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Unamasa in Hindu Calendars

Unamasa, also known as Kshayamasa, is a salient feature of Hindu lunar calendars. The Indian almanac considers periodic motions of both sun and the moon for determining the units of time. In order to correlate the two systems of time determination the practice of adhikmasa and kshayamasa is introduced.

The event of the sun’s entry from one zodiac sign to another zodiac sign is known as Sankranti. Normally, only one Sankranti takes place in one lunar month. However, due to very fast speed of orbital motion (apparent) of the sun, sometimes two such transits of the sun occur in a single lunar month. That month is known as kshayamasa.

As a result of such double transits of the sun in one lunar month, a month prior to it and a month after it are characterized by no solar transits at all. They are therefore the Adhikmasa. Therefore, the lunar month preceding the kshaya masa is known as samasarpa, while the one following the kshyamasa is called anhaspati. The kshyamasa is named as malamasa.

As the sun’s orbital speed is very high in the months of Kartik, Margashirsha and Pausha, any of them can become kshayamasa. It is found that kshayamasa occurs every 141 years. Then after 19 years from does another kshaya masa take place. In the year 1681 CE there was a kshayamasa, and hence it occurred again in 1822 CE and then in 1841 CE. The last kshayamasa occurred in 1983 CE. We find references of kshayamasa in the great epic, the Mahabharata.