"Jaam-e jamshid", is an astronomical instrument through which we can plot the stars out and keep track of some astronomical events. Since astrology was of great significance to the ancients, in historical manuscripts, “Jaam-e jamshid” has been cited as a globe which represented the universe status. Moreover, it can be traced in the Persian epic book, “Shahnameh”, in which the history of the “Jaam” dates back to more than 1000 years ago. This astonishing astronomical object has been forgotten for a long time and there is no model of it left. Based on some written documents, the “Jaam” is supposed to be a hollow hemisphere with a vertical gnomon in the center. Some of the calculations which can be done by means of the gnomon’s shadow are as follows:

1. True solar time(as a sun dial)
2. Date of solar tropical year
3. The beginning of equinoxes and solstices
4. Prediction of the time of sun rise and sun set
5. The time of local noon that is important for Moslems as it is the time to pray.
6. Altitude and azimuth of the sun and the moon

In this project, the "Jaam-e jamshid" was successfully built and for the first time its function and application was studied in details scientifically. The current apparatus has the diameter of 120 cm and we believe it is the biggest model of it in the history. For using the device one should suppose the sky above as part of a celestial sphere on which all the celestial objects have been laid and then one should imagine his upper-head celestial sphere as if it is in the “Jaam” at the moment.

In addition to the application that it serves, today it can be used as an instructional instrument for teaching spherical astronomy and different coordinate systems.

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