बृहत्संहिता (आचार्य वराहमिहिर - स्थापत्य, खगोल, मौसम व जल विज्ञान)

8 बृहत्संहितायाम् [Adh. II. 5-7
५. चतुर्णां च मानानां सौरसावननाक्षत्रचान्द्राणामधिमास-
कावमसंभवस्य च कारणाभिज्ञः ।
5. He should also be familiar with the four kinds
of measurements of time, viz., सौर.solar ; सावन, a duration
(day) intervening between the first rising of any
particular planet or star and its corresponding next
rising ; नाक्षत्र stellar calculation in terms of lunar months,
Tithis, etc., with the occurrence of Adhimasa or inter-
calary lunations and intercalary days.
A सौर day is the interval between one sun-rise and the
succeeding one. A सावन or terrestrial day is the interval between
two contiguous risings of the Sun at the Equator. Thirty such
days constitute a सावन month, नाक्षत्रदिन is the time taken by the
Moon to clear a Star. A चान्द्रमास consists of 30 lunar Tithis and is
a period intervening between two successive conjunctions of the
Moon with the Sun. An Adhika Masa is a period of a lunar
month occurring between two solar Sankramanas in the same
Rasi. For this and अवम, see Suryasiddhanta.
६. षष्ट्यब्दयुगवर्षमासदिनहोराधिपतीनां प्रतिपत्तिच्छेदवित्।
6. He should be familiar with the computation of
the commencement and termination times of the 60
year-period, the Yuga (5 year-period), a year, a month,
a day, an hour and also of their respective lords.
There are 12 Yugas or five-year periods in a cycle of
60 years and their lords are stated as follows :
विष्णुः सुरेज्यो बलभिद्धुताशस्त्वष्टोत्तरप्रोष्ठपदाधिपश्च ।
क्रमाद्युगेशाः पितृविश्वसोमशक्रानलाख्याश्विभगाः प्रदिष्टाः ॥
७. सौरादीनां च मानानामसदृशसदृशयोग्यायोग्यत्वप्रति-
पादनपटुः ।