सिद्धान्तदर्पण (महामहोपाध्याय सामन्त चन्द्रशेखर सिंह - नग्न-नेत्र खगोल वेध एवं गणित महाकोश)

Introduction xli
But before any reformation is attempted, an
exact determination of the amount of precession
becomes a question of paramount importance. The
reader is a awre that in the Hindu system, the
longitudes of celestial bodies are measured from a
fixed point - say a star - in the ecliptic, instead of
from the movable vernal equinox as is the practice
in Europe. The question has therefore the same
bearing upon our calculations, as the position of the
so called First Point of Aries upon those of the
Nautical almanac.
Unfortunately, all attempts to solve the*
question have been practically fruitless. The reader
will hence understand the chaos into which our
almanacs have sunk. The gravity of the situation,
and the difficulty of escaping from it, demand a
fuller discussion than our space would permit. But
then this alone can give us an opportunity of
ascertaining Chandrasekhara's success in this
direction.
Promising, then, that we measure longitudes of
planets from a fixed point in the ecliptic, the
question resolves itself into a determination of the
point. In other words, what is that point, or what
is its longitude from the vernal equinoctical point ?
Whatever and wherever that point may be, it is the
starting point of our zodiac, and its longitude is
known as ayanamsa, which literally means amount
of solstices. For, we do not speak of the precession
of the equinoxes as often as we do of the precession
of the solstices. Hence, the ayana-chalanam of
Sanskrit astronomy is equivalent to the precession
of the equinoxes. To avoid ambiguity we shall use
the term ayanamsa rather than the amount of
precession.