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