A warrior-king who found every star table wrong, and built instruments of stone tall enough to correct them.
In the 1720s, the Rajput king of Amber had a complaint about the sky. The astronomical tables in use across Mughal India (Persian, Hindu and European alike) put the planets in the wrong places and missed the new moon. In a world where festivals, fasts and the business of empire ran by the calendar, that mattered. Jai Singh had already tried brass instruments, and found them too small to be trusted.
So he built in masonry. Across five cities he raised sundials, bowls and arcs on the scale of buildings, among them a gnomon 27 metres high. He sent an embassy to Portugal for the newest European tables. Along the way he planned a new capital on a grid. That city, Jaipur, still carries his name.
Soldier, courtier, astronomer
The lifeline
1688
Born 3 November, heir to the Kachhwaha kingdom of Amber in Rajputana
1699
Takes the throne at 11; Aurangzeb later dubs him “Sawai,” one and a quarter
1724
Completes his great observatory at Delhi, with the emperor’s blessing
1727
Founds Jaipur and sends an embassy to Lisbon for European tables
1734
His largest observatory, the Jantar Mantar of Jaipur, is completed
1743
Dies in Jaipur on 21 September, aged 54
By the numbers
The measure of him
5
Observatories: Delhi, Jaipur, Ujjain, Varanasi and Mathura
27 m
Height of the gnomon of the great sundial at Jaipur
~2 s
How finely that sundial is said to tell local time
19
Fixed instruments at Jaipur’s Jantar Mantar today
What he built and gathered
The work
1724
The Delhi Jantar Mantar, the first of his observatories to win the emperor’s backing. Its giant Samrat Yantra still stands near Connaught Place.
1727
Jaipur, a planned capital of broad, straight bazaars and walled blocks, laid out with the Bengali architect Vidyadhar Bhattacharya.
1727–30
An embassy to Portugal, led by the Jesuit Manuel de Figueredo. It returned with books, including Philippe de La Hire’s tables.
1728
The Zīj-i Muḥammad Shāhī, new astronomical tables dedicated to the emperor Muhammad Shah. They drew heavily on La Hire.
Sanskrit
Translations of Euclid and Ptolemy into Sanskrit by his court astronomer Jagannatha Samrat, bringing Greek geometry and astronomy to pandits.
Outrun by the telescope, then rescued
Recognition
After his death
Telescope-based astronomy was overtaking naked-eye work like his
His observatories fell into neglect; the one at Mathura has vanished
Jaipur’s instruments waited until 1901 to be restored, under Madho Singh II
Remembered as a king and city-founder more than a scientist
Today
The Jaipur Jantar Mantar became a UNESCO World Heritage Site in 2010
His walled city of Jaipur joined the list in 2019
Four of his five observatories still stand: Delhi, Jaipur, Ujjain, Varanasi
His tables stayed in use in India for about a century
The city he drew
Jaipur
His family had ruled for centuries from the hill fort of Amber. Jai Singh moved the court down to the plain and built a capital to plan. Jaipur has straight avenues, a walled grid of blocks, and an observatory beside the palace, where the king could watch the sky.
~11 km
From the old fort of Amber to the new city on the plain
1727
Year Jaipur was founded, the capital moving from Amber
2
UNESCO World Heritage Sites he left inside one city
“The tables in common use … the Hindu books, and the European tables, in very many cases, give … widely different results than those determined by observation.”
— Preface to the Zīj-i Muḥammad Shāhī, in Jai Singh’s name (trans. after W. Hunter)
