Jantar Mantar - The Stone Obsevatory
One of the oldest observatory know to an Indian astronomy student is
“Jantar Mantar”. King
“Svai Jai Singh” built this observatory in four
different cites of India-Delhi,Varanasi(Banaras),Jaipur,............. around 18th century.
These massive structures are built to perform serious astronomy observations, Delhi's observatory consists of four “
Yantras” namely -
Misra Yantra Samrat Yantra Jaiprakash Yantra Ram Yantra Most of us wrongly think that all of these instruments are made to calculate the local time but only two of the Yantras (Misra yantra & Samrat yantra) are actually meant for time measurements and other two are used to calculate the position of heavenly bodies in the
sky.
First of all these four yantras, as we enter, we will see the Misra Yantra, it was believed to be built not by Savi Jai Singh but by his grandson, it is mixture of three yantras and hence the name Misra.
It can be used to calculate the local time with the use of
Equatorial Sundial by measuring the
length of the shadow on two different quadrants of Misra Yantra at the different time of the day. Two central dials on both side of central Gnomon, the central stairs pointing directly to the North Pole (Polaris) and parallel to earth's rotational axis, is used to
measure declination angle of Sun and other heavenly bodies. Declination angle is measured in degrees and its a measure of how far up or below is the object from the equator. Last of the three Yantras that are part of Misra
Yantra and one of the least understood is Kark Rashi Valya, we do not understand the proper working of this yantra but with its tilt of 50 towards south should mark the time when Sun enters into Kark Rashi (Capricorn). And the elaborated
dial along the wall should make it a perfect local watch, with an accuracy of 2sec (expected), on the day of Summer Solstice - 21 march every year .
Second in the list is the piece of art – Samrat yantra. Its a huge equatorial sundial. The stairs in middle are called Gnomon, parallel to the Earth's rotational axis, and two circular quadrants in the plane of equator on the either side of the gnomon. The length of shadow on the two quadrants swept equal length in equal time and measurement of length of shadow will give the local time with an accuracy of 0.5 sec on any sunny day, we can also use this dial to measure declination angles of different celestial objects.
Next is jaiprakash yantra, it is a pair of two structures, each structure is complementary to the other. It is a replica of sky, and can be used to measure accurate position of different celestial objects in sky.
Last in the row is another pair of yantras – Ramyantra. It is the instrument which is strongly believed by most of the persons to be meant for time keeping but actually it is made to calculate the local co-ordinates of the heavenly bodies. Similar to Jaiprakash it's two structures are complementary to each other, if on one instrument the object or its shadow can not be seen on dial but in the gap of the dial then on the other instrument it will be on the dial and using both of them simultaneously we can measure the change in position of objects in sky for whole length of night with time.
We as a astronomy student should use these instruments, as they are very easy to use and give a realistic feel of the sky. As a student we can learn and appreciate various co-ordinate systems which are useful to locate the most wonderful and massive objects in sec.
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