17
Petr wrote:Janus calculated incorrectly Alcabitia,he calculated correctly Regio PD(Regiomontanus)-under selection Placidus.
Just as an aside, thanks for confirming that. That is more or less what I told Mark Griffin.

18
Now, I know that this discussion with all these softwares is fantastic and all, but can anyone tell me if the method used by astro.com for calculating the directions to the angles is correct?

I have Solar Fire and do not plan to spend (read it as can not) money on another program, and as we all know Solar Fire does not calculate it correctly (or does it, I obtained same results, but what if both are wrong?).

Thanks in advance.

20
PFN wrote:I have Solar Fire and do not plan to spend (read it as can not) money on another program, and as we all know Solar Fire does not calculate it correctly (or does it, I obtained same results, but what if both are wrong?).
Solar Fire does calculate Placidean in mundo directions correctly. This means that conjunctions and oppositions to the angles are calculated correctly, if you are happy to take the latitude of planets into consideration. Other aspects to the angles are not the normal aspects of astrology (based on distances along the ecliptic), but inventions by Placidus based on proportional semi-arcs.

22
In most types the first step will be converting ecliptic to equatorial positions using the following conversion formulae:
http://en.wikipedia.org/wiki/Ecliptic_c ... oordinates

If you prefer to use ecliptic positions without latitude then these simpler formulae can be used:
sin ? = sin ? sin ?
cos ? cos ? = cos ?

On this website you can also find equatorial positions:
http://www.ephemeris.com/goto.php
Astronomers note (RA) positions in hours, minutes and seconds.
These can be converted to ? ' " by multiplying hrs by 15 and dividing the minutes and seconds by 4 e.g. 21h35m19s = 323?49'45"

These can already be used for Meridian house system based primary directions. The 'MC' in this system is the sidereal time of birth converted to degrees as above. You can use 1?= 1 year or apply a time key which slightly alters the result.

For primary directions based upon Placidus or other house systems like Regiomontanus and Campanus, John Napier's formulae for spherical trigonometry are needed. Based upon Napier's rule for triangles with a right angle we get the following formulae:
cos c = cos a x cos b
sin a = sin c x sin A
sin b = sin c x sin B
cos A = cos a x sin B
cos B = cos b x sin A
Here C is always 90?, A and B are the other angles. a, b and c are the sides opposite to the angles A, B and C respectively.
For our purposes we need the first two formulae in which
A = (90? - Latitude place of birth)
a = declination (of the planet or other point)
We need to find the result for b which is on the equator.
Since I only learned it with these formulae I'm not really familiar with some terminology. The best thing one can do is looking how a house system is discribed and draw it on paper.
This picture makes things clearer:
http://abyss.uoregon.edu/~js/images/star_coord.gif
http://abyss.uoregon.edu/~js/ast122/lectures/lec02.html
In that picture the triangle formed by the letters W V and the glyph for Aries would be the same as the triangle A B C of above. Note that that last point isn't necassarily always 0?Aries.

With this you can find the different lengths of the diurnal or nocturnal 'path' of each planet. The part of the path travelled by the planet divided by the length of the total diurnal/nocturnal path and finally multiplied by 180? leads the way to the Placidus house position. It shows that in fact Placidus is one of the easiest systems.

On the Astrodienst website there is an option that can be used for calculating primary directions based upon Placidus.
http://www.astro.com/cgi/genchart.cgi?&lang=&gm=pu
Free horosopes>Pullen/Astrolog>'Gauquelin sector chart for Prof. Ertel'
These may be slightly different from Placidus but can be used for a start.
First make your natal chart then make a chart for the date you would like to investigate. If you want to see the chart for age 43 convert to hours and minutes and add to your birth time 43 years/degrees = 2h52m.

A simple method can be used by simply calculating the usual ecliptic chart for some hours later after birthtime. The new MC and Ascendant then are compared with the positions in the natal chart. This method would have some value I think because it is based upon the ecliptic which is used in most fields of astrology. The other systems obviously give also another type figure of natal chart. Everybody has their preferences for a particular system based upon different mathematical views so they can use this as additional to or alternative for the natal chart.

I prefer the Meridian method (as additional/alternative) and the 'simple method'. Notwithstanding the historical roots in the 'seasonal hours' of the antique era, I don't feel for Placidus. At the Netherlands' latitude, with most planets in diurnal and nocturnal paths of about 8 to 9 hours. The aspects found by directions occur in a short time after each other but when these planets reach the horizon their paths on the other side suddenly is 15 to 16 hours. I don't like this sudden change. Perhaps Campanus would give a more smooth change, however the differences remain big. I therefore prefer the more equal movement of the Meridian system and the simple method (in which at least the MC moves at more or less regular speed).