390 michio yano
These numbers are good enough to prepare a calendar. This is why there still
survive some traditional calendars which are based on the Su ̄ ryasiddha ̄ntaand
which give almost the same results as my computer program mentioned above.
Kali yuga epoch Since the mean positions of the Sun and Moon and the planets
are the function of time, one should assume a certain time as the initial point of
calculation. The class of astronomical literature called karan.ais characterized by
the use of an epoch which is not very far back from the time of the text, while
thesiddha ̄ntatexts employed an epoch in a very remote past where all the planets
were assumed to be in mean conjunction at the starting point of the ecliptic
coordinates. The epoch was sought by means of indeterminate equations of the
first degree – at a certain time true positions were observed and they were con-
verted into mean positions, while the mean motions of all the planets had been
somehow known. The epoch arrived at by this method was midnight of Febru-
ary 17/18 in 3102 bcaccording to the midnight (a ̄rdhara ̄trika) school, and the
sunrise of February 18 (Friday) of the same year according to the sunrise
(audayika) school. That the epoch was very accurately chosen can be demon-
strated by the fact that even today we can get a fairly good calendar using this
epoch and the constants of the siddha ̄ntatexts.
Planetary theory The numbers for the rotations of planets are also given in
astronomical texts. They vary slightly according to the schools (Pingree 1981:
15). Let us give here (table 18.4) those from the later Su ̄ ryasiddha ̄nta.
solar year = 365.258757,synodic month =D
Y
D
M==29 530588..Table 18.4Rotations in a Maha ̄ yuga
Fixed stars 1,582,237,828
Saturn 146,580
Jupiter 364,212
Mars 2,296,832
Sun 4,320,000
Ve n u s ’ ss ́ı ̄ghra 7,022,364
Mercury’ss ́ı ̄ghra 17,937,076
Moon 57,753,336
Moon’s apogee 488,203
Moon’s node -232,246