Jantar Mantar is a collection of architectural astronomical instruments. The Jai Prakash, two bowl shaped hemispherical dials, is considered to be Jai Singhs most complex and elaborate instrument. A taut crosswire suspended above the hemispheres holds a plate which serves as a sighting device for night observations, and casts a shadow for daytime observations. It has upon its surface engravings of equatorial coordinate systems used to describe the position of celestial objects