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

216
Again from these positions, let the tithi be computed and
again let the above process be carried out until a constant
time is arrived at for conjunction or opposition.
Comm. (1) The above procedure is accepted by
Bhaskara as Āgama enunciated by Brahmagupta and
reiterated by Chaturveda as giving results that accorded
with observation. We shall see that the correction known
in modern astronomy as 'correction due to astronomical
refraction' is indicated here, though it was not stated
explicitly.
In fact what was stated by Brahmagupta was that
the periphery of the Manda epicycle given as 13⅔° for the
Sun and as 31-36 for the Moon hold good only on the
meridian but the periphery of the Sun is to be increased
or decreased by 20' according as the equation of centre is
negative and the Sun is the Eastern equatorial horizon,
or western equatorial horizon. If the equation of centre
be positive the reverse correction is to be effected in
the periphery i.e. for negative equation of centre.
Periphery on the Eastern equatorial horizon = 14°-0
On the meridian = 13°-40'
On the Western equatorial horizon = 13°-20'
For positive equation of centre
Periphery on the Eastern unmandala i.e.
equatorial horizon = 13°-20'
On the meridian = 13°-40'
On the Western unmandala = 14°-0
In the case of the Moon, for negative equation of
centre.
On the Eastern unmandala = 30 - 44
On the meridian = 31 - 36
On the Western unmandala = 32 - 28