The Astronomical Observatories of Jai Singh c15.s1.t2: Vedāṅga Astronomy
The Astronomical Observatories of Jai Singh c15.s1.t2
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Vedāṅga Astronomy
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66. (a) The Jyotisha Vedāṅga¹ and the Sūryaprajñapti contain the earliest formal astronomical statements. The former introduces the 5-year cycle of 1830 apparent solar days. The year was tropical in theory and contained 366 apparent solar days, and was, therefore, too long. The sidereal year was 367 sidereal days. The lunar day or tithi was 61/62 of an ordinary day, but was reckoned as equivalent to an ordinary day for calendar purposes, one tithi being omitted as occasion required. There were 27 nakshatras, each supposed to occupy 360/27 = 13 1/3 degrees of the ecliptic, and each nakshatra was considered to be divided into 124 equal divisions, or aṃśas. The sun, therefore, traversed 5 × 27 asterisms in the five-year cycle, or 5 × 27 × 124 / 1830 aṃśas a day; and to traverse one nakshatra it took 13 1/3 days = 13 days 335 kalās, since there are 603 kalās in one day. The moon traversed 67 × 27 / 1830 = 603/610 nakshatras in one day, and one nakshatra in 1 day 7 kalās.
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¹ Vedāṅga is the name of certain works, or classes of works, regarded as auxiliary to the Veda. They are generally considered as of a somewhat later date.
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The five-year cycle appears to have commenced with the winter solstice, and Śraviṣṭha is said to have marked the beginning of this cycle, and also the beginning of the sun's progress, and also the winter solstice—all of which are in agreement. If Śraviṣṭha is to be identified with β, α, γ and δ Delphini (as it usually is), then it marked the winter solstice about B.C. 1100. But a list of asterisms given in the text begins with Aśvini (β, and γ Arietis), which marked the vernal equinox about the beginning of the Christian era. The Vedāṅga states that, during the northern progress of the sun, the days increase in length at an even rate of 1·57 minutes a day, or 4 hours 48 minutes in six months of 183 days²: the northern and southern progress are considered equal.
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² The table of climates on page 131 shows that an increase of 4 1/2 hours corresponds to a latitude of 36° 38' N., the obliquity being taken as 23 1/2 degrees. For a greater obliquity it would be further north.
c15.s1.t2.5
(b) The Sūryaprajñapti is a Jain treatise on astronomy, that is similar in many respects to the Vedāṅga. The Jainas held the old Indian idea of the heavenly bodies revolving round Meru, and, as a corollary to this, they conceived two suns, two moons and two sets of constellations. The five-year cycle began with the summer solstice, with the sun in Pushya, and Thibaut thought³ this was a correction, from actual observation, of the older Vedāṅga.
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³ Thibaut calculates a precession of 17° 3', or a difference of 1246 years between the Vedāṅga and the Sūryaprajñapti, but gives a caution as to the uncertainty of the deduction.
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Another point of difference was the employment of 28 nakshatras of unequal extent, and this altered, theoretically, the positions of the nakshatras—in some cases to a very considerable extent, and makes our estimations of the periods in which these works were composed very uncertain.
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(c) The characteristics of this period are:—
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(1) The five-year cycle.
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(2) The division of the sphere into 27 or 28 nakshatras.
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(3) Equal daily change in the length of the day.
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(4) Omission of any explicit reference to the planets.
Linked texts (2)
- Ārcajyotiṣa — Lagadha, Sanskrit
- Sūriyapannatti — Ardhamāgadhī Prakrit