SIDEREAL RIGHT ASCENSIONS
by Juan Antonio Revilla
Sidereal astrologers work by necessity with sidereal coordinates... or
so one would think. In practice, the truth is that while sidereal
longitudes are used, when it comes to the right ascensions and
declinations (e.g. in the calculation of parans), and the latitudes,
almost always tropical positions are used exclusively. This seems to be
a contradiction, and it brings to the surface some practical problems
regarding sidereal astrological techniques that I would like to discuss
in some detail.
Definition of the ayanamsa
The ayanamsa can be defined as the amount of precession (in longitude)
accumulated from one date (the epoch) to another. Since precession is a
function of time, the ayanamsa definition requires an epoch or starting
point in time. This "zero point" is traditionally described as the time
when the spring equinox coincided with the pre-defined origin of
coordinates or fiducial, which may be a fixed star, the time of a
peculiar astronomical alignment, or an empirically or statistically
derived more or less "fixed" point in space, a point that is not
subject to precession.
The fixed point belongs to the sidereal or quasi-inertial reference
frame, against which moves or rotates with varying velocity the
tropical reference frame, subject to precession.
We can also define an ayanamsa as simply an angle or an arc of the
circumference between the tropical zero point and an arbitrary sidereal
zero point of longitude established by convention. This arc of
celestial longitude, as in the traditional definition, is dynamic, and
changes as the moving tropical zero point is dragged by the Earth's
precessional motion away from the sidereal zero point.
The difference between the two definitions lies in the absence in the
second definition of a historical coincidence in the past between the
tropical and the sidereal zero points, or in other words, the absence
of the concept of an "original", historical sidereal zodiac, defined by
its zero point coinciding with the spring equinox of a certain moment
in the historical past.
The sidereal zero point can be defined anyway one wishes. The only
requisite is that its starting point in time be clearly defined. There
is no need whatsoever of a historical tradition about the beginning of
the sidereal zodiac coinciding with the spring equinox of some
historical era. Its zero point does not have to be defined in terms of
a historical spring equinox. The only thing needed is that it is fixed
to a pre-defined zero point in time.
In astrological, mathematical terms, whether the sidereal zero point
corresponds to some historical Spring Equinox is irrelevant.
The first definition is behind the several "sidereal" astrologies based
on an assumed historical sidereal zodiac the zero point of which is
"truer" than all the others. The second definition is behind the usual
practice of erecting precession-corrected solar returns.
Let me make some general statements to describe what --normally-- sidereal astrologers do astronomically speaking:
1-) represent the zodiacal positions of planets using a fiducial (the
particular sidereal zodiac) which is approximately free of precession
in longitude. In practical terms, the tropical positions are used as a
source, and a simplified formula of precession in longitude is applied
to them that ignores the effects on the longitude of the motion of the
moving ecliptic over the fixed ecliptic.
2-) ignore the precessional displacements in latitude, right ascension,
and declination. In practical terms, use the sidereal zodiacal
longitudes obtained from the approximate method above, but keep working
with the tropical latitude. If needed, strictly tropical --not
sidereal-- right ascensions and declinations are often used.
3-) use tropical, not sidereal, time-units with sidereal positions, and
viceversa, use sidereal time units but tropical positions. In practical
terms, when the "bija" corrections in progressions are ignored,
sidereal astrologers use tropical time units with sidereal positions,
or, as in the parans of the PSSR, use sidereal time units with tropical
Very often astrologers believe that they are working in a sidereal
reference frame simply because positions are being represented in the
(or a) sidereal zodiac, whereas the zodiac in which one chooses to
represent the positions is irrelevant.
When a spatial relationship (the representation of position in the
tropical or in a sidereal zodiac) is considered in isolation of the
corresponding time relationship (using tropical or sidereal time
units), we see the practice among some siderealists of calculating
secondary and tertiary progressions without the "bija" correction,
which is equivalent to working with tropical measurements while
representing the results in the sidereal zodiac.
This is not a sidereal but a tropical calculation, and in order to be
consistent one would need also to calculate the time of transits
Because in the calculation of transits no time-transformations are
necessary, i.e., the relationship between time units is 1:1, only the
spatial relationships are considered. However, one becomes aware of the
time dimension in transits when comparing the difference in time
between a tropical and a sidereal transit. This difference is a good
illustration of how space and time are always together and inseparable.
Another illustration of an inconsistent practice is when tropical
astrologers use precession-corrected solar returns (the concept of
"return" is a seemingly time-based concept), but keep calculating
transits in a tropical-only reference frame (transits having the
semblance of merely spatial relationships).
