सिद्धान्तदर्पण (महामहोपाध्याय सामन्त चन्द्रशेखर सिंह - नग्न-नेत्र खगोल वेध एवं गणित महाकोश)

liv सिद्धान्त दर्पण
Assuming then, that the zodiac at present in
use was fixed in Saka 427, let us explain a few facts
connected with it. First of all, we find that in 1389
years, which have elapsed since the date general
precession has amounted to 19°-23′-7″; while, had
the Surya-Siddhanta's year been in use throughout
the Sun must have been in error by 3°-15′-30″, thus
making the ayanamsa 22°-38′-37″ in Saka 1816 last.
The amount, however, differs from the observed by
28′,- a quantity too large to be neglected. On the
other hand, if Ganesa's length of the year be taken,
the error in the Sun amounts to 2°-9′-54″, making
the ayanamsa actually less by nearly 38′. It is
remarkable that the length of the year assumed by
Bhaskara makes the total 22°-12′21″, nearly the same
as is observed.¹
From the observed ayanamsa and the fact of its
commencement in Saka 427, the precessional rate
becomes 57″.45. This is lower than that obtained by
us from the Surya-Sidhanta's year, but nearly the
same as we obtained from Siromani's year. This
discrepancy between the rate calculated from
Surya-Siddhant and that found above can be
explained by supposing that the Surya-Siddhanta's
year may not have been in use throughout the large
interval of 1389 years, and that the rate of precession
is not known so acurately as may be sufficient for
the great length of time. The fact of Varaha's Surya-
Siddhanta giving a slightly shorter year (as shown
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1. The formula 50-2411 t+0001134 t² is adopted for
   calculating the general precession. See Chauvenet's
   Astronomy. The precession constant appears to be a little
   too large, as is remarked by the author. A calculation
   made from Bessel's constant allowing for its variation,
   renders the general precession nearly 1′ less.