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The presumption by scholars is that Kaniska used a pre-existing era. This era would have been the old Saka era, which began in 123 B.C. Hence, year 1 of the Kaniska era is year 201 of the old Saka era, omitting the hundreds position. |
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A general history has been reconstructed for the Sakas, who emerged from central Asia to wrest Bactria from the Parthian empire. Judging from their coinage, the Saka rulers adopted Greek culture. The Sakas spread from their new base of Sakasthan in modern Afghanistan, and some pushed southward into India. These southern groups used the old Saka era and a method of recording dates that duplicates the Greco-Chaldean system used in Parthia at the time. Later, these southern Saka rulers adopted Indian month names. |
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The classical Saka era of A.D. 78 is, in this view, just the old Saka era of 123 B.C. with the hundreds position omitted. This era is important, because it is the one used by Indian astronomers for date calculation. Although over 30 eras are known in India, only the Saka era has been used by Indian astronomers for calendric calculation. |
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9.6.1.2.5
The Surya Siddhanta |
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The Vedanga Jyotisha calendar was used through the end of the reign of the Satavahanas (ca. A.D. 200). The Saka and Kushana rulers introduced the Greco-Chaldean methods of date recording in the period from 50 B.C. to A.D. 100, and this system was accepted by some purely Indian dynasts as early as A.D. 248. |
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The period of A.D. 4001200 is known as the Siddhanta Jyotisha period. Indian astronomical treatises are known generally as Siddhantas. The earliest Indian astronomer who can be securely dated is Aryabhata (A.D. 476523). |
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Varahamihira mentions in his work several Siddhanta, but of these, only the Surya Siddhanta has survived. This work is still venerated by Indian astrologers. The Surya was apparently subjected to revision and constant updates of the values of the astronomical constants, with the last update occurring in A.D. 1603. Consideration of certain stellar coordinates shows that the Surya might have used data collected about A.D. 280, when Citra (alpha Virginis) was close to the autumnal equinox point. |
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The Surya is a compendium of astronomical knowledge, which in its modern form has 500 verses arranged in 14 chapters, each of which is concerned with a particular subject, such as mean planetary motion (Chapter 1). It is a codification of the Greco-Chaldean system passed through Parthia to India. |
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A fair amount of history can be deduced from what the Surya says and does not say. The compilers of the Surya were not familiar with Ptolemy's Almagest, for example. Neither did they know about the precession of the equinoces or accept the theory of "trepidation" formulated by Theon of Alexandria (ca. A.D. 370). The compilers use a value for the length of the year that is slightly too long, 365.258756 days. This value is not found in foreign sources. The compilers accepted a geocentric theory of the solar system, and set the first point of Aries to be coincident with the vernal equinoctial point. |
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