Maharaja Sawai Jai Singh II, the ruler of Jaipur between 1699 and 1743, was deeply interested in astronomy and constructed observatories at Delhi, Jaipur, Ujjain, Varanasi and Mathura. The Delhi Jantar Mantar was the first, and even three centuries later, its instruments yield fairly precise readings.

Four instruments, constructed as six brick-red structures, spread out across Jantar Mantar amidst neat gardens. Smart steel signs stand beside each instrument, describing its history, function, and working. If you’ve a passable understanding of astronomy, these should be sufficient. Otherwise, hire a government-approved guide from near the ticket counter.

The first instrument, a heart-shaped one that was the emblem of the 1982 Asian Games, is the Misra Yantra. This is a composite instrument, built probably by Jai Singh’s son Madho Singh. The Misra Yantra is unique to Delhi—the other Jantar Mantars don’t have it. Besides indicating local time, it measures different aspects of a celestial body: meridian altitude; declination during movement across the sky; and longitude.

Beyond the Misra Yantra is a depression, with masonry arcs rising on both sides and a tall staircase, like a giant triangle, between them. This is the Samrat Yantra, which consists of two instruments. The outer arcs form a sextant, the Shashtamasa Yantra. Each arc’s a graduated 60º arc, with a dark chamber at the top—the chamber has a pinhole through which sunlight enters, allowing observations. The more exciting part of the Samrat Yantra is the staircase, an inclined wall parallel to the earth’s axis. It’s a sundial, which, besides indicating time, shows the sun’s declination.

At either corner of the well that contains the Samrat Yantra are two concave hemispheres that together form the next instrument, the Jaiprakash Yantra. The hemispheres were marked with scales, including the signs of the zodiac. Cross wires stretched across each hemisphere from north to south and east to west; the wires’ shadows helped determine the sun’s position. The Jaiprakash Yantra was used for varied zodiac observations, such as measuring the azimuth and altitude of a celestial body.

The fourth instrument’s also divided into two structures, which resemble Rome’s Colosseum, though smaller! This is the Ram Yantra. Each structure consists of a circular wall surrounding a pillar, with `spokes’ from the pillar to the wall. The height of the walls and pillar are equal to the internal radius of the instrument, and the floor is divided into 30 sectors, each covering 6º. All three—walls, floor, and pillar—are marked with scales. The Ram Yantra’s used to measure the azimuth and altitude of a celestial body.

All somewhat confusing, but it makes sense if you’re visiting on a sunny day and see for yourself—preferably with a guide who can demonstrate how each instrument works. Jantar Mantar’s open from sunrise to sunset. Tickets cost Rs 100 per person.

This must be a unique set of erections built in a small tranquil spot in the city. We’d spotted an odd triangular building, similar to a massive child’s slide, from the top of the Wind Palace and had been mildly intrigued as to its functionality. I couldn’t even begin to guess.

Our guide proudly escorted us to Jantar Mantar or Jai Singh’s observatory. Jai Singh, who had an absolute obsession with astronomy and established a total of five observatories in his lifetime, started work on this observatory in 1728. Four have survived and Jaipur is allegedly by far the most comprehensive (it was restored to its former glory in 1901.

Sawai Jai Singh was the founder ruler of Jaipur and other than ruling, soldiering he had a keen interest in architecture and the movement of the planets. He ordered numerous weighty astronomy books to be translated into his native language and dispatched scholars from his court to meet up with astronomical experts throughout the world. Then he began to develop his architectural and astronomical masterpieces. Indeed they are so precisely built that they are still in use to this day and we were told that the giant sundial was effective to 2 seconds (better than my modern watch, but not as transportable).

Although we were looking at technically elaborate equipment you could be forgiven in thinking that you’d found your way into the centre of an exhibition of modern sculpture. The lines of the creation are organic and flow beautifully through the park. Indeed so technical were some of the explanations of the purpose of the structures that I preferred just to admire the artistic nature of the creation. But it’s not just about telling the time because the set of stone instruments help track the movement of the stars (in both the southern and northern hemi-spheres) and forecast eclipses. Radically Jai Singh’s research moved him away from the traditional use of brass in instrumentation to the controversial use of stone His belief was proved to be sound because these instruments are reputedly error free.

Having built this fine set of structure Jai Singh set about recording all his findings and these mighty tomes are still safely stored at the City Museum. It was unfortunate that the sun was not shining on the day of our visit so we did struggle to see the shadows cast on the instrumentation, but our guide did his best to point out the features and pointed out the dimmest of shadow on the giant sundial. We spent a good hour wandering around this enclosure. Were intrigued that the "stairway to heaven" sundial was not constructed until several smaller working models had been fully tried and tested. There’s a wooden model on display and of course the baby sundial is only a few metres away from the "big daddy."

There is a stunning view of the wind palace and the experience is strongly recommended. A unique piece of history.

In contrast with the rest of the old city, the Jantar Mantar has not been painted pink (or, indeed, terracotta), and the instruments are all clad in gold-coloured gypsum. Although the observatory was constructed in 1728 there is something very contemporary about the style. With little in the way of decorative adornment, the instruments, in keeping with their functional nature, are more reminiscent of modernist architecture and certainly contrast sharply with the neighbouring crenellated walls and towers of the City Palace.

The Jantar Mantar is one of five observatories built by Jai Singh and contains eighteen instruments, some of which provide astronomical observations, and others are for astrological purposes. The most impressive structure is the Samrat Yantra which is a sundial nearly 30m tall in the centre and has huge curved sides where the shadow of the sun falls giving a time reading that is accurate to within 2 seconds. There is a smaller version of this instrument in the observatory where, unlike the Samrat Yanta, the central stairway was open to the public. The Jai Prakash Yantra is my favourite instrument, partly because it's very photogenic and partly because it's hard to even make a guess at what it's used for. Two 4m-wide hemispheres of marble set into the ground with a small copper ring suspended above them, the shadows of which show the date, time and phase of the zodiac. It was used to determine auspicious days for important events and also to reconfirm readings taken by other specifically dedicted instruments in the observatory.

Behind these is the impressive Nadivalaya Yantra - an enormous instrument used to record the passage of the sun through the hemispheres. The readings taken from some of the instruments is taken from markings on metal plates. The metal used is an alloy of seven different materials that are least susceptible to expension and contraction, thus providing the most accurate readings possible. The name Jantar Mantar appears to have two different interpretations: the first meaning 'device' and 'calculation'. Personally, I prefer the inexactitude of the expression 'magical device', as I think the word 'magical' sums up the experience of a visit to the Jantar Mantar. (Photos courtesy of a friend, as I forgot my camera this time!)

And so he started building his instruments, and collected them in an observatory, which still can be visited. He created a clock, up to 3 minutes exact, based on the positioning of the sun, and a wide range of small constructions which help him to identify the stars at each moment of the year.

The site still looks rather futuristic. If you go there, make sure you have a good guide with you, because the instruments are not self-explaining at all.