Bharatiya Jyotihshastra (History of Indian Astronomy), translated by R. V. Vaidya v1.c5.53

v1.c5.53

The moon becomes full after 29 or 30 days, and it becomes full again and again after the same number of days. The primitive man must have adopted the day (i.e. a day and night together) as the natural unit of time, after observing that the period between two successive sunrises is almost the same. Similarly, after observing the rule about the full moon stated above, he must have adopted the period between the consecutive full moons as the second but a longer unit of measuring time. This period seems to have received the same term as that given to the moon in many languages. In the Vedic literature, the moon is named as *māsa*. As an example the following lines may be seen :—