Skyscript Astrology Forum

In another thread, in another forum (Nativities & General Astrology) -
http://skyscript.co.uk/forums/viewtopic ... c&start=15

this statement -

If we apply the horizon coordinate system it makes sense to use charts that correctly display the Moon's position in this system, with parallax. As we know, the geocentric (centre of the Earth) ecliptic coordinate system in a two-dimensional representation shows the Moon's geocentric position without parallax.

was answered by me thus -

johannes susato wrote:If this were true, then the AC of the paranatellonta would differ too, because the apparent horizon cuts the ecliptic not in the same point as the true horizon. But as the paranatellonta have no differing AC to my knowledge, it seems, that paranatellonta are based upon the true level (horizon) cutting the midth of the earth, and then the displaying of the Moon's parallax would be in-correct becaue in the center of the earth there is not any parallax.

Now I am very eager to know the horizon which paranatellonta are computed to really.

Is the horizon of Paranatellonta
the true level (true horizon) or
the apparent horizon (eventually considering even the depression or dip of the horizon)?

I would like to thank you already in advance for all answers.

Johannes

Hello Johannes
I'd always assumed that paranatellonta were, unless otherwise specified, measured on the true horizon, just as other astrological factors usually are. If you wanted to use the apparent horizon for them, you'd logically have to use it for all the rising chart factors (planets, ascendant degree...), and make that clear.
Parallax is a different issue than apparent horizon - it depends on the distance of the object, not intrinsically on the nature of the horizon. It involves choosing to locate an object in relation to it's background (e.g. the moon in relation to fixed stars, galactic coordinates or to an equatorial projection in space like the vernal point), not from the centre of the earth but from where you are, on the surface. That position is not usually corrected for apparent horizon, I think, but that doesn't mean it's measured from the centre of the earth: you just use lunar parallax, if you want, to take account of the Moon's proximity. Other objects are too far away for it to make any significant difference for astrology, whereas all rising and setting factors will be equally affected by the apparent horizon.
I trust someone will correct me if I've got all this wrong.
Graham

Graham Fox wrote:Parallax is a different issue than apparent horizon - it depends on the distance of the object, not intrinsically on the nature of the horizon. It involves choosing to locate an object in relation to it's background (e.g. the moon in relation to fixed stars, galactic coordinates or to an equatorial projection in space like the vernal point), not from the centre of the earth but from where you are, on the surface.

Yes, lunar parallax (or lunar horizontal parallax, as it is also called -- a bit of a clue there) depends on the difference between the geocentric and the topocentric perspective; but these two perspectives give rise to two slightly different horizons, so there is a connection. Only the Moon is close enough to us for the difference between the geocentric and topocentric horizons to matter; furthermore, the difference is at its greatest when the Moon is close to the horizon and is non-existent when the Moon is on the meridian.

For all other purposes, such as determining the ascendant or the paranatellonta, the distances involved are so great that the earth can conveniently be regarded as a point in space, which is what the geocentric perspective amounts to, rather than a body; and that is what is typically done in astrology. To me, however, it seems clear that the astrological world-view is fundamentally topocentric (or perhaps we should say topo-chrono-centric?), and I definitely get better results when correcting the Moon's position for parallax. I say this as someone with a first-house Moon myself.

Martin, feel free to point and laugh at me if I'm being a little dim here, but what about when the Moon is below the horizon? I'm reading the technical description of parallax but my days as a mathematician ended in high school and my head is quite sore now.

david cochrane did some research on parallex moon that he talks about in a little booklet he released in 2002 called 'astrolocality magic'. here is an article that touches on some of his thoughts.

"In research that I have done in the past amazingly the parallax-corrected Moon seemed to not work as well as the plain old Moon and this surprised me. I suspected that the parallax-corrected Moon would be more accurate because it is the position of the Moon from the person's point of view."

http://www.astrosoftware.com/What%20is%20Parallax.htm

Martin Gansten wrote:Yes, lunar parallax (or lunar horizontal parallax, as it is also called -- a bit of a clue there) depends on the difference between the geocentric and the topocentric perspective; but these two perspectives give rise to two slightly different horizons, so there is a connection. Only the Moon is close enough to us for the difference between the geocentric and topocentric horizons to matter; furthermore, the difference is at its greatest when the Moon is close to the horizon and is non-existent when the Moon is on the meridian.

