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

290 BRAHMAGUPTA'S ASTRONOMY ITS HIGHLIGHT
astronomical Laṅkā, as it is about six degrees to the north of
equator. The astronomical Laṅkā is mentioned by Brahmagupta
in the beginning of his very first Chapter¹.
According to Brahmagupta all the four yugas of a Catur-
yuga or mahāyuga are not of the equal duration :
Kaliyuga is of 432,000 years. Dvāpara of 864,000 years,
Tretā of 1,296,000 years and Kṛtayuga of 1,728,000 years;
total of the four is 4,320,000 years. Āryabhaṭa regards
all yugas of equal duration, 1,080,000 years².
The Saka era, which is usually used in Indian astronomy
for the reckoning of years commenced 3179 years after the
beginning of Kaliyuga.
The number of lunar months in a yuga does not coincide
with the number of solar months. Thus we have the conception
of the Intercalary months : the number of intercalary months in
a yuga denotes the excess of the number of lunar months in a
yuga over the number of solar months in a yuga. Thus in a
yuga we have
Lunar months 53,433,336
Solar months 51,840,000
Intercalary months 1,593,336
Lunar days 1,603,000,080
Civil days 1,577,917,500
Omitted lunar days 25,082,580
The number of omitted lunar days in a yuga is equal to the
number of lunar days in a yuga minus the number of civil days
in a yuga.
(Cont. from page 289)
पश्चिमेकेतुमालाख्ये रोमकाख्या प्रकीर्तिता ।
उदक्सिद्धपुरी नाम कुरुवर्षे प्रतिष्ठिता ॥ --Sūrya. XII. 36-39

1. चैत्रसितादेरुदयाद्भानोर्दिनमासवर्षयुगकल्पाः ।
   सृष्ट्यादौ लंकायां समं प्रवृत्ता दिनेऽर्कस्य ॥ —BrSpSi. I. 4
2. युगदशभागो गुणितः कृतं चतुर्भिस्त्रिभिर्गुणस्त्रेता ।
   द्विगुणो द्वापरमेकेन संगुणः कलियुगं भवति ॥
   युगपादानायैभटश्चत्वारि समानि कृतयुगादीनि ।
   यदभिहितवान् न तेषां स्मृत्युक्तसमानमेकमपि ॥ —BrSpSi. I. 8-9