Bharatiya Jyotihshastra (History of Indian Astronomy), translated by R. V. Vaidya v2.c12.s5.16
Bhāratīya Jyotiḥśāstra (History of Indian Astronomy), translated by R. V. Vaidya v2.c12.s5.16
- Language
- English
v2.c12.s5.16.1
Prepare an exactly circular ring**. It should be so tied at two points to the pole stick that it will be divided by those points into two exact parts. A second ring of the same size should be tied to the stick, so that it will cut the stick in those two points, will be perpendicular to (the plane of) the first ring, and will itself be bisected at the two points. These circular rings are called the pair of “standard great circles”. Tie a third ring to these rings at four points so that it will be at right angles to them both, and the pole stick will be its axis. This ring is termed ‘Nāḍīvalaya or Viṣuvavṛtta’. Divide this ring into 60 equal parts to represent nāḍīs (or ghaṭikās). A circular ring of equal circumference, called ‘Krāntivṛtta’ or the ecliptic circle should be tied to the ‘equator-circle’ cutting it at two points and inclined to it at an angle of 24°. The Sun moves in this circle. It should be divided into 12 equal parts to represent the signs. If the ball representing the earth be supposed to be a planet other than the sun, ‘great’ circular rings should be tied to the ‘ecliptic-circle’ at angles equal to the inclinations of the orbital planes of the planets. These also should be marked to show the signs. Then circular rings showing diurnal circles should be tied to the ecliptic circle.
v2.c12.s5.16.2
While tying the circular rings, care should be taken to see that a portion of the stick is kept projecting and these ends should be passed into two tubes fixed in the celestial sphere whose construction is described later on. The ends of the polestick should point to the poles of the equator, so that the north end of the stick should be found to make an angle, equal to the latitude of the place, with the north pole of the equator lying in the celestial globe which is fixed clearly all round the ‘starry sphere’; and the ends of the pole stick should be so passed into tubes that, while the ‘khagoi’ (celestial sphere) would be kept fixed in position, the starry globe would freely rotate in it. The celestial globe should be so set as to envelope the starry globe. Its construction is as follows. Its circular rings should, of course, be larger in size than those of the starry globe. The ring representing the ‘samavṛtta’ (prime vertical) which passes through the zenith, nāḍir, and the east and west points, similarly the ring representing the meridian, as also the other rings representing the secondary directions—all these four rings should be of the same circumference. These should be tied to one another, so that each of them would pass above and below the others. The ring representing the plane of the horizon should be tied to them all, midway between them.
v2.c12.s5.16.3
The north pole should be set above the horizon at an altitude equal to that of the latitude and the south pole at an equal depression below it. Prepare a ring representing the ‘Unmaṇḍal’ (six o’clock circle) i.e. the great circle which would pass through the east-west points and both the poles which are points in the meridian circle to which the ends of the pole stick in the starry globe are directed. Then tie a ‘nāḍivalaya’ (celestial-equator-circle) which lies in the plane of the equator of the starry globe and which is larger in size. This should be graduated into ghaṭis. Then fixing nails at the points representing zenith and nāḍir, another ring should be so fixed in position that it would be free to rotate in a vertical plane with the two nails as the pivots. This is to be called a ‘dṛṅmaṇḍal’ (i.e. the vertical circle for observation). As this is to be rotated inside the celestial glove it should be somewhat smaller in size. A planet is to be observed after so rotating the vertical circle that the planet would be seen in the plane of the observation circle. This celestial globe should be so fitted around the ‘starry globe’ that the ends of the pole stick could be made to pass through the two tubes fitted on to it. Then after fixing two tubes in the ‘khagol’ from the outside, another globe called driggola should be fitted on; and all circular rings like those in the ‘khagol’ and ‘bhagol’ should be fixed on to it.
v2.c12.s5.16.4
This globe is to be constructed so as to enable one to have a proper understanding of the arcual lines like ‘agra’ (amplitude) ‘kujya’ (the radius of the earth) etc., which require the reference to two globes. The whole structure is now Called a ‘gola’ (i.e. a globe). (Our astronomers sometimes used the term “kṣetra”, to denote lines.)