Most common way to progress the MC in longitude?

1
Hi,

in my home country in europe we almost exclusively progress or direct the MC on the equator in right ascension. Therefore I like to learn more about how progressing the MC in longitude is done?

What is the most common (right?) formula to progress the MC and houses with true solar arc in longitude?

There are three possible formulas:

Method 1:
1.1. Measure the true solar arc on the ecliptic in longitude.
1.2. Add this arc in longitude to the MC in right ascension. *
1.3. From this progressed MC in right ascension (RAMC) calculate the houses in longitude.

Method 2:
2.1. Measure the true solar arc on the ecliptic in longitude.
2.2. Add this true solar arc in longitude to the MC in longitude
2.3. Convert this progressed MC in longitude to right ascension.
2.4. From this progressed MC in right ascension (RAMC) calculate the houses in longitude.

Method 3: (formerly wrong written 'method 2', see below):
2.1. Measure the true solar arc on the ecliptic in longitude.
2.2. Convert this true solar arc in longitude to right ascension
2.3. Add this true solar arc in right ascension to the MC in right ascension
2.4. From this progressed MC in right ascension (RAMC) calculate the houses in longitude.

* Adding an arc measured in longitude to a MC in right ascension seams not right to me.

Astrology programs that calculate Secondary Progressions or Primary Directions in true solar arc in longitude:
Method 1: Placidus 7 with Primary Directions
Method 2: Janus 4.3 with Secondary Progressions
Method 2: Solar Fire with Secondary Progressions and van Dam Primary Directions
Method 3: Don't know any program that calculates method 3. Is there one?

Here is an example horoscope of Queen Elizabeth from Astro-Databank:
http://www.astro.com/astro-databank/Eli ... of_England

Natal chart: AC 21?22'44" Capricorn, MC 25?32'48" Scorpio

Secondary Progressions with true solar arc in longitude for April 21. 2015:

Method 1 (Placidus 7):
Progressed: AC 21?57'52" Gemini, MC 16?10'51" Aquarius.

Method 2 ('Solar Fire' and 'Janus'):
Progressed: AC 26?38'19" Gemini, MC 20?58'40" Aquarius.

Chris
Last edited by Chris Meyer on Thu Dec 03, 2015 4:17 am, edited 22 times in total.

2
For progressions and regressions, the Angles/Cusps should move according to Right Ascension as that will introduce smaller orbs than using Longitude.

...and I realize this doesn't answer your question. ;)

4
Hi there,

I'm having trouble understanding what you are trying to do.. Are you talking about Primary Directions? Could you give us an example of what you are trying to calculate?


Regards,
Jo?o Ventura

5
Hi Jo?o,

both secondary progressions and primary directions. In secondary progressions the angles are directed primary anyway.

I suppose that for secondary progressions MC and house progression / direction with True Solar Arc in longitude is quite common in USA. I found out also that "True Solar Arc in longitude" is used for primary directions called "Wim van Dam" method: www.astrosoftware.com/WimPrimaries.htm

I added an example horoscope with secondary progressions to my initial post. MC and AC are progressed / directed with the two different methodes I mentioned. Hope that helps to make it clearer.

6
Hi Chris,

I have a question too. It could be part of what you want to find out.

When one compares the angles of an solar arc chart to the angles of a progressed chart done with solar arc in long (for the same time) the MC's are the same but the AC's differ.

example for queen elizabeth:
1th of July 2015 Solar Arc AC 15?05 aries and progressed solar arc in long AC 25?00 gemini

Why do the AC's differ?

8
Hi there Chris,

I don't know much about true solar arcs and secondary directions since I don't use them in my own practice.

But if it is similar to how to "primarily" direct a planet to a meridian (such as MC), I use something like your 2nd formula. First you must convert the planet's position from ecliptical to equatorial coordinates, and then to a subtraction to get the arc of direction (eg. RA Promissor - RAMC).

In my opinion, the 1st formula is mixing potatoes with apples. You should not add something measured in ecliptical degrees to something in equatorial degrees since they are different referentials. That is why we must project a planet's ecliptical lat/lon to its respective position in the equator (ra/decl) and work in equatorial coordinates. And we do this because, for primary directions at least, the "rule" is "one degree of RA equals aprox. one year".

