VEDĀNGA JYOTISHA The earliest astronomical text from India, the Vedānga Jyotisha is attributed to Lagadha and has an internal date of approximately 1350 b.c. It is available in two recensions, one belonging to the Rig Veda and the other to the Yajur Veda (which, from the language used, appears to have been edited a few centuries later). The text is dated from the statement that the winter solstice was at the beginning of the asterism Shravishthā (beta Delphini) and the summer solstice at the midpoint of Ashleshā.
According to the Vedānga Jyotisha, in a yuga there are 5 solar years, 67 lunar sidereal cycles, 1,830 days, 1,835 sidereal days, 62 synodic months, 1,860 tithis, 135 solar nakshatras, 1,809 lunar nakshatras, and 1,768 risings of the moon. It also provides ingenious rules to determine the positions of the nakshatras, the sun, and the moon at any time.
A lunar month is divided into 30 tithis. The solar day is divided into 124 parts and also into 603 kalās. The measurement of time, by the use of a clepsydra, was in the unit of nādikā, which was the sixtieth part of a day. The units used were chosen to allow for the use of integers in various calculations.
The Vedānga Jyotisha is a lunisolar system in which the movements of the moon across the nakshatras in the sky identify the days, and the position of the sun, tracked by its northward and southward course in the two halves of year (ayana), identifies the twelve months of the year. In this system, intercalary months need to be added and other corrections made in order to make the sun's northward course begin in the correct month.
Although the Vedānga Jyotisha says that the yuga of five years has 1,830 civil days and 62 lunar synodic months, actually the correct number of days is 1,826, and an additional day should be added to the 62 synodic months. The length of the year was measured from one winter solstice to another, and this was taken to be 366 days. Since the year was divided into six equal seasons of 61 days, the civil count of 1,830 was a convention. The number of civil days in the yuga was corrected in the two extra intercalary months that were employed.
Lagadha gives the ratio of the longest to the shortest day as 3:2. This is true for northwestern India, and one may conclude that he belonged to that region.
Kak, Subhash. "The Astronomy of the Age of Geometric Altars." Quarterly Journal of the Royal Astronomical Society 36 (1995): 385–395.
Sastry, T. S. Kuppanna. Vedānga Jyotisa of Lagadha. New Delhi: Indian National Science Academy, 1985.