I suggest that these inconsistencies happen mainly for 2 reasons.
First is the habit of astrologers of conceiving things spatially --in
this case, as a simple displacement of position in longitude (the
Ayanamsa) representing the traditional, simplified application of
precession-- instead of dynamically, i.e., as a change in the space
*and* time system of reference required by a rigorous application of
the dynamics of precession. This idea of time is the essence of
precession, and not the seemingly spatial-only relationships or
"displacements" with which one associates shifting from a sidereal to a
tropical (or viceversa) reference frame.
There is tendency to pay attention only to the spatial relationships or
measurements, forgetting that space and time are always related and
inseparable. The proof of this is than in sidereal practice, it is
often assumed that the only thing needed is a "horizontal" displacement
of longitude with respect to the tropical position (the spatial
emphasis), leaving aside the displacements in a-) latitude, b-) right
ascension, and c-) declination.
Second, the word "sidereal" is not understood in its astronomical
sense, i.e., as a reference frame "fixed" in time and space, but in its
astrological sense, i.e., representing zodiacal longitudes in a
traditional, historical, "sidereal zodiac" based solely (and
artificially) on an approximate formula of precession in longitude.
These inconsistencies would disappear completely if:
- the word "sidereal" were associated with the reference frame and not with a particular traditional sidereal zodiac
- sidereal time units were used with sidereal positions, tropical time units with tropical positions
- rigorous precessional corrections to all coordinates were used instead of the artificially simplified ones
- the sidereal zero point were understood in space as well as in time.
Before continuing, it may be useful to offer an astronomical definition
of the word "sidereal". The conventional definition is "measured with
reference to (or in the background of) the stars". My Anchor Dictionary
of Astronomy edited by Valerie Illingworth (New York, 1980) provides
this definition on page 406:
"sidereal. Related to or measured or determined with reference to the stars".
This definition is tautological, because it does not explain what "with
reference to the stars" means. A better definition is given further
below (emphasis mine):
"sidereal month. The time taken by the moon to complete one revolution
around the Earth, measured with respect to a background star or stellar
group CONSIDERED FIXED IN POSITION".
"sidereal year. The time taken by the Earth to complete one revolution
around the Sun with reference to a background star or stellar group,
which is REGARDED AS FIXED IN POSITION".
In other words, "sidereal" means a fixed stellar reference frame. A
reference frame fixed in space and devoid of motion or rotation is
called "inertial". Because stars have proper motion, in practice,
astronomers use a "quasi-inertial" frame based on a "fundamental
catalog" (such as the FK5), consisting of reference stars with very
well-known proper motions, and in the last years, for more accuracy a
standard set of very distant radio sources with negligible proper
motion instead of fundamental stars has been used.
Astronomers invariably use the stellar or sidereal reference frame to
calculate ephemerides of solar system objects. This is necessary in
order to model as accurately as possible their motion (hence the term
"dynamical reference frame"). Extreme efforts are taken in order to
arrive at the ideal inertial space, presently defined arbitrarily
around the mean equinox and ecliptic of January 1, 2000 (J2000).
Once planetary positions have been calculated for J2000, precession,
nutation, aberration, etc. are applied in order to establish the "of
date" apparent geocentric coordinates which are found in astrological
ephemerides. But the reduction from J2000 to apparent position is made
rigorously, applying precession also to the latitudes and accounting
for the effect of the latitude on the precession in longitude, a factor
that is ignored by sidereal astrologers, who use the tropical positions
as source to convert back to their "quasi-sidereal" reference frame and
results in inaccurate, approximate positions.
The use of J2000 to represent positions is equivalent to using the mean
equinox and ecliptic of J2000 instead of A.D. 221 (in the case of the
Fagan/Bradley zodiac) or the time of birth as zero point. The
difference is that it is done rigorously. If one were to take
rigorously A.D. 221 as the zero point of coordinates, the long
time-span from then to the present would result in displaced
coordinates when compared with the standard astrological procedure. In
my next post I will illustrate these differences with an example.
Normally, sidereal astrologers do not apply precession to the
coordinates of a radix. What they do is REPRESENT THE LONGITUDES IN THE
SIDEREAL ZODIAC, i.e., add the ayanamsa to the longitudes only, keeping
the representation of latitude, declination, and right ascension
In order to apply rigorous precession to the longitudes, latitudes,
right ascensions, and declinations, we need to know the epoch or zero
point of the coordinates. Having the position of the ayanamsa in the
tropical zodiac --the usual procedure-- is not enough. We need to know
when in time the ayanamsa was exactly zero.
