Delhi, Jaipur, Ujjain, Varanasi and Mathura, of which the Delhi and Jaipur observatories are the largest. The Jaipur observatory was begun around 1728 and the main construction period ended around 1734, though work is reported to have continued to 1738.

He had been dissatisfied with the small brass instruments of earlier astronomers, whose graduations were too coarse for the precision he wanted. His answer was to build large and in stone, so that a degree became a measurable length and a fixed foundation could not drift.

Instruments as architecture

The Jaipur observatory has 19 instruments, among them the Samrat Yantra, a giant sundial, and the Jai Prakash Yantra, a pair of hemispherical bowls in which the sun's shadow falls on a marked surface. Stairs lead to the top of the Samrat Yantra, whose gnomon is angled to the latitude of Jaipur, so that its shadow moves along a graduated quadrant at a rate of about one millimetre every second, as the guides say.

Others measure the sun's declination, the zodiac sign at the meridian or the time in local mean units. Because each instrument is built to a single latitude and a single purpose, the whole observatory works as a set of analogue computers that give a direct reading with no calculation.

Preservation and recognition

The instruments were restored in 1876 under Maharaja Ram Singh and the site was declared a national monument in 1948. UNESCO inscribed Jantar Mantar, Jaipur, on the World Heritage List in 2010, calling it the most significant, most comprehensive and best preserved of India's historic observatories. Today the Government of Rajasthan runs the site as a museum, and visitors can read the time from the Samrat Yantra to within about two seconds.

Reading the instruments today

The Jaipur instruments were designed to be read by eye, in the open, by observers who climbed the stairs. A modern visitor can still use the Samrat Yantra to tell the time, or follow the sun's declination on the Rama Yantra, though not with the precision that an electronic clock gives. The observatory also carried a social meaning: it was used to calculate the calendar and to fix the times of ceremonies and astrological decisions, as well as to correct astronomical tables. Jai Singh's astronomers also compared their results with the European tables that his envoys had brought. The site is a reminder that precision and ritual were not separate uses.

Instruments and technologies

• Samrat Yantra A giant equinoctial sundial: a triangular wall angled at the latitude (about 27 degrees north), with a graduated quadrant on each side on which the shadow of the edge moves with the sun.
• Jai Prakash Yantra Two hollow hemispheres marked with the sky's coordinates; an observer sees the shadow of a wire crossing the bowl and reads the sun's position directly.
• Rama Yantra Paired cylindrical structures in which the altitude and azimuth of a body is read from the shadow or by sighting.

The people

• Sawai Jai Singh II Ruler of Amber, founder of Jaipur and builder of the five observatories.

Timeline

• 1728 Several instruments are in place.
• 1734 Main construction period ends (work is reported to continue to 1738).
• 1876 Restoration completed under Ram Singh.
• 1948 Declared a national monument.
• 2010 Inscribed on the UNESCO World Heritage List.

Key lessons for observation today

• Bind the instrument to the site The instruments work because they are cut to Jaipur's latitude. A modern installation records the site's coordinates and datum so that a reading can be reproduced.
• Read it out directly Visitors read the time without calculation. A good instrument interface hides the arithmetic and shows the quantity.
• Keep the record of restorations Restoration in 1876 and in later years changed the instruments. Changes are part of the data's history and belong in its metadata.

Sources

• Wikipedia, Jantar Mantar, Jaipur
• Wikipedia, Jai Singh II
• UNESCO World Heritage Centre, The Jantar Mantar, Jaipur