SIGNIFICANCE OF THE NIRAYANA METHOD

Zodiacs are nothing but the constellations along the ecliptic on the celestial sphere. There are 12 constellations along the ecliptic, each in a 30°segment, as accepted by the IAU. We measure the celestial longitude of these segments from a reference point known as the vernal equinoctial point, as per modern astronomy.

In Western astronomy, they also consider the equinoctial points to define the constellation along the ecliptic. But if we observe these points with reference to the background fixed stars by an observer sitting on Earth, these points seem to move approximately 1° every 72 years; this phenomenon is known as the precession of the equinox or solstice. So, if we calculate celestial longitude and latitude, or right ascension and declination, i.e., the coordinates of the constellation or fixed star with reference to the vernal equinox point, which is not fixed, then their coordinates will also change on a regular interval; we cannot locate them in the same place on the celestial sphere. Likewise, the position of the zodiac or asterism will also change with respect to the vernal equinoctial point.

In Western astronomy, the first zodiac, Aries, starts with the vernal equinoctial point. Since the point itself is moveable, the zodiac will also move. This system is known as the Sayana System or tropical system .

In the Hindu astronomy method, the first zodiac, Aries, starts with a fixed point instead of a vernal equinoctial point. They take a fixed star as a reference point to calculate the coordinates of any stars or constellations. Then they set up a fixed zodiac system along the ecliptic. Making these a reference system, they trace all these constellations and stars and equinoctial points. So, the position of the zodiac or asterism will not change. Instead, they allow the movement of the equinoctial points with reference to the Zodiac System. This system is known as the Nirayana method or the Sideral method.

We can consider the sideral method to calculate how much the equinox and solstice points shift from their starting points and trace the precession of the equinox over a very long period of time. Once we trace the cardinal points with respect to their starting point, it is easy to correct the longitude and latitude of celestial bodies on the celestial sphere, as well as resetting the calendar to avoid being out of sync with seasons. Similarly, western calendars only follow tropical calculations, so their calendar is also out of sync with equinox and solstice days and will be out of sync with the seasons in the future. So, when making a calendar, we have to consider both the model and the calculations.

A calendar is primarily used for keeping track of time, navigation, and seasonal information for farming. Equinoxes and solstices are connected to seasons from an astronomical perspective. The equinox and solstice dates of the Gregorian calendar were set in relation to the calendar. The vernal equinox point was fixed on March 21 by deducting certain days, roughly 11 days, from the Julian calendar because the equinoxes' precession causes these points to move with respect to the calendar . Thus, for a brief period of time, the Gregorian calendar was in line with the seasons; nevertheless, over time, it too drifted away from them. The calendar was created using tropical year lengths, making it a tropical calendar. The Hindu calendar (Pañcāńga) is a sideral calendar since it was created using the sideral year length.

In spite of the Indian National Calendar (a Tropical Calendar), which was proposed by the Calendar Reform Committee under the chairmanship of Prof. Meghanad Shah, numerous people in India still use lunisolar calendars, in which the length of a year is determined by the movement of the sun and the sidereal moon cycle determines the months. Hindu calendars (Pañcāńga) vary slightly from one another in terms of computations, depending on the locale. This is so that Pañcāńga, which is not exclusively astronomical, may take into account local geography . Based on the geocentric paradigm, all of these calendars use observations of the planets and stars made from Earth to make computations. The date of New Year's is also flexible. They do not determine the duration of a year using the four equinoctial points, as is the case with the solar tropical calendar. In this concept, they calculated the length of a year using 0 Aries (a fixed star in the Aries constellation) as their reference point along the ecliptic. A reliable calendar that could reliably forecast the monsoons was necessary for agricultural success. A reliable calendar is required for the accurate measurement of seasons because agriculture accounts for a substantial portion of India's economy. Thus, it is necessary to use both tropical and sideral methods of calculation.

The lunisolar calendar that we use in India seems to be out of sync with the seasons because the Nirayana Winter Solstice (Makar Sankranti or Uttarāyana) given by the lunisolar calendar falls approximately 23 or 24 days after the Tropical or Sāyana Winter Solstice (which is actually observed by a person on Earth). Similarly, with the Summer Solstice, Vernal Equinox, and Autuman Equinox, which are the basis for synchronisation of seasons with the calendar, But the calendar is not actually out of sync with the seasons; our ancient astronomer used a different method for this synchronization. The correct tropical values are obtained by adding Ayanāṃśa to the nirayana calculation in order to bring Pañcāńga into harmony with the seasons. So, tracing of this Ayanāṃśa value is the most important factor for the lunisolar calendar to remain sync with the seasons and make the timekeeping method of the calendar not vary for a longer time period . Ayanāṃśa is the arc length along the ecliptic measured from the zero point to the vernal equinox point in degrees, arc minutes, and arc seconds. So, if we use the Nirayana method for making a calendar, we can use this calendar for a very long period of time.