Page:Sewell Dikshit The Indian Calendar (1896) proc.djvu/41

Vedâṅga-jyotisha; and from the time when the zodiacal-sign-names, "Mesha" and the rest, came into use till the present day, the general rule has been that that amânta lunar month in which the Mesha saṅkrânti occurs, is called Chaitra, and the rest in succession.

45. Adhika and kshaya mâsas. It will be seen from Art. 24 that the mean length of a solar month is greater by about nine-tenths of a day than that of a lunar month, and that the true length of a solar month, according to the Sûrya-Siddhânta, varies from 29 d. 7 h. 38 m. to 31 d. 15 h. 28 m. Now the moon's synodic motion, viz., her motion relative to the sun, is also irregular, and consequently all the lunar months vary in length. The variation is approximately from 29 d. 7 h. 20 m. to 29 d. 19 h. 30 m., and thus it is clear that in a lunar month there will often be no solar saṅkrânti, and occasionally, though rarely, two. This will be best understood by the following table and explanation. (See p. 26.)

We will suppose (see the left side of the diagram, cols. 1, 2.) that the sun entered the sign Mesha,—that is, that the Mesha saṅkrânti took place, and therefore the solar month Mesha commenced,—shortly before the end of an amânta lunar month, which was accordingly named "Chaitra" in conformity with the above rule (Art. 14, or 44); that the length of the solar month Mesha was greater than that of the following lunar month; and that the sun therefore stood in the same sign during the whole of that lunar month, entering the sign Vṛishabha shortly after the beginning of the third lunar month, which was consequently named Vaiśâkha because the Vṛishabha saṅkrânti took place, and the solar month Vṛishabha commenced, in it,—the Vṛishabha saṅkrânti being the one next following the Mesha saṅkrânti. Ordinarily there is one saṅkrânti in each lunar month, but in the present instance there was no saṅkrântiwhatever in the second lunar month lying between Chaitra and Vaiśâkha.

The lunar month in which there is no saṅkrânti is called an adhika (added or intercalated) month; while the month which is not adhika, but is a natural month because a saṅkrânti actually occurred in it, is called nija, i.e., true or regular month.^[1] We thus have an added month between natural Chaitra and natural Vaiśâkha.