City of Isfahan has been situated in the center of Iran in 32? 40? north latitude, 51? 40? east longitudes. Naghsh-e-Jahan square sited in heart of historical city Isfahan. It has 4 great and splendid monuments in its 4 sides which all consider as great architectural heritage of Iran. In west side there is entrance of "Alighapoo" palace; in east Sheikh Lotfolah Mosque; in south Imam Mosque (Shah Abbasi) and in north side entrance of Kaiser Bazar of Isfahan has been placed. Imam mosque has been built is Shah Abbas era and it has been told that the mosque has been designed by Sheikh Bahai'l who was one of the famous philosophers and scientists of mentioned period. In west yard of Imam Mosque, a stone block has been installed next to northern wall that through all days of year (365 days) shows noon time without shadow. That is exactly when crier calls people to pray. This clock stone consists of two parts: a rectangular shaped stone and triangular shaped stone which together form an orthogonal trapeze. In midday, sunlight shines to southwest body with 125 degree angle and tangent northwest body.Imam Mosque turns 45 degree toward southeast in order to be in direction of kiblah; that is while Naghsh-e-Jahan square has 14 to 17 degree turn to south east to adapt with ray of sun light. Imam Mosque and Sheikh Lotfolah Mosque reflected incredibly. This wonder also exists in clock stone which has been adjusted and installed by Sheikh Bahai'l. Clock stone of Imam Mosque demonstrate reflection of two angles of mosque toward kiblan (southwest) and square toward south east. The secret of this stone is not only in the vector of sun light but also in way of shadow coverage by triangular shape stone which is surveyed and discussed in this research.
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