The Suppressed Month
What is a Kshayamasa or suppressed month? At times, a lunar month can completely cover a shorter solar month. Then the Sun's stay in a Rasi will be less than the duration of a lunar month. This will result in two Samkramanas or solar ingress occuring in a particular lunar month. In such a contingency there will be no New moon in that particular solar month. Therefore, there will be no lunar month to be named after that solar month. Obviously this will create a gap in the sequence of names of the lunar months, missing out one name. This dropped out month is callled Kshayamasa or decayed month.
In such years when a lapsed month occur (this happens less frequently) there will be two inter-calary months or Adhikamasas, one before the Kshayamasa and the other after that, within a span of three months on either side. The inter-calary month occuring prior to the Kshayamasa is called Samsarpa and this is generally exempted from the injunctions of performance of religious festivals in that month, as attributable to normal Adhikamasa. The latter inter-calary month is called Amhaspati and this second Adhikamasa will be the correct Adhikamasa, as it occurs after 30 months of the previous Adhikamasa.
Though the average length of a lunar month is 29 days, 12 hours, 44 minutes, it actually varies from 29 days, 5 hours, 54 minutes to 29 days, 19 hours, 36 minutes depending on the position of the New moon of the lunar perigee (Surya Siddhanta gives the limits as 29 days, 6 hours, 18 months to 29 days, 19 hours, 6 months). as the months of Vrischika, Dhanus and Makara have their lengths between these two limits, only the lunar months of Margasira, pushya and Magha can become Kshaya more often than the other two and Magha, the least.
To summarise, a Malamasa or Adhikamasa occurs when there are two New Moons in a solar month creating a situation of absence of any solar ingress or Samkramana in that lunar month. For an Adhikamasa to occur, a solar ingress must take place just before a New Moon and the next ingress must be just after the next New Moon. Or in other words, a lunar month with no Samkrantis of the Sun occuring in it is called a suppressed month, Kshayamasa or Amhaspati.
A decayed month or Kshayamasa occurs when there is no New Moon in any solar month creating a situation of two solar ingresses or Samkramanas happening in that lunar month. For a Kshayamasa to happen the solar ingress must happen just after a New moon and the following solar ingress must take place before the ending of the next New Moon. In other words a lunar month will two Samlrantis of the Sun occuring in it is called a suppressed month, Kshayamasa or Amhaspati.
Much variance in computational factors is found in the different ancient astronomical treatises as regards the length of the solar year and the like. Different Siddhantas are followed in different regions of different people. The opinions expressed in various Sastriac texts are also in variance with regard to the observances of religious festivals. Therefore there is difference of opinion amongst scholars in determining some of these Adhika and Kshaya months. Only some of the basic principles have been discussed here to give the reader a general but clear idea about the subject, without going into the intricacies.
