The Jantar Mantar in Jaipur is the largest and best preserved of five observatories built by Jai Singh throughout northern India. It contains 13 different instruments for calculating such things as the time of day, the altitudes of heavenly bodies, and the positions of constellations. Although the instruments look like modern sculpture, they are able to make calculations accurate to one second.
Raja Jai Singh had a deep interest in astronomy. He read all the known works on the subject at the time (c1800's). He also collected the most advanced instruments he could find. During his studies, he noted inaccuracies in existing astronomical tables and decided to produce his own astronomical instruments. Because he felt that the instruments' size limited their accuracy (they were too small), his solution was to build gigantic instruments from stone, masonry, and marble rather than the traditional brass.
Today, the instruments are still used to forecast such things as how hot the summer months will be, the expected date of arrival, duration, and intensity of the monsoon, and the possibility of flood or famine.

Some of the instruments pictured on this page are:
The Samrat Yantra: a 89 foot high and 148 foot wide sundial. When the sun moves across the sky, it casts a shadow on finely calibrated arms extending on either side. It measures local time, zenith distances, meridian pass times, and the declination of the stars. It is used to forecast the crop prospects for the year.
The smaller Laghu Samrat Yantra is not as accurate as the Samrat Yantra. However, it calculates Jaipur's local time to an accuracy of 20 seconds.
The Jaiprakash Yantra: the last instrument installed in the observatory, it consists of two marble bowls. This instrument aids in celestial observations and verifies calculations of other instruments in the observatory.
The Rashi Yantras: a collection of twelve instruments, each representing one of the twelve zodiac signs. Therefore, each instrument faces a different angle and constellation. It is used by astrologers to make accurate horoscopes.

Click on the links below to see a larger view of each photograph.