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

510 longitude of Lubdhaka (Sirius) 86° and its polar latitude is 40° south. Comm. Clear. The star Agastya is considered to be important in Indian literature because the heliacal rising and setting of Agastya are directed to be noted and in fact are being noted in every panchanga even today from times.immemorial. Even Kālidāsa alludes to this heliacal rising of Agastya as inaugurating the Sarat-kāla or autumn which was reiterated by Varaha Mihira in his Bṛhat-Saṁhitā under the verse “भगवति जलधरपक्ष्मक्षपाकरा- केंक्षणे कमलनाभे, उन्मीलयति तुरङ्गमकरिरथनीराजनं कुर्यात्” ie. when Lord Vishnu whose eyes are supposed to be the Sun and the Moon and his eyelids the clouds, opens his eyes ie. on Kārtica Ekādasi the 11th day of the bright half of the lunar month of Kārtica then Kings are directed to perform Nīrājanavidhi for his horses, elephants and chariots (to start on an expedition for war). It is to be noted that this was so long ago in times of yore that Agastya used to rise at the beginning of autum. Now the star is rising about 22nd August long in advance even in the rainy season. This is on account of the effect of precession of equinoxes. Verse 8. The Iṣṭanādis for Agastya are said to be two, for Lubdhaka 2⅙, for other stars which are next in size, 2⅓ and for still smaller ones the Iṣṭanādis are to be taken still more. Comm. Iṣṭanādis ie. the time in nādis (where a nādi is equal to 24′ of time) giving the time in between the rising moments of the star and the Sun, when the star rises heliacally. In other words, let the star Agastya rise at a particular time t. If the Sun rises at t+48′, then it is the time for Agastya to rise heliacally. This again means that if the Sun sets at time T and the star at T+48′ in its diurnal motion, it is time for the star to set heliacally in the west. Similarly for the other stars. It will be noted here that stars set heliacally in the west and rise