31
Martin
Sorry, I've lost you. You said you favoured including secondary motion for the significator as well as the promissor, when calculating directions. If the significator (e.g. Moon) has completed 75% of it's semi-arc at birth, and Jupiter, for example, has only completed 45% of its own semi-arc, Jupiter must move 30% more along its own semi arc before it gets to where the Moon was at birth. But if, in the meantime, we've allowed for Moon's secondary motion (while Jupiter is catching up), but not Moon's primary motion (because it is the significator), then when Jupiter makes a direction to Moon, Moon will have moved by just over 1? on the ecliptic (depending on length of the daytime, etc), and will thus have retrograded by something a bit more or less than 1? in its mundo position (relative to meridian and horizon). It would thus have completed less than 74% of its semi-arc (less than it had at birth) when the direction by promissor Jupiter was achieved. That's why I thought we had to leave the secondary motion of the significator out of our calculations. What have I misunderstood?
Thanks
Graham

32
Graham,

I see now where we have misunderstood each other. Let me try to exemplify the approach I favour, using zodiacal directions for simplicity's sake (the principle is the same even when including latitude):

In my chart, the natal Moon is at 18?56' Libra in the 1st house, i.e., between the IC and the Asc. In the usual method for finding the Moon's (zodiacal) nocturnal semi-arc, the Moon is imagined to be stationary at this point, and the NSA is simply the time passed between its lower culmination (18?56' Libra on the IC) and its rising (18?56' Libra on the Asc), expressed in degrees of RA passing over the meridian. The Moon's natal position is then defined relative to this semi-arc.

But if we look to see when the Moon was really conjunct the IC prior to birth, we find that it was at 14?35' Libra; and when it rose some time after birth, it was at 19?54' Libra. The Moon's NSA can therefore be calculated as the time between these two points (14?35' Libra on the IC and 19?54' Libra on the Asc), again expressed in degrees of RA passing over the meridian. This semi-arc is longer than the one above, and the Moon's natal position (which remains unchanged at 18?56' Libra) relative to it will differ somewhat.

Once again, the principle will be the same if we include latitude (and my experience suggests that we should). I hope this example makes my intentions clearer.

33
Martin
I can vaguely make out that there's a logic in what you're proposing, so maybe in a while it'll come clear.
I'm trying to think how what you're saying translates to actually looking at the sky, or to looking at a modeled sky in an astronomy program. I think it still means that (in my example) we would consider the direction of Jupiter to Moon to be accomplished when Jupiter arrived a bit before (in local space) the place where the the Moon was at birth. This still bothers me, so for now I think I'll stick to the angles as significators... Looking forward to you book on primaries !
Graham

34
Graham,
I can vaguely make out that there's a logic in what you're proposing, so maybe in a while it'll come clear.
I hope so. I made it as clear as I could... :???:
I'm trying to think how what you're saying translates to actually looking at the sky, or to looking at a modeled sky in an astronomy program.
That is exactly what I want us to do, and that means using the actual rising, setting and culmination times of the planets for calculating their semi-arcs. If we use those times, we are in fact taking secondary motion into consideration.
I think it still means that (in my example) we would consider the direction of Jupiter to Moon to be accomplished when Jupiter arrived a bit before (in local space) the place where the the Moon was at birth.
Well -- no. Actually, Jupiter will never arrive at the place where the Moon was at birth. It will merely arrive at a point in its own semi-arc which we decide corresponds to the natal place of the Moon, and my point is that for both the semi-arcs (that of the Moon and that of Jupiter), we should use the real rising, setting and culmination times. (Rumen Kolev's software, which was where this sub-topic began, does this only for the promissor, and that is what I objected to.)
Looking forward to you book on primaries !
Thanks. :)

35
Martin
Thanks for clarification. It would help me to try to specify how this could be worked out in the sky or with an astronomy program. This is laborious, but I hope correct. Part of the trouble is trying to think in terms of time rather than of space:

Suppose a direction of Jupiter (promissor) in III to Moon (significator) in I (i.e. both between IC and ASC):
A- find time of Moon's lower culmination
B- find time of Moon's rising
C- subtract A from B to get time of Moon's total semi-arc between lower culmination and rising
D- subtract A from natal time to get time-length of natal semi-arc
E- divide D by C to get percentage equivalent of natal arc time in relation to total semi-arc time
F- find Jupiter's lower culmination time
G- find J's rising time
H- subtract F from G to get time of J's total semi-arc between lower culmination and rising
I- work out time-period corresponding to same percentage (E) of J's total semi-arc time (H) as represented by Moon's natal arc time (D) in relation to Moon's total semi-arc (C) (HxE/100)
J- convert this time period (so many hours, minutes and seconds) into years using used your favoured key: hey presto, you've got the date of the direction!
OK?
Thanks
Graham

