Certainly first I offer my respect to PVR Narasimha Rao Jī. However, I disagree with his paper on ayanāṁśa from the outset. Maybe fate will have it that he will correspond to discuss and clarify these points.
He says he has figured out “an ayanamsa based on Surya Siddhanta” and then goes on to say that the astrological zodiac cannot be tropical. However Surya Siddhanta clearly defines the zodiac is tropical (i.e. no ayanamsa) so, how shall we have faith that he is really basing his ideas on Surya Siddhanta? Viz. Chapter 14.7-10:
“It is well-known that the circle of signs is split by two diameters. One is the line from equinox to equinox. The other is the line from solstice to solstice. Between each solstice and equinox are two other markers. Each solstice /equinox and the two following markers represent the three strides of Vishnu.
The Sun has entered Capricorn when it begins moving north for six months. It has entered Cancer when it begins moving south for six months. Seasons last for two signs each, beginning from Capricorn with the frozen season. The twelve signs named Aries, etc. are the months which altogether comprise the year.”
Surya Siddhanta gives no other definition of the zodiac.
In the “Tropical vs. Sidereal Zodiacs” section of his paper, he says:
“Zodiacal signs are supposed to be aligned to nakshatras, which correspond to constellations of stars in the sky. For example, the sign of Aries should contain Aswini nakshatra, Bharani nakshatra and a part of Krittika nakshatra. If we use the tropical zodiac, signs will slowly shift with time and point to different nakshatras in different eras. This is totally inconsistent with the teachings of rishis.”
Can he quote one single Rishi who says that nakshatras and the zodiac are irrevocably and permanently related, as he claims they say? I would be extremely surprised if he could, since I have also scoured the statements of the Rishis and have found no such words.
When astrological texts correlate the nakshatras to zodiac signs, they do so relative to the conditions current at the time of writing. Thus no classical author minded that Rg and Atharva Veda list Krittika as the first nakshatra, they went ahead and listed Asvini first – because Krittika was first when Rg was written and Asvini had become the first (ie. aligned with the vernal equinox) in classical times. Shortly after the classical period, people seem to have developed a different idea – that the relationship between nakshatras (stars) and signs must never change. This is not a statement of a rishi, it is a modern misunderstanding. Perhaps modern people with this misunderstanding consider themselves, or are considered by others as “Rishi” but I don’t agree.