The Jantar Mantar is a collection of architectural
astronomical instruments, built by Maharaja
- meaning King - Jai Singh II at his then new
capital of Jaipur between 1727 and 1734. It
is modelled after the one that he had built
for him at the then Mughal capital of Delhi.
He had constructed a total of five such labs
at different locations, including the ones at
Delhi and Jaipur. The Jaipur observatory is
the largest of these.
The observatory consists of fourteen major
geometric devices for measuring time, predicting
eclipses, tracking stars in their orbits, ascertaining
the declinations of planets, and determining
the celestial altitudes and related ephemerides.
Each is a fixed and 'focussed' tool. The Samrat
Jantar, the largest instrument, is 90 feet (27
m) high, its shadow carefully plotted to tell
the time of day. Its face is angled at 27 degrees,
the latitude of Jaipur. The Hindu chhatri (small
domed cupola) on top is used as a platform for
announcing eclipses and the arrival of monsoons.