"“… The passage [Śat. Br. II.1,2,3. …] in which we read that the Pleiades “do not swerve from the East” should probably not be interpreted as meaning that they rose “due east” (which would have been the case in the third millenary B.C., and would point to a knowledge of the vernal equinox): the correct interpretation is more likely that they remain visible in the eastern region for a considerable time – during several hours – every night, which was the case about 1100 B.C. [I am indebted for this explanation to Professor A. Prey, the astronomer of our University, who informed me that, in about 1100 B.C. the Pleiades rose approximately 13º to the north of the east point, approaching nearer and nearer the east line, and crossing it as late as 2 h 11 m after their rise, at a height of 29º, when seen from a place situated at 25º North latitude. They thus remain almost due east long enough to serve as a convenient basis for orientation. This interpretation of the passage is proved to be the correct one, by Baudhāyana-Śrautasūtra 27,5 (cf. W. Caland, Uber das rituelle Sūtra des Baudhāyana, Leipzig 1903, pp. 37 ff.), where it is prescribed that the supporting beams of a hut on the place of sacrifice shall face east, and that this direction shall be fixed after the Pleiades appear, as the latter “do not depart from the eastern region.” It is true that, about 2100 B.C. or about 3100 B.C., the Pleiades touched the east line earlier, but they proceeded southwards so rapidly that they were not suitable for orientation.] …”."