Using the Bureau des Longitudes precession formulas, the resulting
epoch (the root of the polynomial used to calculate the Fagan/Bradley
Ayanamsa) is September 11, A.D. 221, julian day 1802031.7973. This date
is dependent on the numerical quantities of precession in the ecliptic
and may vary if one uses other quantities. The BdL formulas, for
example, may have an error of in 1.8" or 1.9" in A.D. 221, so this date
may be off by about 2 weeks.
data used for the example: J.F. Kenedy dies, November 22 1963 UT 18h30m00s.
Let's see the positions with the usual procedure:
longitude latitude rightasc. decl.
Moon = 17Cp00'36" -2,33' 20h57m46s 19s51
Sun = 5Sc30'10" 0,00' 15h50m10s 20s06
Mercury = 15Sc30'59" -1,36' 16h31m20s 23s30
Venus = 27Sc13'01" -0,55' 17h22m30s 24s05
Mars = 26Sc17'32" -0,49' 17h18m30s 23s55
Jupiter = 15Pi34'59" -1,30' 0h38m26s 2n30
Saturn = 23Cp05'00" -1,12' 21h20m35s 16s48
Uranus = 15Le34'57" 0,46' 10h46m36s 8n36
Neptune = 21Li41'31" 1,43' 14h55m52s 14s58
Pluto = 19Le50'09" 13,40' 11h23m20s 18n50
The rigorous application of precession gives:
Moon = 16Cp59'43" -2,22' 19h15m09s 24s56
Sun = 5Sc29'41" 0,12' 14h12m53s 13s17
Mercury = 15Sc30'37" -1,23' 14h50m16s 17s58
Venus = 27Sc12'34" -0,42' 15h38m50s 20s24
Mars = 26Sc17'05" -0,35' 15h35m06s 20s05
Jupiter = 15Pi34'09" -1,33' 23h09m23s 7s10
Saturn = 23Cp04'18" -1,03' 19h40m32s 22s43
Uranus = 15Le34'18" 0,41' 9h13m11s 16n58
Neptune = 21Li40'44" 1,53' 13h22m53s 6s47
Pluto = 19Le46'26" 13,36' 9h48m19s 27n52
The first tabulation is a simple representation of longitudes after a
change of the zero point in the circumference. Although this is what is
usually called "sidereal", astronomically speaking it makes little
The second tabulation shows the positions in a truly sidereal reference
frame, defined by the ecliptic and equinox of the zero point in time of
the Fagan/Bradley ayanamsa. Note that, when the latitude is high as in
the case of Pluto, the difference in the longitude is more significant.
differences in longitude and latitude:
Moon = -0'53" + 11'
Sun = -0'29" + 12'
Mercury = -0'22" + 13'
Venus = -0'27" + 13'
Mars = -0'27" + 14'
Jupiter = -0'50" - 3'
Saturn = -0'42" + 9'
Uranus = -0'39" - 5'
Neptune = -0'47" + 10'
Pluto = -3'43" - 4'
Even though the time spanned from A.D. 221 to 1963 is considerable, the
differences in longitude are small, except in the case of Pluto,
although a difference of 4 arcminutes can still be considered small.
The differences in latitude are larger, but perhaps not very
significant because the latitude is little used anyway. The only common
use of latitude that I can think of is for converting to right
ascension and declination.
That the differences are small is encouraging. It means that one could
use a more rigorous precession method without having to deal with very
different results that would make them impractical.
The right ascensions and declinations are another matter, because in
sidereal practice they are strictly tropical, they are never precessed,
for reasons unknown to me:
differences in right ascension between tropical and A.D. 221:
Mercury = -0h41m04s
Venus = -0h43m40s
Jupiter = -1h29m03s
Saturn = -0h40m03s
Neptune = -1h32m59s
Pluto = -1h35m01s
differences in declination (in degrees and arcminutes):
Moon = +5,05'
Sun = -6,49'
Venus = -3,41'
Mars = -3,50'
Saturn = -5,55'
Uranus = +8,22'
Pluto = +9,02'
The differences in right ascension and declination, logically, are very
large, the coordinates totally different. Using them would require a
lot of experimentation in a previously unexplored field (as far as I
know), and personally, or intuitively, I am not tuned to this way of
handling the right ascensions.
However, using precession-corrected right ascensions and declinations
from the time of the radix will result in very small differences from
the strictly tropical coordinates, with the advantage that they would
be sidereal, instead of working sidereally sometimes, tropically
others, or using both sidereal and tropical within the same calculation
(as in the PSSR).
