From altar astronomy to classical astronomy:

Classical Indian astronomy arose after the close interaction between the Indians and the Greeks subsequent to the invasion of the borders of India by Alexander the Great (323 B.C.). The existence of an independent tradition of observation of planets and a theory thereof as shown by geometric altars,
the Rigvedic code, and the VJ helps explain the puzzle why classical Indian astronomy uses many constants that are different from that of the Greeks.
This confirms the thesis that although classical Indian astronomy developed in knowledge of certain Greek works, the reason why it retained its characteristic form was because it was based on an independent, old tradition.
The astronomy of the third and the second millennium B.C. can provide the context in which the developments of Babylonian, Chinese, Greek, and the later Indian astronomy can be examined. It appears that certain features of the earliest Babylonian astronomy can be derived from an altar astronomy
that may have been widely known in the ancient world, but whose records are now available only in the Indian texts.
It also raises the question of an analysis of the altars and monuments from Babylon, Greece, and Rome to examine their designs. Likewise, the references in the Greek literature to geometric problems related to areas
need to be investigated further for their astronomical significance.
Later religious architecture, both in the east and the west, became more abstract but its astronomical inspiration was never hidden. In Europe cathedrals were a representation of the vault of heavens. In India the temple architecture, as spelt out in the manuals of the first centuries A.D. (see, for
example, Kramrisch 1946), symbolizes the sky where in addition to equivalence by number or area, equivalence by category was considered. The temple platform was divided into 64 or 81 squares (Figure 2). In the case of the 64- squared platform, the outer 28 squares represented the 28 lunar mansions of
the Indic astronomy. For the 81-squared platform, the outer 32 squares were taken to represent the lunar mansions and the four planets who rule over the equinoxial and solstitial points. Stella Kramrisch, the renowned scholar of the Indian temple architecture, has also argued that another measure in the
temple was that of 25,920, the number of years in the period of the precession of the equinoxes. Whether the precessional figure was received by the Indians from the Greeks or obtained independently is not clear.

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