History of Dharmashastra (Ancient and Mediaeval Religious and Civil Law in India) v6.c82.631.1

v6.c82.631.1

Among all nations the fundamental periods of time are the same, viz. the day, the month and the year (consisting of seasons). The years are the constituents of eras that are vital for chronology and history. Though the fundamental periods of time are the same, there are variations in the arrangement of days to form months and years, about the sub-divisions of the day, about the commencement of the day, about the divisions of the year among seasons and months, about the number of days in each month and in the year and about various kinds of months. The great time measurers are the Sun and the Moon. The day is due to the revolution of the earth round its axis. The month is mainly a lunar phenomenon and the year is due to the apparent motion of the Sun (but in reality it is due to the revolution of the earth round the sun). The tropical year is the time of the passage of the Sun from one vernal equinox to the next. The latter is shorter than the sidereal year (i. e. the time between the two successive arrivals of the Sun at the same fixed star) by about 20 minutes as the vernal equinox point shifts to the west at the rate of about 50 seconds per year.⁹⁸⁷ A modern calendar mentions the current year (by some era), the month and the day of the month and generally the week-day, besides several other matters of religious and social interest. The eras and accurate knowledge of the length of the year and the month came to man rather late.