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