Constructed
wholly with stone and marble Jantar Mantar houses fourteen architectural
astronomical instruments and is one of the famous five astronomical
observatories built by Maharaja Sawai Jai Singh II. The name Jantar
Mantar is derived from the Sanskrit term Yantra Mantra meaning a device
and formulae. The observatory took nearly seven years to complete and
was built between 1728 and 1734 at the behest of Emperor Muhammad Shah
who commissioned Raja Sawai Jai Singh II to correct astronomical tables,
as it was known that the Raja was an excellent astronomer himself and
took keen interest in astronomy. The observatory was declared a National
Monument in the year 1948 and is visited by astronomy lovers and general
public alike. Jantar Mantar is a living proof of the interest of the people even 300 years ago in astronomy and the science of celestial bodies. The fourteen geometric instruments of Jantar Mantar can still be used for making astronomical observations. The concrete astronomical instruments calculate the time of the day, can predict eclipses, measure the height of the celestial bodies and predict the situation of the constellations. The Samrat Yantra or the Sundial is one of the biggest geometric devices of Jantar Mantar and even today gives us correct time. Some other astronomical instruments at the Jantar Mantar are the Ram Yantra and Jaiprakash Yantra.
It is believed that Maharaja Sawai Jai Singh II sent his envoys all around the world to collect the latest astronomical knowledge of the times to build his observatory. Located opposite the gate of the City palace the Jantar Mantar of Jaipur is world's biggest stone astronomical observatory which can be used till date. The Jantar Mantar is visited by innumerable visitors every year who are completely in awe of the observatory to be build in its times.