making them all equal to one another, so that each should extend over 13° 20′ or 800 minutes of arc on the Ecliptic, by which means the constellations were made to agree more nearly with the moon's mean daily motion. As the actual time for a mean sidereal revolution in 27.3216 days, 27 was the nearest whole number of days suitable for the division of the Ecliptic. Moreover, it was a more convenient number than 28, for calculation, in reducing all their observations to a system.
The Hindus, unlike the ancient Chinese, had not the ambition of making a catalogue of all the stars which were visible to them. They had a more important object in view, namely, the study of the motions oi the sun, the moon, and the planets, and other astronomical phenomena, primarily for the purpose of computing time, and of constructing and perfecting their calendars. Such an object, they knew, could not be materially advanced by ascertaining merely the positions of stars fixed beyond, or outside the course of the moving celestial bodies; and they accordingly confined their attention to those stars which lay in the moon's path, immediately North or South of the Ecliptic—stars which are liable to be occultated by the moon, or which might occasionally be in conjunction with it and with the planets.
By thus confining attention to the stellar spaces in the vicinity of the Ecliptic, their system was rendered, in the main, independent of the use of astronomical instruments, and dependent mostly on calculation for the accuracy of their observations.
Hence the ancient Hindu astronomers chose a set of 27 principal stars, one for each of the 27 Lunar Constellations, in general the brightest star of the Asterism, and called it Yoga-tara, whilst the Asterism cluster was named the Nacshatra. The Yoga-tara was connected with the beginning, or first point, on the Ecliptic of the division representing the space of the Asterism by the small arc of apparent difference of longitude between them, this arc being called the Bhoga of the Asterism.
