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Nirayana – Method And Classification Of Nakshatras

Nirayana in Hindu astrology is the method and classification of nakshatras or birth stars. All stars near the ecliptic are divided into twelve groups of nearly equal sizes. They are the twelve zodiac signs, i.e., rashis. The same belt also divided into 27 parts, constituting the 27 Indian constellations known as nakshatras. In order to start counting these rashis and nakshatras, there must be some specified reference point. There are two methods to fix such a starting  point, and the assignments of numbers (and names) to these rashis/nakshatras follow two different systems, known as Nirayana system and sayana system.

In Nirayana system, the starting point is fixed in space. It is an important star knownas “Zeta Pisuim” in Revati Nakshatra. It is customary to proceed towards the east from this star along the ecliptic, and mark a point after every 13 degrees 20 minutes of arc. Thus there would be 27 parts of the ecliptic belt, forming 27 Nirayana nakshatras. Similarly, by starting from the same point and moving eastward along the ecliptic, (if the groups are formed of different arcs of the ecliptic each subtending an angle of 30 degrees at the center of the ecliptic), a total of 12 groups are formed. The stars and various other heavenly objects in these groups form twelve fixed rashis known as Nirayana rashis.

In Sayana system, the starting point to count rashis and nakshatras in the Vernal Equinox. The procedure of marking rashis and nakshatras is, however, the same as that followed in Nirayana system. The Vernal Equinox is not fixed point in space. In fact, it shifts slowly in the opposite (western) direction along the ecliptic and hence the rashis and nakshatras, demarcated with respect to this unsteady starting point, do not always show the same star combinations. They are known as Sayana (unsteady) rashis and nakshatras. Weather seasons depend on the equinoxes, and hence they can be correctly stated in terms of Sayana nakshatras. Nirayana nakshatras cannot be used to state the occurrences of the seasons correctly.

Western services use the Sayana system. Indian almanacs follow the Nirayana system.