The "true" horizon is geocentric, and is equivalent to working without parallax correction, the apparent horizon is topocentric and is the equivalent of working with parallax correction. The "horizontal" parallax is the maximum parallax at the horizon and is used sometimes to calculate the actual parallax, which is a function of the zenith distance. Parallax becomes zero only at the zenith, not when the planet is at the Meridian.

Juan

Martin Gansten wrote:To me, however, it seems clear that the astrological world-view is fundamentally topocentric

Clearly, parallax means that Moon's observed position against the background of the planets and stars is substantially different from the geocentric position - but there are other effects when bodies are rising or setting.

The first is refraction. When the sun is observed to be half risen, so that the centre of the sun is seen to be on the horizon, the light from the sun is being bent around the earth by the earth's atmosphere. The centre of the sun is then actually more than half a degree below the geocentric horizon, meaning that the sun has still to rise and it is astrologically still night time and a chart drawn up at this time would be considered a night chart.

And then there is what celestial navigators call 'height of eye', which is how high your sensible horizon (a plane parallel to the geocentric horizon which goes through your eye) is above the geoidal horizon (a plane parallel to the geocentric horizon which is tangent to the surface of the earth). Clearly, if you are perched on top of a 10,000 ft mountain overlooking the sea, the Sun is going to be observed to rise a lot sooner than it would if you were standing at the sea shore...

The same is true for the Moon, planets and stars of course, except that absorption of light by the atmosphere means we don't actually see them when they are on or just above the visible horizon. The altitude (angle above the horizon) a body has to rise before we actually see it depends upon its brightness. The rule of thumb is that this altitude in degrees is equivalent to the visual 'magnitude' of the body, so a magnitude 3 star will not be seen (under ideal conditions) until it is three degrees above the horizon. Are stars and planets considered to be below the horizon until they are visible and so above the horizon?

Geoffrey

Konrad wrote:Martin, feel free to point and laugh at me if I'm being a little dim here, but what about when the Moon is below the horizon? I'm reading the technical description of parallax but my days as a mathematician ended in high school and my head is quite sore now.

I'm certainly not laughing; I found these things hard to learn myself (my spatial thinking is rubbish). Even if the Moon is below the horizon, its position against the background of the zodiac will differ depending on whether it is calculated from the vantage point of the centre of the earth (geocentric) or from that of a particular place on the surface of the earth (topocentric).

Imagine a line being drawn from the earth's core through the Moon and then further into space. Then imagine a second line bring drawn from your home town through the Moon and beyond. The two lines will converge at the position of the Moon but end up in slightly different places, which is why the Moon will appear to be in one degree of the zodiac geocentrically, and in another degree topocentrically.

Juan wrote:Parallax becomes zero only at the zenith, not when the planet is at the Meridian.

Yes, quite right, as far as coordinates go. I wrote on the run and had in mind rising and culmination times (a result of working intensively with primary directions). Parallax correction will affect the Moon's rising and setting time but not its culmination.

Geoffrey wrote:Clearly, parallax means that Moon's observed position against the background of the planets and stars is substantially different from the geocentric position - but there are other effects when bodies are rising or setting.

Yes, of course. One major difference between parallax and refraction as I see it, though, is that refraction is entirely a visual phenomenon (partly dependent on extraneous factors like weather conditions), whereas parallax is a mathematical difference, equally valid when the Moon is not actually visible on or above the horizon.

Martin Gansten wrote:

Konrad wrote:Martin, feel free to point and laugh at me if I'm being a little dim here, but what about when the Moon is below the horizon? I'm reading the technical description of parallax but my days as a mathematician ended in high school and my head is quite sore now.

I'm certainly not laughing; I found these things hard to learn myself (my spatial thinking is rubbish). Even if the Moon is below the horizon, its position against the background of the zodiac will differ depending on whether it is calculated from the vantage point of the centre of the earth (geocentric) or from that of a particular place on the surface of the earth (topocentric).

Yes, of course. One major difference between parallax and refraction as I see it, though, is that refraction is entirely a visual phenomenon (partly dependent on extraneous factors like weather conditions), whereas parallax is a mathematical difference, equally valid when the Moon is not actually visible on or above the horizon.

Right thanks. Good description. Your reply to Geoffrey clears it up; I thought Parallax was entirely visual hence me not understanding why it would be effective below the horizon.

Geoffrey wrote:

Martin Gansten wrote:To me, however, it seems clear that the astrological world-view is fundamentally topocentric

parallax
refraction
'height of eye'
Geoffrey

It is a myth to think that --since the time astronomical tables were developed-- astrologers were "sky watchers" because the historical evidence shows that they were actually "table users", and this is still true today.

