sidereal right ascensions, 7

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The rigorous precession in right ascension and declination can be used to

apply a precession-correction whenever the positions are derivative from

the radix, i.e., when " precession-corrected tropical " is applicable. Since

precession from this perspective accumulates from the time of the radix

only, instead of from A.D. 221, the resulting displacement of the right

ascensions and declinations is relatively small.

 

Riyal --for example-- has always performed this precession correction by

default, unless the " precession-corrected " global option is de-activated.

And because I had assumed that sidereal astrologers always used sidereal

coordinates --I was wrong--, when Riyal works in " absolute sidereal mode "

(e.g., with positions in the Fagan/Bradley sidereal zodiac), the

precession-correction from the time of the radix cannot be deactivated. To

de-activate it, one must put the program back in tropical mode.

 

Later on, I learned --to my surprise-- that normally sidereal astrologers,

including Fagan, did not apply precession-correction to the right

ascensions and declinations, i.e., did not work sidereally but tropically,

or worked sidereally in some cases, tropically in others. Until someone

explains to me the logic of this, this makes little sense astronomically

and for this reason Riyal in sidereal mode forces the precession correction

from the time of the radix (e.g., bija rates of progression,

precession-corrected right ascensions and declinations, etc.).

 

When the same precession correction is applied rigorously to the longitudes

and latitudes, the nutation in longitude must be removed. When one

considers the ecliptic of t0 (=birth or whatever other time one chooses) as

fixed, then by definition it is removed from the Earth and becomes

" sidereal " , therefore, the transits to this fixed ecliptic are free of the

polar wobble that constitutes nutation. (I must thank Dieter Koch,

co-author of the Swiss Ephemeris, who in a recent e-mail exchange made this

clear to me.)

 

Since the conventional, approximate " ayanamsa method " of precession in

longitude does not take this into account, it contains *at all times* an

error in the positions varying from 0 to about 18 arcseconds. This error is

periodical, and independent of the other, much smaller but cumulative

(secular) error in the longitudes which results from ignoring the effects

of precession in the latitudes.

 

When one works in a sidereal reference, all transiting positions are

measured with respect to it and are therefore free of nutation; but there

is a difference of opinion with respect to how one takes the original natal

positions. If they are considered sidereal positions to start with, the

precession should be removed from the natal positions; this is the approach

of the Swiss Ephemeris. But it seems to me that the natal positions are

fixed-tropical, not fixed-sidereal. It is their tropical positions, the

tropical zodiac at the time of birth, what is being fixed in inertial space

or the space of the fixed stars, and therefore nutation should not be

removed from the natal positions.

 

A precession-corrected transit can be defined as the time when a transiting

planets crosses exactly the same point *in the natal ecliptic* at which a

natal planet was when you were born. The ecliptic at the time of the

transit has moved with respect to the ecliptic at the time of birth (at a

rate of approximately 47 " per century). The ecliptic at the time of birth

is considered fixed in the space of the fixed stars, but the natal planets

are referred to this ecliptic plane and not the stars, and therefore should

include the effects of nutation.

 

In other words, the original natal positions are not " sidereal " to start

with, but tropical. Then, this tropical ecliptic is frozen in inertial

space, and the transiting planets are measured with respect to this fixed

ecliptic of birth. Transits are measured not with respect to the sky of the

fixed stars, but to the ecliptic of birth. Obviously, if we are working

sidereally all along from the start, then of course the natal positions

should not include the nutation.

 

If you have been able to follow this discussion since the first post

(sidereal right ascensions 1), you will realize that this takes us to the

original concept of a starting point in time. In a precession-corrected

tropical scheme, the time of birth or of the radix is unquestionably the

starting point, but, is there such a starting point *in time* in the

sidereal zodiac? Should there be one? There is no question that one should

remove the nutation from the Fagan/Bradley (or any other) sidereal zodiac,

but should we rigorously correct for precession the positions to A.D. 221?

 

It seems that I already answered this in my reply to Gary, where I wrote:

 

" In normal practice the longitudes are being calculated back to A.D. 221

all the time because one is using an amount of accumulated precession (the

ayanamsa) that is valid only for a starting point in A.D. 221. One is

normally not aware of this fact because the correction is seen as a simple

displacement of position along the circumference of the zodiac (a spatial

consideration), without realizing that precession is both in space and

time. Precession has no meaning if it is seen only in terms of space. "

 

However, this is only as far as I can see at the moment. I remain open on

this.

 

Juan