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Methodology of Use of Nakshetra
The apparent shift of the Sun on the ecliptic is accompanied by an obvous change of season. These changes are commemorated on the local lunar and religious festival calendars. While the ecliptic migrates by 47 degrees, Orion shifts very little. This then ensures exclusive time zones when apparent (naked-eye observation) alignment of the ecliptic and Orion can happen. In fact, approximately 100 years from now, such an alignment is to happen on latitude +20 degrees (Bhubaneswar / Ekamra).
The ecliptic establishes a prominent east-west line, marked by the trajectory of the Sun at day, and by planets and the stars Regulus (alpha Leo) and Taurus (alpha tauri) at night (a fact relevant to day and night sailing). No such north-south line is available (in fact, the stars on the north and south horizons vanish and reappear seasonally with the shift in the ecliptic.
In the above diagram, we find no star in either the North or South that might mark a zone of the nine-pointed stellar Nakshetra.
On the other hnd, the four corners (NE, NW, SW, and SE) are prominently marked by the following stars:
- a Urs majoris / Dhube / Kratu (declination etc)
- a Cass /Cassiopeia/ kasyapa
- a Hyd /Archarner / Nadimukha
- a and b Crux / S Crux / Trisanku
There are also stars marking out the zones (khetras) between these four stars.
This is of extraordinary value to a mariner on the high seas.
Any one pair of this four cornered guide, or embryonic compass, is located over the globe between latitude +60 degrees and lattitude -60 degrees. Each star pair was thus separated from its opposite pair by around 10 to 12 hour of arc (and there is a complimentarily of 60 and 70 degrees in angle as well). In either case the navigator is able to align any one corner-star of the Orion Trapezium with another, far beyond, thus marking a zone/khetra. As he voyages across the equator, from north to south, the northern pair falls toward the horizon while the southern pair rises in declination. The opposite is true for a voyage from south to north.
Assuming the sailor's point of demarcation and destination were aligned with (and identified with) prominent stars / khetras; he could
home-in on that center of Orion that is approximated with the Indian subcontinent (more precisely Ekamra Or the mouth of river Prachi) from as far as latitude -60 and latitude +60. In other words, he could sail out to peripheral zones of the Nakshetra with the onset of winter in the northern hemisphere, and return with the summer solstices. Conversely, he could march out on land with the onset of spring (coastal belt) and return with northern winter (all dictated by fair weather).
Using a model of the star-earth correlation carried aboard-ship, the seasoned and well-groomed mariner could crisscross the seas, stick to track, revert back to track in case of inclement weather, and maintain schedules, simply by fixing the point of start in reference to destination and adopt a simple, linear interpolating technique (as one discussed above). There may have indeed been a subsequent step, culminating in its celebration in stone art as the crowning piece of achievement.
Nakshetra is nothing but a theoretical, celestial intra-star that may have acted as a guide for the ancient unknown mariner. Later, it may have inspired a copy by the more able or the then learned men; of course backed by heritage and patronage - a conjecture supported by local archaeology.
Each Star, marked a particular Khetra, also marked a destination or geographical landmark. Thus the sailor had more than one star by which to
steer his ship - he had a stellar instrument. He called this instrument the Yantra11
and is said to have taken "great care not to allow
anyone to touch it...." (milinda prasna).