Eternal India Encyclopedia

ncient Concepts

Sciences & Systems

Eternal India

encyclopedia

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.

If the Sun is north of the equator, then the position L

would be

between A and H and the declination of the Sun would be the angle

FEL

. 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.