ब्राह्मस्फुटसिद्धान्त (ब्रह्मगुप्त - शून्य, कुट्टक, बीजगणित एवं सम्पूर्ण २१ अध्याय सान्वय सटीक)

60 BRAHMASPHUṬA SIDDHĀNTA & KHAṆḌAKHĀDYAKA
treatise (i.e. Khaṇḍakhādyaka, literally meaning food
prepared from sugar-candy) is made so as to yield the
same results as that.¹
The mean saturn diminished by 3 seconds, the Śīghrocca
of Mercury diminished by 22 seconds, the mean Mars
increased by 2 seconds and the mean Jupiter increased
by 4 seconds are equal to the respective mean planets
of Āryabhaṭa's midnight system.²
In the Brāhmasphuṭasiddhānta, Brahmagupta accepts the
astronomical day to begin with the sunrise at Laṅkā, and the
calculations of days, months, years, Yugas, and Kalpas all begin
from Caitra Śukla Pratipadā (the first tithi of the month Caitra
in the bright-half of the Moon) and the first day is regarded as
Sunday.³
Varāhamihira in his epicyclic cast to the Sūryasiddhānta
in his Pañcasiddhāntikā adopts the ardharātrika system or the
system of reckoning days from midnight. The question why
Brahmagupta who was so bitter an opponent of Āryabhaṭa I
in his younger days (628 A.D.) claimbed down to describe and
teach one of the systems of Āryabhaṭa's astronomy in his sixty-
seventh year (665 A.D.) is difficult to explain. In fact so great
was Āryabhaṭa's reputation and fame that in spite of Brahma-
gupta's severe ricticisms of the former in Chapter XI of the
Brāhmasphuṭasiddhānta, it perhaps was undiminished and it
was Āryabhaṭa who continued to be universally followed.
Some authorities have thus expressed the view that to meet
the popular demand Brahmagupta in the Khaṇḍakhādyaka took
upon himself the task of simplifying Āryabhaṭa's ardharātrika
system and in this task he became eminently successful. But it
has been supposed that in this task he could not be a mere
simplifier or expounder.
प्रायेणार्यभटेन व्यवहारः प्रतिदिनं यतोऽशक्यः ।
उद्वाहजातकादिषु तत्समफल लघूक्तरोक्ति रतः ॥
तिसृभिः शनिज्ञैशीघ्रं द्वाविंशत्या कुजोऽधिको द्वाभ्याम् ।
चतसृभिरधिको जीवोऽर्द्धरात्रिकार्य्यभट मध्य समाः ॥
—KK. I. 1,2,7
☛ चैत्रसितादेरुदयाद्भानोर्दिनमासवर्षयुगकल्पाः ।
सृष्ट्यादौ लंकायां समं प्रवृत्तः दिनेऽर्कस्य ॥
—BrSpSi I.4