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The lengths of the months given by the Surya are also wrong compared to their modern values. |
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The ingress of the Sun into a zodiacal sign is known as samkranti. This can occur at any time, but in practice, the civil month starts at sunrise. Hence, there is a need for a rule determining the start of the civil month in relation to the astronomical start. Not surprisingly, India has four such conventions, used in different states. |
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The consequence of the differing conventions regarding the start of the month, combined with the incorrect month lengths of the Surya, is the creation of several problems: |
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The civil day of the first of a month may vary by one to two days in different parts of India. |
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The integral number of days of various solar months vary from 29 to 32. |
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The length of the month is not fixed in terms of integral civil days but varies by year. |
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There are a number of other problems with the Surya, but the above discussion should suffice as a general introduction. |
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The Siddhanta system is the one used by the traditional calendar makers of India. Because it is out of date, it presents a variety of problems. Because the traditional calendars have a degree of religious sanction, they are difficult to change or eliminate. Because there are so many variants, they create conflicts for the planning of days of observance. |
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Otto Neugebauer, in an interesting paper (Osiris, volume 10, 1952, pp. 252276), investigated an earlier work by Warren (1825) which described the methods by which a Tamil "Kalendar maker residing in Pondicherry" was able to compute the circumstances of the lunar eclipse of 31 May 1825 by resorting solely to shells placed on the ground and memorized tables. A continuous tradition can be traced from third century B.C. Seleucid cuneiform tablets through third century Rome to the sixth century tradition of Varahamihira and thence via the Siddhantas and oral tradition to the 19th century. Once spread through an area as oral tradition, knowledge becomes very resistant to change. |
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In summary, many of the problems associated with traditional calendars in India can be traced to two sources: |
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Ossification by religious injunction. Change has been refused, even when its necessity has been established. |
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Lack of a reliable time base. Much of the inaccuracy of traditional Indian calendars stems from the choice of the Moon as a basis for timing. Lunar motion is extremely complex, and its apparent motion is highly variable. Indian astronomy erected very complex structures on the shifting sands of lunar motion. The complexity of the system obscured the errors. |
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