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 c11: Chapter VI. Nakshatras
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 c11
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Chapter VI. Nakshatras
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35. The system of quoting dates by Nakshatras is as old as that of quoting by tithis and has prevailed in India from equally ancient times. There are twenty-seven nakshatras or lunar mansions through which the moon passes in her monthly journey through the stars. For purposes of astronomical computation, the moon is supposed to spend an equal amount of time in each of the 27 nakshatras; and as the total period of the moon's journey through the stars occupies 27·32166 days, it follows that the mean duration of each nakshatra is 27·32166/27 = 1·01191 days, i.e., 1 day and nearly 18 minutes. Thus, if we know the ending moment of a particular nakshatra, all we have to do to find out the ending moment of the next nakshatra, or, for that matter, of any other nakshatra, is to add as many times 1·0119 days as there are nakshatras between the ending moment which we know and the ending moment which we wish to find out. Having found this ending moment, we have next to add or subtract the moon's equation of time according to her anomaly at the ending moment of the nakshatra. We should remember that the sun's anomaly and the sun's equation of time do not enter into the calculation of the ending moment of nakshatras, because we are now concerned with the moon's own journey among the stars and not with the space gained by her over the sun.
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∗ That is, on the *amanta* system or the system of reckoning lunar months from New Moon to New Moon. There is also another system, prevalent in certain parts of India, of reckoning the lunar months from Full Moon to Full Moon, hence called the *purnimanta* system. On this system, which in all probability was more widely current formerly than it is now, the New Moon is at the middle of a lunar month and the two halves of each month are properly designated its *pakshas* or wings, one on either side of new moon. Also, the new moon at the end of the *amanta* Chaitra lunar month, for instance, would, on the *purnimanta* system, be properly called the "Vaisakha new moon." As explained elsewhere, it is sometimes a difficult question whether a lunar month, referred to in an inscription, is to be understood in the *amanta* or in the *purnimanta* sense. See Sections 107 to 111 *infra*.
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36. When all we wish to know is the nakshatra for a particular tithi we may ascertain this directly from the mean tithi. The mean tithi, as we know, gives us the moon's longitude minus the sun's longitude. If to any tithi, therefore, we add the sun's longitude, we shall get the moon's longitude and this will enable us to find the nakshatra corresponding to the longitude. The sun's longitude for nakshatras for every whole day of the solar year is given in the last column of the calendar (Table VIII); while the sun's longitude for decimals of a day is given in Table V. (The process of determining the sun's longitude for the purpose of nakshatras consists, briefly, in making 360° equal to 29·53059 day-spaces, and allowing for the sodhya of 2·1707 days. This conversion is necessary in order that we may add the moon's less the sun's longitude, which is calculated at the rate of 360° for 29·53059 days, to the sun's own longitude). To give an example, supposing we wish to find the nakshatra corresponding to the 27th day of February, A.D. 1910, which we found was the 18th tithi of lunar Māgha, ending at ·2487 of the day, after sunrise, we proceed to determine the sun's longitude for the nakshatra. From the tithi we know that the sun's longitude for solar anomaly for the tithi is 320·30 days. The corresponding sun's longitude for nakshatra is as follows:—
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For 320 days (according to Table VIII) 25·6960 days. For ·30 day (according to Table V) ·0242 " Add moon's less the sun's longitude, i.e., the equivalent of 18 tithis in days 17·7183 " 43·4385 Deduct the equivalent of 360° of the moon's longitude 29·5306 13·9079
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We look in Table III for the nakshatra equivalent of 13·9079 days in lunation space. We find this to be number 13, whose longitude extends from 13·12470 to 14·21843. Now, No. 13 nakshatra is called Hasta, which is therefore the nakshatra current at the ending moment of our tithi.
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37. When we wish to find the current nakshatra corresponding to a tithi, the above method may be varied by converting the tithi into degrees at the rate of 12° for each tithi and adding the sun's longitude from Table XVII A and C, as in the example in Sec. 287.
