Eternal India Encyclopedia

Eternal India encyclopedia

A ncient Concepts , Sciences & Systems

the achievements of Indian astronomy and mathematics and the Caliphs of Baghdad employed Indian astronomers. Varahamihira, who was born in the last quarter of the 5th century AD and was a contemporary of Aryabhata, is the author of the Panchasiddhantika and five other works - Vivahapaatala, Brihajjataka, Laghujataka, Yatra and Brihatsamhita. The Panchasiddhantika is a work on astronomy. The other works are astrological treatises and deal with such subjects as in- dividual horoscopes and the effect of the movements of planets on human life. Although his astronomical knowledge was of no mean order he appears to have been more a compiler of astronomical knowledge and a historian than an astronomer of originality. Bhaskara I, the greatest exponent of Aryabhata's system of astronomy, lived in the 7th century AD and was bom in c. AD 600. He wrote three works — the Mahabhaskariya, the Laghubhas- kariya and a commentary on the Aryabhatiya. The Mahabhas- kariya is an elaborate exposition of the three astronomical chapters of the Aryabhatiya. Bhaskara I gave a new method to find the mean longitude of planets and explains the application to astronomy of the rules of determinate analysis expounded by Aryabhata. Bhahmagupta (c. 598 A.D.) a contemporary of Bhaskara I, was critical of the views of Aryabhata. He attacked him for upholding the rotatory motion of the earth and for abandoning the Rahu-Ketu theory of eclipses in favour of the explanation that eclipses were caused by the shadows of the moon and the earth. However, later in life he appears to have somewhat diluted his opposition to Aryabhata when he wrote his Khandakhadyaka based principally on Aryabhata's ardharatrika system. Brahmagupta's works popular- ised among the Arabs a new mathematics-based astronomy. His Khandakhadyaka and Brahmasphuta-Siddhanta were translated into Arabic. Jaina interest in astronomy began early. The Jaina priest had to possess knowledge of astronomy to decide the right time and place for religious ceremonies. The principal source of Jaina astronomy is Suryaprajnapti the authorship of which has been attributed to Ma- havira. Another important astronomer was Bhadrabahu (d. 298 B.C) who is believed to be the author of a commentary on the Suryaprajnapti and of an astronomical samhita known after his name. Jaina astronomy conceives of two suns, two moons and two sets of 27 nakshatras as a consequence of Jaina cosmography regarding the earth as a series of flat concentric rings of land massed separated by concentric ocean rings. Several types of simple astronomical instruments were in use among astronomers in ancient India and medieval times. The water clock was a vessel with a small orifice at the bottom, permitting water to flow out in a fixed unit of time. In course of time the water- flowing type was replaced by the sinking type in which a vessel with a hole was permitted to sink in a larger vessel containing water. The astrolabe began to be used in India during the medieval period. This versatile instrument was known to the Greeks. It was perfected by the Islamic astronomers in West Asia, Central Asia and Spain and travelled to India along with Arab astronomy. In the 18th century, Maharaja Sawai Jai Singh II of Jaipur erected huge observatories in Jaipur, Delhi, Ujjain and Mathura where the heavens could be observed with a variety of instruments. The observatories were called Jantar Mantar ('Mysterious instru-

Diagram of Samrat Yantra

ments'). They can still be used for determining the time of the day, rising signs of the zodiac etc. The masonry instruments built under Jai Singh's instructions to equip the observatories at Delhi, Jaipur, Ujjain, Banaras (Var- anasi) and Mathura include huge dials, azimuth instruments, me- ridian circles, sextant and several other variations of them. The Delhi observatory consists of four main instruments or yantras. They are — Samrat Yantra, Jai Prakash, Ram Yantra, Misra Yantra. Jai Singh actually measured the local time in addition to the various co-ordinates of celestial objects. He mainly dealt with the sun, the moon, the planets and some bright stars. The most important of the huge dials was the Samrat Yantra. The Samrat Yantra : It is also the largest and most impos- ing. Portions of it are below ground level. The structure is 20.7 m (68 ft) high, 38.1 m (125 ft) from east to west and 36.6 m (120 ft) from north to south. It is an equinoctial dial, consisting of a triangular gnomon with the hypotenuse parallel to the Earth's axis On either side of the gnomon is a quadrant of a circle parallel to the plane of the equator. It is, in principle, one of the simplest 'equal hour' sundials. In the Fig., AB is the edge of the gnomon and the angle ABC is the latitude of the place. EF and GH are at right angles to AB, as also are DF and MH. Thus EF, GH, DF and MH are all in the plane of the equator. Further, if KL is the direction of the Sun, then the shadow of the gnomon cast by the light of the Sun on the quadrant is at JK. Under these circumstances, the arc KG indicates apparent local solar time before noon, and the angle HGL gives the declina- tion of the Sun. Similarly, the eastern quadrant indicates the time after the Sun crosses the meridian. Each edge of the gnomon has two scales of tangents, one from H to B and the other from F to A. would be between A and H and the declination of the Sun would be the angle FEL 1 . However, on 21 March and 25 September of every year, F will cast its shadow on E, while H will cast its shadow on G, indicating that the Sun is in the plane of the equator. That is, its declination on these two dates would be 0°. In the mass of masonry work which supports the east quadrant, is a chamber that contains the Shashtamsa Yantra or the Sextant. It is a large graduated arc lying in the plane of the meridian and is built in a 'dark room'. A small orifice at the top of the building and exactly above the quadrant admits sunlight at noon, forming the image of the Sun on the graduated arc. The position of this image marks the Sun's meridian altitude with fair accuracy. From this, the declination of the Sun can also be directly deduced. If the Sun is north of the equator, then the position L 1