Indian Chronology (Solar, Lunar and Planetary): A Practical Guide to the Interpretation and Verification of Tithis, Nakshatras, Horoscopes and other Indian Time-records, B.C. 1 to A.D. 2000 c6.3

c6.3

2. First Astronomical Constant.—The Moon's Synodical Month or Lunation.—The first astronomical constant we have to know in Hindu astronomy is the moon's synodical month of 29½ days. The exact length of this period, according to the *Sūrya Siddhānta*,* which we shall always follow, except when otherwise stated, is 29·530587946 days. The ancient Hindu astronomers purposely calculated this period to what we should now call nine places of decimals in order that there might be no error even after thousands of years. The period fixed by modern astronomy does not differ from the above in the first six decimal places, and as ·0000008, the actual difference, is 1/100 of a second, it follows that the difference between European and Indian astronomy in 5,000 years or 61,844 synodical months may amount to 4,260 seconds or a little over 1 hour and 11 minutes. We shall see, when we come to compute new moons, that, in practice, the difference between the European and the Indian computation of new moons is very much less. [*Vide* Sec. 118, Rule (3) *infra.*]