Surya Siddhanta
ऐन्दवस् तिथिभिस् तद्वत् सम्क्रान्त्या सौर उच्यते। मासैर् द्वादशभिर् वर्षम् दिव्यम् तद् अह उच्यते ॥
Thirty lunar days make a lunar days make a lunar month, and a solar month is the time which the Sun requires to move from one sign[1] of the Zodiac to the next. A solar year consists of twelve solar months; and this is called a day of the Gods.
english translation
aindavas tithibhis tadvat samkrAntyA saura ucyate। mAsair dvAdazabhir varSam divyam tad aha ucyate ॥
hk transliteration by Sanscript