Skyscript Astrology Forum

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Juan wrote: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).

I think most simply aren't aware of the issue, which only affects the Moon. I remember that Placidus writes somewhere that the Moon's position ought to be corrected for parallax, but in his published charts it seems not to be. I suppose in the 17th century it was a question of how much trouble you wanted to go to for a correction of (generally) less than a degree. Today, of course, parallax correction is just a mouse click away.

To me, the topocentric nature of astrology is obvious. Although we now know the earth to orbit the Sun rather than vice versa, most of us haven't switched to heliocentric astrology, because we think the important thing is the apparent motion (hence we also bother about things like retrogression). But surely it would be very odd to say that the important thing is not the actual (heliocentric) motion, nor the apparent motion as observed from where we are (topocentric), but rather the apparent motion as it would be if we were located in the centre of the earth (geocentric)?

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.

Yes, granted.

I haven't the time right now to study the Abu Ma'shar chart in any detail, but please note that the planetary positions may very well have been taken from different tables: Indian sidereal ones as well as Byzantine tropical ones! That sort of thing did happen in medieval Arabic astrology (as fine an example of the unwitting use of tables as you will find), although I can't say for certain it is what happened here. Varuna's comment seems to suggest it could be the case, though.

Martin Gansten wrote:... please note that the planetary positions may very well have been taken from different tables: Indian sidereal ones as well as Byzantine tropical ones! That sort of thing did happen in medieval Arabic astrology (as fine an example of the unwitting use of tables as you will find), although I can't say for certain it is what happened here. Varuna's comment seems to suggest it could be the case, though.

Yes. Thanks for your comments. According to Pingree in "Dictionary of Scientific Biography", Abu-Ma'shar produced his Zij al-haz?r?t (book of tables) "on the alleged basis of a manuscript said to have been buried at Isfahan before the Flood", which turned out to be a mixture of Indian, Persian, and Greek elements.

Varuna wrote:Regarding Abu-Ma'shar, some of those first list planet placements are almost identical to the zodiac I use, and some of them are different. Not sure if that is relevant here.

Thanks, Varuna. What ayanamsa/zodiac is that?

According to Pingree, the "antediluvian" Zij used/produced by Abu-Ma'shar was based on mean motions of the planets computed by the indian method of the yuga and by using indian parameters. His prime meridian and the parameters for the planetary equations were also indebted to indian sources, but his planetary model was ptolemaic. So his planetary positions are evidently sidereal/indian even though he uses a ptolemaic model for the calculation... a real astronomical hot-podge.

Juan

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varuna2 wrote:What basis of calculation were you using to calculate the planet positions, since your placements of the Sun, Moon, Mercury, Venus, and Mars differ from the Tropical?

Thanks for your reply. But the positions I calculated are plain tropical and agree with those calculated by David Pingree (you can see the "modern computation" list in Pingree's article in the link I gave). There seems to be a confusion between julian and gregorian calendars in your positions, and the difference has been applied in the opposite direction.

Please check your sources and we will continue the exchange.

Juan

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varuna2 wrote:Some of the original planet placements now are in between the 2 zodiac options. Maybe someone made a compromise?
The Sun, Mercury, and Saturn fit that ayanamsha.

I'm not sure which ayanamsa you mean. The Lahiri and K ayanamsas seem to fit the positions of Saturn and Mercury, while Jupiter, the Sun, Mars, and Venus fit best the Raman or the Sasanian zero point (the same of the "tables of the Shah" which were one source used by Abu-Ma'shar).

One single example doesn't prove anything, but I feel the point is made that ancient astrologers used very unreliable planetary positions, with typical errors of several degrees. In this case we can see that the positions are sidereal even though the world-view is tropical (imagine the errors in the Aries ingresses!), and the positions of Mercury and Saturn are inconsistent with the others.

Juan