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38. When we wish to find the ending moment of a nakshatra, the following method is preferable. This method, which is very simple, is indicated in Table XI which is provided in ghaṭikas and palas as well as in decimals of a day. To use this table, we should know the number of the nakshatra and the number of the new moon which the nakshatra follows, i.e., whether it is the 1st, 2nd, 3rd, or 4th new moon, and so on, and then under the new moon in question we look out the "interval" opposite the number of the given nakshatra. The next step is to deduct from the interval so found the equivalent (according to the Correction Table in Table XI) of the time of occurrence of the first new moon in the Solar Year (given in Table X). The result, added to the date of the New Moon, gives us the mean ending moment of the nakshatra. If we wish to have the absolute ending moment, we take the equation for the nakshatra (Table IX j to l) corresponding to the moon's anomaly, and if we wish further to have the absolute ending moment in local time, we add or subtract the corrections according to Table XIII for the given latitude and longitude.
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39. Suppose we want the ending moment of Nakshatra Mūla in Lunar Kārttika A.D. 1910, we proceed as follows :—
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| | Days. | ☾'s Anomaly Days. |
| First New Moon in Solar Year (Table X) ... | 25·9134 | 0·535 |
| Add for Kārttika New Moon ( " ) ... | 177·1835 | 11·856 |
| Add commencement of Solar Year ( " ) ... | April 13·2080 | |
| Days from April 1 A.D. 1909 ... | 216·3049 | |
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"Interval" corresponding to No. 19 "Mūla" Nakshatra under Kārttika (No. 7 New Moon)—Table XI ... ... 6·1353
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Deduct equivalent of 25·9134 according to the correction table in Table XI.
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| | Days. | | | |
| Equivalent of 25 = 1·8700 | | | | |
| " 91 = ·0681 | | | | |
| " ·0034 = ·0002 | | | | |
| 25·9134 = 1·9383 | — 1·9383 | | | |
| | | + 4·1970 | + 4·1970 | + 4·197 |
| Days from April 1 ... | 220·5019 | 16·588 | | |
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Nakshatra equation (Table IX-k) for anomaly of 16·588 days is + ·2465 ... ... + ·2465
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220·7484 days from Ap. 1.
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That is (by Tables VIII and XIX) 44 ghaṭikas 54 palas after mean sunrise on 6th November, A.D. 1910.
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N.B.—For the years A.D. 1840 to A.D. 1919 we can get the ending moment of any Nakshatra yet more quickly from Tables XI and XII in the following manner:—
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| | days | gh. | palas. | | d. | gh. | p. |
| (Table XII) Kārttika New Moon 1910, November | 2 | 18 | 18 | ('s Anom. | 12 | 23 | 28 |
| Nak. interval No. 19 (Table XI—A, col. VII) | | 6 | 8 | 7 | | | | |
| Deduct for Nak. 1910-11 (Table XII, last col.) | | -1 | 56 | 18 | | | | |
| | | 4 | 11 | 49 | 4 | 11 | 49 | | 4 | 11 | 49 |
| Nak. Equation for ('s Anom. of 16 d. 35 gh. 17 p. (Table IX-/) | | | | | + | 6 | 30 | 7 | 16 | 35 | 17 |
| | | | | | | 14 | 50 | | | | |
| | | | | | | 6 | 44 | 57 | | | | |
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The ending moment is Nov. 6, 44 ghaṭikas 57 palas after Ujain sunrise, which only differs by 3 palas from the result above arrived at.
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42. If we want this in local time, say at Tanjore (Lat. 11°) we have to add as correction, according to Table XIII [Lat. 11° (Tanjore)—208th day of Hindu Solar Year, on 6th Nov., when the Solar Year commences on 13 April] + 994 seconds of time = 41 palas.
