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

LUNAR ECLIPSES
Verse 1. The ritualistic purpose served at the time
of an eclipse.
Scholars of Smṛtis and pūrāṇas declare that prayer,
charity or offerings to gods made in fire at the moment of
an eclipse conduce to much spirituality. Hence I give
hereunder the methods of computing the moment of an
eclipse (lunar or solar) in as much as such a knowledge
apart from its religious importance, is also wrought with a
beautiful mathematical treatment.
Verse 2. The initial procedure to be adopted to
compute an eclipse.
To know the occurence of a solar eclipse, find the
exact moment of the New Moon, which is indicated by the
equality of longitudes of the Sun and the Moon, and to
know the occurence of a lunar eclipse compute the exact
moment of the full Moon which is indicated by the fact
that M = S + 180° where M and S are the longitudes of
the Moon and the Sun, agreeing in degrees, minutes and
seconds, though differing in Rasis by six. Also compute
the longitude of the Node (Rāhu) for the moment as
directed.
Comm. Having ascertained the possibility for the
occurence of a solar eclipse, we are directed to compute
the positions of the Sun, the Moon and Rāhu for the day
of the New Moon. The Sun and the Moon are to be
rectified for corrections like Desāntara, Bhujāntara,
Udayāntara etc. From the elongation of the Moon the
tithi is to be computed and the method of successive
approximations called Chālana Karma is to be used to
obtain the exact moment of conjunction. This process of