I'm being over-simplistic, but I hope this makes sense for your case of solar arcs and secondary directions.


Regards,
Jo?o Ventura

9
Hi Jo?o,
I use something like your 2nd formula. First you must convert the planet's position from ecliptical to equatorial coordinates, and then to a subtraction to get the arc of direction (eg. RA Promissor - RAMC).
This is a well known method the astrologer 'Placidus' invented. In the astrology program 'Morinus' it is called 'True Solar Equatorial Arc'.

My question is about 'True Solar Ecliptical Arc'. This is a modern invention mostly used for Secondary Progressions in USA and for Wim van Dam Primary Directions.
In my opinion, the 1st formula is mixing potatoes with apples. You should not add something measured in ecliptical degrees to something in equatorial degrees since they are different referentials.
Yes that is just what I'm thinking too.

Thank you for this valuable assessment of an astrology programmer.

Chris

10
jventura wrote:In my opinion, the 1st formula is mixing potatoes with apples. You should not add something measured in ecliptical degrees to something in equatorial degrees since they are different referentials.
I don't see it that way. I see this as the correct way of using the true solar arc. You're not mixing up different referentials here. This becomes clear if you view the solar arc in longitude as "part of a year" and if you view the arc of the MC in R.A. as "part of a day". So you are actually dealing with different temporal arcs.

Then I must say that Wim van Dam uses the method of adding the true solar arc in longitude to the MC in longitude.

And most traditional astrologers are not so interested in the secondary progressions (a rather recent invention by Placidus) and direct all points using Naibod or some other key.

11
Hi Ruud66,

did you read my intial post of this topic and recognised the difference between method 1 and method 2?

As written there both common astrology programs "Solar Fire" and "Janus" are calculating Secondary Progressions with True Solar Arc progressed MC like method 2.

In "Solar Fire" you find this option in Menu / Preferences / Progs/Dirns / Chart Angle Progression: "SA in Long".

In Janus: Menu / Calculate / Transists/Directions/Progressions.../ Options / Progressed MC: "True SA Long".

Also Wim Van Dam Primary Directions you mentioned are based on method 2 (calculated by "Solar Fire" and "Sirius").

So I suppose method 2 is the most common way to progress or direct the MC in True Solar Arc in longitude. If its the only correct way to do it I'm not 100% sure about.
Last edited by Chris Meyer on Thu Jul 16, 2015 2:05 am, edited 1 time in total.

12
Chris Meyer wrote:did you read my intial post of this topic and recognised the difference between method 1 and method 2?
Hi Chris, of course I read your post, but I only said some things I wished to react to. In the first method the solar arc in longitude is directly added to the RAMC, in the second method the solar arc is added to the RAMC in right ascension.
As written there both common astrology programs "Solar Fire" and "Janus" are calculating Secondary Progressions with True Solar Arc progressed MC like method 2.

Also Wim Van Dam Primary Directions you mentioned are based on method 2 (calculated by "Solar Fire" and "Sirius").
I don't know much about the different calculation programs. I always calculate progressions etc. in my own way using a spreadsheet I programmed myself.
One thing I know for sure: Van Dam doesn't use method 1 or 2.

{edit} this has been corrected in the first post by Chris; method 2 is used by Van Dam.{/edit}

He uses the method I outlined in my previous post. I know this because I have the original article in which he published his system of primary progressions for the first time. This was in the Dutch astrological magazine "Spica" somewhere in the 1980's.
So I suppose method 2 is the most common way to progress or direct the MC in True Solar Arc in longitude. If its the only correct way to do it I'm not 100% sure about.
I don't think there is a "correct" method of progressing the angles. This technique of progressing the angles in the secondary progressed chart is in itself a modern mutation of primary directions and using that in conjunction with the secondary progressed chart is a questionable practice. If anything is mixing potatoes with apples then this is it.

I'm sorry if my answer disappoints you, as I realise I can't offer any clear-cut answers.
Last edited by Ruud66 on Thu Jul 16, 2015 4:37 pm, edited 2 times in total.