सिद्धान्तशिरोमणि: गणिताध्याय (भास्कराचार्य - ग्रहगणित, मध्यमाधिकार व स्पष्टाधिकार सटीक)

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longitude. Let rA, AB, BC, CD, DF be the successive
Sāyana Rāśis called Sāyana Meṣa, Sāyana Vṛṣabha etc.
(The Nirayana Rāśis also starting
from the Hindu zero-point are called
Nirayana Meṣa, Nirayana Vṛṣabha
etc. and if in Hindu Astronomy
we use the words simply as Meṣa,
Vṛṣabha etc. especially in panch-
āngas ie. the Hindu almanacs, we
have to construe them as belong-
ing to the Nirayana or the Hindu
system whose zero-point is called
Fig. 30
the first point of the constellation Aswini and not r).
rL = rD + DL = an integral number of Rāśis, say, ‘n’
of them ie. n × 30° + DL, where DL is the arc of the
Rāśi carrying the Lagna L. The question then resolves
itself into knowing how many Rāśis precede ‘D’ from r
and what the measure of DL is. The data are (1) the
Nirayana longitude of the Sun as computed by the
methods of Hindu astronomy (2) The Ayanamsa of the
year ie. ‘ro’ where o is the Hindu zero-point of the ecliptic.
(3) The time after Sun-rise at the place, given in Sāvana
units at which we are required to find the Lagna.
Finding the Lagna at a given point of time at a
given place is not only necessary in astronomy but its
importance is more in what is called horary astrology
or Muhūrta Sāstra, whose purpose is to fix an auspicious
moment for the performance of marriages etc. as well as
in astrology in casting a horoscope.
The finding of the rising times of the various Rāśis
at the equator, as well as at a given place was dealt with
in the previous chapter. Those rising times are found in
sidereal units, a sidereal day being divided into 60 nādis,
or 60 × 60 Vinādis or 60 × 60 × 6 asus. These units
are of constant magnitude since a sidereal day, which is
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