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44 ghaṭikas 54 palas + 41 palas = 45 ghaṭikas 35 palas, after sunrise at Tanjore on 6th November, A.D. 1910.
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This is the absolute ending moment of "Mūla" Nakshatra in Lunar Kārttika, A.D. 1910 (Kaliyuga 5011), according to the Surya Siddhānta. According to Mr. Srauti's Panchāngam, which is based on the Greenwich Nautical Almanac, the absolute ending moment is 52 ghaṭikas 24 palas and according to the Kanjanur "Panchāngam (No. 28)" it is 47 ghaṭikas 16 palas.
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43. Suppose that in the same month we required to know the ending moment of No. 13 "Hasta" Nakshatra, instead of No. 19 "Mūla", we would have to take the "Interval" in Table XI for No. 13 and deduct therefrom the equivalent of 25·9184, i.e., 1·9383, which is the same for all months and all nakshatras throughout the Solar Year 1910 A.D. Against No. 13 under the 7th New Moon in Table XI there are two "Intervals", i.e., 0·0638 and 27·3854. We take the second interval as we cannot deduct 1·9383 from the first interval.
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| Nakshatra Interval. | Days. | ('s Anomaly. |
| 27·3854 | 216·3049 | 0·535 |
| -1·9383 (Annual Nak. Corrn.) | | 11·856 |
| 25·4471 | | |
| | + 25·4471 | + 25·447 |
| | 241·7520 | 37·838 |
| | | - 27·555 (1 an. month.) |
| | | 10·283 |
| Nakshatra equation for ('s anom. of 10·283 days | -·2915 | |
| (Tab. IX-J.) | | |
| | 241·4605 days | from 1st April, i.e., |
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(by Tables VIII and XIX) 27 ghaṭikas 38 palas after mean sunrise on 27th November, A.D. 1910.
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44. Lastly, if we want the ending moment of No. 15 " Svāti " Nakshatra in the same month, we find two " intervals " for No. 15 in Table XI, from each of which 1·9383 can be deducted. In other words, there will be two " Svāti's " in Lunar Kārttika 1910; one about 2·08 minus 1·94 or at 14 of a day after new moon and the other at 29·41 minus 1·94 or 27·47 days after new moon. The equation for the mean anomaly of the first Svāti will be that for an anomaly of 0·53 + 11·86 + 14 = 12·53 days : in this case the equation is - 118. The absolute ending moment of the first Svāti will be 305 + 14 - 118 = 327 or 19¼ ghaṭikas after mean sunrise on the new moon day, i.e., the 216th from 1st April, or 2nd November, A.D. 1910.
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The equation for the C's mean anomaly at the ending moment of the second Svāti will be that for (0·53 + 11·86 + 27·47 - 27·55) = 12·31 days ; that is, by Table IX-j, the equation will be - 138.
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The absolute ending moment of the second Svāti will then be 216·3049 27·47 - 138 = + 27·332 . . . . . 243·6369 days from April 1, i.e., (by Tables VIII and XIX) 38¼ ghaṭikas on 29th November, A.D. 1910.
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This is midway between Mr. Srauti's time (36¼ ghaṭikas) and the " Kanjanur " time (41 ghaṭikas) for the nakshatra in question. N.B.—We have not corrected our result for local time.
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45. Besides the system of the division of the moon's path among the stars into 27 equal nakshatra spaces, there are two others, called Garga's system and Brahma's system, by which the sidereal month of 27·32166 days is divided into 27 convenient but unequal stages. Our Table III gives the collective duration of the nakshatras according to the unequal systems, and the ending moment of each nakshatra according to either of these systems can be found by adding the corresponding collective duration to the ending moment of the last Nakshatra Revatī, which should be first determined. We have also given in Table III the names of the deities presiding over the several nakshatras.
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46. It is sometimes found that an extra Nakshatra Abhijit is interpolated between Nos. 21 and 22. Its duration is shown in Table III in the column dealing with " Brahma's System ".