Maharaja Sawai Jai Singh II was a learned man and an astronomer who was deeply interested in the workings of the celestial bodies and so built the Observatory.He used it daily, often with his astronomy gurus Pandit Jagannath and Kewal Ram.

The structure portrays noteworthy attempt of the ancestors, who were interested in astronomy and knowledge of celestial bodies. Above all, this observatory still, provides accurate information, which can be compared with today's modern instruments undeniably.

The structure with its striking combinations of geometric forms at large scale has captivated the attention of architects, artists, and art historians world wide, yet remain largely unknown to the general public.

In all there are 17 instruments in the Jantar Mantar complex. The function of each instrument is rather complex but serves a particular function where time plays the main theme. Some of the other functions are predicting eclipses, tracking stars in their orbits, ascertaining the declinations of planets, and determining the celestial altitudes and related ephemeredes.

The Samrat Yantar, the largest instrument, is a sundial that looks like a triangular structure and is marked with hours and minutes. It is used to tell the time to an accuracy of about two seconds in Jaipur local time. The sundial is 27.4m high and is still used on the Guru Purnima (full moon day in the month of Jul/Aug) to forecast the onset of monsoon. The Hindu chhatri (small domed cupola) on top is used as a platform for announcing eclipses and the arrival of monsoons.

Kranti Yantra used for direct measurement of the longitude and latitude of the celestial bodies.

The Diganta Yantra was deviced to measure the azimuth (arc of the celestial great circle from Zenith to horizon) of planetary bodies.

Similarly, the Small Ram Yantra and the Large Ram Yantra are used to find the altitude and the azimuth.

The Chakra Yantra gives the angular measurement of an object from the equator.

The Jai Prakash Yantra determines the precise coordinates of celestial bodies and the small iron plate strung between the crosswires gives the sun’s longitude and latitude and the zodiacal sign that it is passing through. Its main function is to keep an eye on all the other instruments.

The Rashivalayas Yantra operates in the same manner as that of the Samrat Yantra and has one sundial for each of the zodiac signs. Five of them (Gemini, Taurus, Cancer, Virgo and Leo) are at the back from north to south. Aries and Libra face them followed by Aquarius, Pisces, Capricorn, Scorpio and Sagittarius from north to south. It helps in taking readings the moment each zodiacal sign crosses the meridian.

The Dakshina Yantra is a wall is aligned along the north-south meridian. It is mainly used to observe the position and movement of the celestial bodies when they pass over the meridian.

The Disha Yantra has only one function and that is to point towards the north.

The Unnathamsa Yantra is used to find the altitudes of the astral bodies. Observations can be made round the clock and the sunken steps help in taking readings from any portion of the dial.

The Raj Yantra or the King of Instruments is used only once a year to calculate the Hindu calendar, the details of which are based on the Jaipur Standard. To do so a telescope is fixed over the central hole. A bar for sighting is then attached at the back of the instrument. The plain disk is used to record the sightings. The Observer’s Seat belonged to Maharaja Jai Singh and was used for observing the wonders of the sky and universe.

The Narivalya Yantra is a distinctive sundial with two dials - the first dial facing south reads time when the sun is in the southern hemisphere, i.e., from 21 September to 21 March and the other one facing north reads time for the rest of the year when the sun is in the northern hemisphere, i.e., from 21 March to 21 September.

The Dhruva Yantra is used to locate the position of 12 Zodiac signs and also the Pole Star at night. Traditionally, human breath, approximately of 6 secs was used as the standard unit of measurement.

Thoroughly restored in 1901, the Jantar Mantar was declared a national monument in 1948. So do not miss the opportunity to check out the biggest stone observatory in the world, which is still in a running condition and stands witness to the wisdom of the former age.

Jantar Mantar is opened for visitors from 9:30 AM till 4:30 PM.