36
Martin
Me again. In my example above, can we use setting time to rising time(instead of lower culmination to rising) to work out the semi-arc which we're looking for a proportion of? i.e. semi-arc of the whole day or night period, and not just half of those periods? This would help when looking for interplanetary directions which cross the meridian, but would it cause different values for the MC and IC depending on whether we're using time-based or space-based arcs (and by impliaction, house sytems)?
Thanks for any illumination.
Graham

37
Graham,

As far as I can see, your steps A-J seem to be exactly what I am suggesting. I am glad we understand each other at last! :)

If we include secondary motion, which is not entirely uniform, using whole diurnal/nocturnal arcs rather than semi-arcs could cause a slight difference. But this is not really to do with different house systems. The proportional semi-arc method of directions is the same irrespective of which system of house division one employs. (The Placidus house system is based on this method of direction, not the other way around. Before Placidus, astrologers directed by the same method while using house systems such as Alcabitius or Porphyry.)

38
Martin
Thanks for clarification. This remark of yours is interesting:
The Placidus house system is based on this method of direction, not the other way around. Before Placidus, astrologers directed by the same method while using house systems such as Alcabitius or Porphyry.
In another thread in this forum, "planetary hours calculator", Andrew Bevan argues that since planetary hours are Placidean, they should only be used if you use Placidus houses. Otherwise he feels that the houses you use (e.g. Regio) should be bisected to get your own "house-compatible" "hours". (Hope I've summarised fairly).

I thought when reading this that it was not right, and now I understand why. Planetary hours are what Placidus houses are based on, not the other way around. Their logic is very much the same as the logic behind primaries - the hours are based on the primary day and night temporal arcs of the sun.

As for including secondary motion, I've worked out that we can easily make a rough "rule-of-thumb" adjustment for the Moon's directions (the ones which vary most, of course) :
Use your favourite program to calculate primary-motion-only directions (Solar Fire or whatever: I like to use one with parallax) and adjust the hit dates as follows:
- if Moon is promissor, add 1 yr per 27 yrs, 6 months per 14 yrs, 3 months per 7 years;
- if Moon is significator, subtract as above.

Graham

39
Graham,

Yes -- Ptolemaic directions and planetary hours are both based on diurnal and nocturnal (semi-) arcs, and Placidus (like some others before him) took this as a basis for house division. Regiomontanus, reading Ptolemy differently (and wrongly), invented a new model of directions to suit the 'rational method' of house division; but as far as I know, he left planetary hours alone.
As for including secondary motion, I've worked out that we can easily make a rough "rule-of-thumb" adjustment for the Moon's directions (the ones which vary most, of course) :
That's very useful. Thanks! :)

40
Ptolemaic directions and planetary hours are both based on diurnal and nocturnal (semi-) arcs, and Placidus (like some others before him) took this as a basis for house division. Regiomontanus, reading Ptolemy differently (and wrongly), invented a new model of directions to suit the 'rational method' of house division; but as far as I know, he left planetary hours alone.
This is a fascinating discussion.

However, I'm confused, because what you've written above appears to contradict what's been written elsewhere by Mike Wackford or Rudiger Plantiko, who seem to think that the Placidus method of house division reflects Ptolemy's ideas about domification.

From your previous comments, I take it you prefer the methods of Porphyry or Alchabitius? Is this correct?

41
Hello Andrew,
However, I'm confused, because what you've written above appears to contradict what's been written elsewhere by Mike Wackford or Rudiger Plantiko, who seem to think that the Placidus method of house division reflects Ptolemy's ideas about domification.

From your previous comments, I take it you prefer the methods of Porphyry or Alchabitius? Is this correct?
Personally I tend to favour Alcabitius on purely empirical grounds, but from the textual evidence there seems little doubt that Ptolemy had equal houses in mind. This (if I may quote myself, from another thread) is how Ptolemy defines the suitable places (houses) for the apheta/hyleg in Tetrabiblos III.10 (Robbins's translation, slightly edited to make it more literal):
'the twelfth part [Ptolemy's usual synonym for 'zodiacal sign'] surrounding the ascendant, from five degrees above the actual horizon up to the twenty-five degrees that remain, which are rising in succession to the horizon; the part sextile dexter to these 30 degrees, called that of the Good Daemon; the part in square, the mid-heaven above the earth; the part in trine, called that of the God [?]'
There is certainly no quadrant system, Placidean or otherwise, described in the Tetrabiblos. I don't have a problem with that, however, as I am not a Ptolemy-worshipper. :D But Placidus was determined to read all his inventions (houses, secondary directions, mundane aspects, etc) into Ptolemy's text. That's what theological training does to you! ;)