As the sun traverses the peacock blue sky, the shadow of this immense needle crawls across the face of an engraved half-moon of stone at a rate of one millimetre per second, a hand’s breadth every minute. Its movement tells local time to within a margin of error of around two seconds.
The gnomon of the Vrihat Samrat Yantra – the Great King of Instruments – is a stepped masonry ramp soaring 27 m into the sky at an angle of 26° 55′, matching the latitude of the city of Jaipur. Pigeons roost in arches cut from the peeling saffron plaster of the structure’s flanks. It is topped by a chhatri, a canopied pavilion from which eclipses and the arrival of the monsoons are announced. As the sun traverses the peacock blue sky, the shadow of this immense needle crawls across the face of an engraved half-moon of stone at a rate of one millimetre per second, a hand’s breadth every minute. Its movement tells local time to within a margin of error of around two seconds. It is tempting to assume that the monumental size of the sundial at Jantar Mantar increases its accuracy, but given that the penumbra of the sun can be as broad as a fingertip, the delicate calibrations are more ornamental than functional. Its scale is rather an expression of the power of knowledge.
Jantar Mantar is a corruption of the Sanskrit यन्त्र मन्त्रण yantra mantrana – ‘calculating instrument’ or ‘consulting machine’. Jaipur houses five major instruments – Vrihat Samrat Yantra, Ram Yantra, Jai Prakash, Digamsha Yantra and Narivala Yantra – and 15 lesser instruments used to calculate the time of sunrise and sunset, the procession of the seasons, eclipses, and the position of various planets, stars, and constellations. Built in the early 18th century, the instruments are arrayed in one of the many interlocking courtyard gardens of Sawai Jai Singh II’s palace to the northeast of the Old City. He is portrayed in exquisite miniature in the royal Rajput attire of jama, patka, and mauli; flared knee-length overgarment, ornate embroidered girdle, and red turban. His ears are pierced, his moustache is luxuriant, a jewelled scabbard nestles at his hip. This devout follower of the Vaishnav sect ascended to the throne of the Kingdom of Amber in 1699 at the age of 11. He was simultaneously a traditionalist and reformer. While he was the first Hindu ruler in seven centuries to enact the ancient Vedic aśvamedhá horse sacrifice, he abolished the practice of sati where widows are expected to hurl themselves on their husbands’ funeral pyres. He also pressed the Mughal Emperor Muhammad Shah to end the jaziya and Hindu pilgrimage taxes. Fiercely intellectual, Singh believed that an education in the ancient Indian art of astronomy was vital. In the midst of invasion from the north and an inner turmoil that eventually tore the Mughal Empire apart, he built five monumental observatories all named Jantar Mantar. Only largest of the observatories, at his capital city Jaipur, is still fully functional.
Jai Singh II’s manifestation of astronomical wisdom in grey-veined marble, red brick, and yellow brass was intended to celebrate the renewed vigour of a tradition stretching back millennia. In fact, it marked the beginning of its final days. The sundial has its roots deep in history and may have been invented more than once. In the sixth century BCE a geographer and mathematician named Anaximander introduced the Babylonian theory behind sundials to Greece. In India, meanwhile, the first mention of the gnomon – named shanku or ‘cone’ in Sanskrit – appears in the Vedāṅga Jyotiṣa. This text describes a winter solstice some eight centuries before the time of Anaximander, pointing to an indigenous Indian innovation – or at least a separate transmission from Babylonia. But as critics quite rightly point out, there is no proof that updated calculations weren’t incorporated into the text at a much later date. Both Hindu and Buddhist scriptures from the Middle Ages contain less controversial evidence of exposure to Greek and Roman scholarship. The resulting synthesis was, in turn, exported over the mountain passes of the Himalayas into China with the expansion of Buddhism. In the 1500s, the Mughal emperors thundered south from Persia, bringing huge swathes of the Subcontinent under their banner. This often uneasy marriage between Islamic and homegrown traditions saw a new flowering of Indian astronomy with the coupling of observational instruments from the Muslim World and Hindu mathematical understanding. Almost 100 new treatises – known as zīj – were added to a library stretching back to eighth century Baghdad under the Abbasid Caliphs. One of the latest and most famous of these – noted for its discussion on the use of telescopes – was the 400 page Zīj-i Muhammad Shahi named for a Muslim scholar at Jaipur’s Jantar Mantar. The pursuit of positional astronomy united India with the Middle East, Africa, Asia, and the Mediterranean for more than 15 centuries during which the forces of politics, religion, and science all looked to the skies as their source of their authority. Less than a century after it was completed, however, Jantar Mantar slid into obscurity and then disrepair. A new power and a new world view was rising on the horizon, marked by the ticking of a different type of clock.
The Equation of Time
If the Earth’s orbit around the Sun were a perfect circle, then sundial time and standard clock time would be in synchrony. The reality of an elliptical orbit, however, means that there are only four days per year when no adjustment is required. On other days of the year, the difference between mean time and apparent time can be as large as 15 minutes. The Equation of Time provides the information needed to reconcile the two, and while it is applicable to sundials the world over, it needs to be constantly updated. Slow changes in the Earth’s annual trajectory mean that while a 15th century sundial might still be accurate, a 21st century calculation would be needed to read it. Some sophisticated sundials now incorporate the Equation into their mechanisms. The Equation of Time has been around ever since the invention of accurate clocks in the mid-1600s. The direction of its use, however, has shifted dramatically. Until 1800, sundial time was considered ‘right’ and the clocks were considered ‘wrong’, so the Equation was originally used to ‘correct’ clocks and bring them into line with the time shown on the sundials.
