Martin Gansten wrote:... there is no necessary correlation between house division and method of direction. (...) Makransky invented a directional method based on the Alcabitius house system, but that was entirely untraditional. (Plantiko, for those who read German, did the same.)
This reminds me of the discussion some time ago,
http://www.skyscript.co.uk/forums/viewt ... c0dbc1cd3e page 4 of that thread.
Martin Gansten wrote:Ed F wrote:This statement confuses me. Various circles of position (various definitions, depending on domification model) and proportional semiarc positions give different results for directions.
The phrase
depending on domification model rather begs the question.

There are any number of house systems, but only two historically practised methods of (full-blown) primary direction; and before the 15th century there was only one in common use, namely, Ptolemy's semi-arc method (later to become the basis of the Placidus house system). Ptolemy's method was used by generations of astrologers who simultaneously employed whole-sign houses, equal houses, Porphyry houses and/or Alcabitius houses as their 'domification model'. The idea that house system and method of directions should be somehow related was apparently alien to them.
zoidsoft wrote:If the arc of direction is the same in both directions, then how is the measurement going to be different? I'm defining here that point A arcs to point B, to measure from B to A should be the same. If latitude changes, then the points change.
Perhaps the following example will clarify the difference a bit.
Natal chart
Marseille, France 5?24?E, 43?18?N -
1 january 2000, 0:00. Universal Time 23:00 (31 dec 1999).
Sidereal Time 6h01m18s.
Source
www.astro.com ? free chart selection.
Secondary motion of the planets isn?t taken into account in this example, nor is latitude.
Imagine Venus and Jupiter being positioned as follows:
Venus on cusp XII ? 4?42? Virgo
Jupiter on cusp XI ? 4?22? Leo
Considering the following four situations.
Forwards in time after birth:
1- Jupiter directed to cusp IX gives a ?Placidian? in zodiaco square to cusp XII and thus to Venus.
2- Venus directed to cusp VIII gives a ?Placidian? in zodiaco square to cusp XI and thus to Jupiter.
Backwards in time before birth:
3- Jupiter directed backwards to cusp III gives a ?Placidian? in zodiaco square to cusp XII and thus to Venus.
4- Venus directed backwards to cusp II gives a ?Placidian? in zodiaco square to cusp XI and thus to Jupiter.
The questions are when these positions will take or took place.
1- When cusp IX is at 4?22? Leo.
2- When cusp VIII is at 4?42? Virgo
3- When cusp III was at 4?22? Leo.
4- When cusp II was at 4?42? Virgo.
With a bit trial and error typing different times the following
sidereal times! are found.
hh:mm:ss
1- 10:52:18 (04:50:13 West European Time = UT+1)
2- 14:51:09 (08:48:25 WET)
3- 22:01:19 (16:01:20 WET, 31 December 1999)
4- 02:01:18 (20:00:40 WET, 31 Dec)
Expressed in equatorial degrees the sidereal times are (rounded off to the nearest minute):
1- 163?45?
2- 222?47?
3- 330?20?
4- 30?20?
for the natal sidereal time we get 90?20?
So for the mutual differences in sidereal time degrees we get:
1- 73?25?
2- 132?47?
3- 120?00?
4- 60?00?
These are considered as years according to Ptolemy?s key.
Conclusion: If forwards in time would give the same result as backwards in time, then 1 would be equal to 4 and 2 equal to 3. This isn?t the case because the semi arcs of the planets are different when expressed in equatorial degrees (Sun in 4?Leo gives a longer day than Sun in 4?Virgo)and therefore the results in time are different. When expressed in distances between cusps they are similar (just like days with the Sun in 4?Leo and in 4?Virgo both are 12 'seasonal' hours in length).