Conventional astrological tools are not based on the observation of the sky but on calculations by means of tables, and the ancient and medieval tables (or the astrologer's calculations) were in many cases inaccurate, particularly in the position of the Moon. This can be easily proved by looking at the hundreds of ancient or medieval horoscopes extant: the lunar positions are as a rule wrong by several degrees.

A direct result of this is that the correlations with the actual planets in the sky are often very thin and always indirect: the correlations are with discrete coordinates on a chart that in most cases have no correspondence to anything observable in the sky.

Juan

I agree with what you say, Juan, though I'm not sure if any of it was meant as a reply to me (since you quote me), and if so, how.

Also, I think we should acknowledge that although astronomer-astrologers have been table-users since Babylonian times, the tables were based on (and occasionally corrected on the basis of) observation. Although reality often fell short of the ideal, the tables were always meant to stand in for actual observation.

Martin Gansten wrote:I agree with what you say, Juan, though I'm not sure if any of it was meant as a reply to me (since you quote me), and if so, how.

I was a little struck by the "topocentric worldview" assertion, not because I think it is wrong, but because it feels so contradictory or paradoxical, particularly in the light of lunar parallax. Your assertion dramatized in my mind that astrologers think or believe one thing (the topocentric world-view) but do something different to what they think they are doing (the geocentric perspective).

Also, I think we should acknowledge that although astronomer-astrologers have been table-users since Babylonian times, the tables were based on (and occasionally corrected on the basis of) observation. Although reality often fell short of the ideal, the tables were always meant to stand in for actual observation.

But the truth is that usually they didn't, so this illustrates what I'm saying: astrologers just assume that they did. The same can be said of the majority of astrologers today, who are unaware of the effects of lunar parallax.

I was thinking of providing at least one example and have been looking at the horoscope of Abu-Ma'shar published by David Pingree in "Historical Horoscopes", Journal of the American Oriental Society Vol. 82, No. 4 (Oct. - Dec., 1962), p. 487. Unfortunately Pingree does not provide a reproduction of the original and he doesn't mention the Asc. or MC degree, so I was wondering if anybody in the forum knows of a source for the original?

Anyway, the horoscope data is given as 10 Aug 787 at noon at or near Balkh. According to Pingree "the date of his birth is known from a horoscope in his Kit?b ahk?m tahwil sind'l maw?lid 3,l" (this book is apparently the same as "Book of Judgments About Nativities", and "the birth is said to have taken place in a city whose latitude is 36 degrees N. Ab? Ma'shar, therefore, either was born somewhere south of Balkh or used a fictitious latitude for his native city because of its convenience in computations". He uses 3 different sources:

A = arabic version in Escorial 917
G = greek version in vaticanus graecus 191 and parisinus graecus 2507
L = latin (from the greek) in Claudii Ptolemaei Quadripartitum enarrator ignoti nominis, Basileae (1559) p.248

the whole page from Pingree can be seen scanned here:
http://www.jstor.org/discover/10.2307/5 ... 1580917017

the planetary positions are given as:

Saturn = 23,26 Aquarius
Jupiter = 20,26 Capricorn (20,16 Cap in L)
Mars = 10,29 Leo
Sun = 15,59 Leo (15,57 Leo in G -- 11,57 Leo in L)
Venus = 2,54 Libra
Mercury = 22,07 Leo
Moon = 12,43 Taurus (12,40 Tau in A)

Presumably Pingree used the position of the Moon to pin-point the date, but this implies an error of at least 4 degrees in the position of the Sun.

Here is the modern computation for comparison (12h apparent solar time is used for reference only - I use for Balkh 36n46/66e54):

Saturn = 0,23 Pis r
Jupiter = 24,25 Cap r
Mars = 13,55 Leo
Sun = 20,14 Leo
Venus = 6,21 Lib
Mercury = 28,41 Leo r
Moon = 10,13 Tau
MC = 20,14 Leo
Asc = 12,56 Sco

Has anybody seen an independent documented version of this horoscope?

NOTE 1: the error --excluding the Moon-- is respectively -6.57, -3.59, -3.26, -4.15, -3.27, -6.34... which suggests sidereal positions with the zero point around 450 or 500 AD. If we assume that the position of the Sun is (sidereally) accurate, the error in the position of the Moon would be 6,33' (or viceversa).

Juan