The practice of ignoring precession when dealing with the latitude, the
right ascension, and the declination of the planets evidences that
sidereal astrologers are using a definition of precession which is a
simplification of the astronomical complexities of precession in the
real world. This is not necessarily wrong as long as it is understood
that it does not correspond to the physical reality of precession.
In other words: sidereal astrologers often work with strictly tropical
--not sidereal-- coordinates. When tropical right ascensions and
declinations not corrected for precession are used, or when tropical
time units are the basis for the calculation of progressions (without
the "bija corrections") they are working in a tropical reference frame.
This happens because for most astrologers (tropical and sidereal alike)
the word "sidereal" means simply representing the zodiacal longitudes
in some historical or traditional zodiac (a merely spatial conception),
failing to see the time dimension, the fact that "sidereal" is not "in
such and such a zodiac" not subject to precessional displacement in
longitude, but a mathematically defined space and time reference frame.
examples of the paradigmatic emphasis on spatial relationships in
astrological thinking at the expense of more dynamical perspectives are
discussed in my essay "On the Seed Metaphor": http://www.expreso.co.cr/centaurs/essays/seed.html
The astronomical incongruence of the way astrologers deal with precession was discussed by Dieter Koch in the documentation to the Swiss Ephemeris. He wrote [see the section "In search of correct algorithms"]:
the whole ayanamsa is subtracted from a planetary position which is
referred to the ecliptic of the epoch t... Because the ecliptic is not
fixed, it cannot be correct just to subtract an ayanamsa from the
tropical position in order to get a sidereal position... This does not
make sense... The traditional method of computing sidereal positions is
geometrically not sound and can never achieve the same degree of
accuracy as tropical astrology is used to."
Dieter provides an example of what happens when the usual procedure of
adding the ayanamsa to a tropical position in order to (allegedly)
obtain its sidereal position is used over a long time span:
effect of this procedure, objects that do not move sidereally, e.g. the
Galactic Center, seem to move. If we compute its precise tropical
position for several dates and then subtract the Fagan/Bradley ayanamsa
for the same dates in order to get its sidereal position, these
positions will all be slightly different:
01.01.-5000 2 sag 07'57.7237 -4°41'34.7123 (without aberration)
01.01.-4000 2 sag 07'32.9817 -4°49' 4.8880
01.01.-3000 2 sag 07'14.2044 -4°56'47.7013
01.01.-2000 2 sag 07' 0.4590 -5° 4'39.5863
01.01.-1000 2 sag 06'50.7229 -5°12'36.9917
01.01.0 2 sag 06'44.2492 -5°20'36.4081
01.01.1000 2 sag 06'40.7813 -5°28'34.3906
01.01.2000 2 sag 06'40.5661 -5°36'27.5619
01.01.3000 2 sag 06'44.1743 -5°44'12.6886
01.01.4000 2 sag 06'52.1927 -5°51'46.6231
01.01.5000 2 sag 07' 4.8942 -5°59' 6.3665
effect can be much greater for bodies with greater ecliptical latitude.
"Exactly the same kind of thing happens to sidereal planetary
positions, if one calculates them in the traditional way. It is only
because planets move that we are not aware of it.
You can see here the precession in latitude, or more exactly, the
accumulated displacement between the ecliptic of the epoch (here 1950)
and the ecliptic of date, normally ignored in sidereal practice. You
can also see how the longitude is rotating or librating around its 1950
This example of a point which is known to be fixed or unmoving in
quasi-inertial space like the Galactic Center, shows to what extent the
usual sidereal practice is based not on a concept of "sidereal" as a
reference frame, but of "sidereal" as exclusively a representation of
zodiacal positions based on a conventional or traditional fiducial
point not subject to precession in longitude.
This is the traditional "sidereal astrology paradigm": represent the
zodiacal positions of planets using a fiducial which is free of
precession in longitude, but ignoring how precessional motion is in the
real world. Ignore the precessional displacements in latitude, right
ascension, and declination. But even the "sidereal" longitudes have
been calculated with a simplification of precessional motion in
longitude, so they are really "quasi-sidereal". The latitudes, the
right ascensions, the declinations, and often, the time units used by
sidereal astrologers, are often strictly tropical.
So, clearly, everything depends on how one defines the word "sidereal".
It is one thing to be a "sidereal astrologer" (including of course the
Indian version), and a different thing to work astrologically in a
sidereal reference frame. The two things are assumed to come together
in theory. They are separate in practice. If understood in the
astronomical sense, "Sidereal" astrology is not wholly sidereal, or it
is "sidereal" only in a limited, inaccurate and simplified way.
Since precessing the right ascensions and declinations would result in
very large differences with what has already been done, one would think
that it is in the use of PRECESSION-CORRECTED POSITIONS
--where the corrections are small-- where a real and practical, truly
accurate sidereal or "fixed", quasi-inertial reference frame can come
into place in Astrology.
In principle, "precession-corrected" (tropical) positions and "truly
sidereal" positions are exactly the same, the difference being only the
point in time that is chosen as fiducial:
1-) precession-corrected positions (usually) use the radix as fiducial
2-) sidereal positions use September 11, A.D. 221 as fiducial
NOTE: This date refers to the Fagan/Bradley sidereal zodiac, which I use as example in this exposition.
In other words: a "sidereal astrologer" uses the tropical zodiac of the
year 221 as fiducial, a "tropicalist" who works with
precession-corrected positions uses the time of the radix as fiducial.
Both are "precession-corrected" tropical positions, the only difference
is the amount of time or of accumulated precession which results from
the fiducial or starting point chosen. Both are sub-sets of a purely
sidereal (or quasi-sidereal) reference frame.
Astrological measurements can be either tropical or sidereal,
independent of whether one uses a tropical (or sidereal) zodiac
or not. That this is often not recognized is another example of how
much astrologers are controlled by a purely spatial abstraction at the
expense of the more realistic, dynamical model that includes both space
Confusion is created by the habit of associating the word "sidereal"
with a specific sidereal zodiac of some astrological tradition or
school. "Sidereal" is a system of reference to measure movement, and is
independent of any of the traditional zodiacs used by astrologers,
sidereal or tropical. The question of sidereal or tropical is not
simply a question of what traditional zodiac one uses, but a question
of how one wants to measure time.
If one subtracts the precession accumulated from the time of the radix
to the tropical positions of a specific date, one is effectively using
a sidereal zodiac with its zero point defined as the position of the
equinox at the date of the radix. The tropical position of 0 Aries when
a person is born is considered fixed in a quasi-inertial or "fixed"
reference frame, and precession is counted from that day on. A
precession-corrected tropical solar return is a strictly sidereal
construct based on a sidereal reference frame the starting point of
which is the radix.
Another way of saying it is that a "tropical" precession-corrected
return represents positions in a sidereal zodiac the starting point of
which is the vernal point of the radix, while a purely "sidereal"
return represents positions in a sidereal zodiac the starting point of
which is the vernal point of September 11, A.D. 221 (in the case of the
"Sidereal" is by convention a "fixed" reference frame, against which
the precessional motion is observed and measured. The astrological
concept of "a radix" is almost the same thing: something "fixed" in
time against which one charts everything that happens in time. From
this perspective, precession-corrected (=sidereal) solar returns and
transits appear to be the most logical way to proceed, since the birth
chart is conventionally considered "fixed" in time and space.
This is the principle behind the use of a sidereal reference frame.
What zodiac (tropical or sidereal) one chooses to represent the
positions is irrelevant form a mathematical or calculation standpoint,
unless one gives special weight to purely astrological considerations,
such as where the zodiacal signs should begin or end, a consideration
that for many astrologers (including myself) is of little interest.
A "fixed" sidereal reference frame is no different than what is assumed
about the moment of birth or the birth chart, the concept of "radix",
the radix moment having a different weight than all the others and used
as the common reference frame for all. The radix space and time
coordinates are the basic reference frame in Astrology.
Is astrological analysis (or, for that matter, the analysis of a human
life) a question of anything against anything or is it by necessity
structured around certain "privileged" or meaningful events?
The symbolical link between the concept of "sidereal" (i.e. fixed in
time and space) and the concept of "radix" provides the framework to
understand the different possibilities; one can categorize the types of
events being compared --i.e., birth against anything else, a human
biography, a process, or simple unrelated events. For example,
one can think of:
1-) precession-corrected positions when one date or chart is seen in reference or with respect to the other (the radix)
2-) tropical-only positions when both are seen comparatively in
reference to themselves only (in equal or "democratic" terms, giving
the same weight to the 2 moments)
3-) a traditional sidereal zodiac when both are seen in reference to
something else that includes both. The traditional sidereal zodiac is
especially useful when one is comparing 3 or more independent dates or
These may be more philosophical considerations that are not related
directly to this discussion, but I can see now why I feel that a better
understanding and practical application of precession, as opposed to
the trivial, boring discussion of competing zodiacs-- is so immediately
vital and appealing or important to me.
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.
--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
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.)
one works in a sidereal reference frame, 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 planet 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?
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.
Juan Antonio Revilla
San José, Costa Rica