Martin and Ed hi,
Thank you both.

In this reply I'm only replying to Martin on his post for the date of: Wed Feb 19, 2025 9:07 pm.
Martin, okay.
Now I understand why the ASC is only found due east twice a day, when 0 Ari or 0 Lib is on top of that degree.
That's great.
This image helped my understanding too: https://physics.weber.edu/schroeder/ua/ ... Sphere.png
--
About me asking: if the MC is the highest point a degree can reach, and the nonagesimal the highest point above the horizon in a given moment, what's the difference?
So, from your explanation I came to understand that the nonagesimal, in a way, is an imaginary point (as no degree can reach it in a given moment in time). If this is the case, why use it anyways? Do you see a logic or a conceptual framework, in which it would remain valuable, for astrological delineation?

You need to change your Solar Fire settings! No, really: if you want a reasonably accurate depiction of what actually happens in the sky, you need to keep the meridian and horizon at right angles.

I'm not sure there's a setting for that in SF. If anyone knows, It would be interesting to hear.

Also: why do you call it "the anti-nonagesimal"? (the 90 degree angle near the MC i presume)

You've got me all excited about armillary spheres. I wonder if I can get a good one on Amazon (or someplace else)

I'll reply to the rest later, short on time as usual.
D.

I'm glad you found some aids to understanding, Dima. To start with terminology, there is in fact already a point traditionally known as pars nonagesima in Latin, or ἐνενηκονταμερίς enenēkontameris in Greek. Both names are given by Firmicus (discussed in Mathesis 8.2.1) and mean 'the ninetieth degree'; but that's counting in zodiacal order. If we should give a name to the equal tenth-house cusp, which is 270 degrees away from the ascendant, I suppose it should be the ducentiseptuagesimal, but that's probably too much of a tongue-twister!

Next, Solar Fire: in my (old) version at least, I can right-click a chart and select Display Options > Proportional Houses Off. Provided I've selected a quadrant-house system, this will set the MC/IC axis perpendicular to the Asc/Dsc axis, the way it is in reality.

Armillary spheres are indeed available online. They may not be precision instruments (unless you are prepared get something very large and very expensive), but they are quite useful to think (and teach) with.

Finally, I wouldn't call the 'nonagesimal' imaginary so much as erratic. Because of the obliquity of the ecliptic, the Asc and Dsc keep moving back and forth along the horizon, which means that the point exactly midway between them (the 'nonagesimal') also keeps shifting, both between the eastern and western hemispheres and up and down with respect to height above the horizon. But that doesn't mean it can't have astrological significance. My experience strongly supports quadrant houses as the most important form of house division, but I wouldn't discount equal houses altogether. If we look at traditional house meanings, some seem to relate to dynamics of rising, culminating and setting, others to aspectual relations, and the latter is what equal houses are based on. They are present in Valens (although he seems overall to have favoured quadrants, at least in theory/principle), in Ptolemy, and in Firmicus. I think it probably means something to have a planet forming a superior square to the Asc degree (= being on the 'nonagesimal'), although that meaning may differ to some extent depending on whether the aspecting planet is in the (quadrant) 9th, 10th, or 11th house.

A fully interactive Demonstrator.

PhoenixNoodleSoup wrote: Sun Mar 02, 2025 2:31 pm A fully interactive Demonstrator.

Thank you, that's excellent. Again, although the heading says 'Motions of the Sun', for our purposes we can ignore the solar disc and focus on the white circle, which is the ecliptic (running down the middle of the zodiacal belt, which isn't shown). We can clearly observe its wobbly motion over the course of a day and night, its rising and setting points on the horizon shifting north and south. The 'nonagesimal' isn't marked but can easily be eyeballed, as it is always midway between the Asc and Dsc points.

Thank you. First let me say I'm an avid and appreciative reader of the forum and your contributions.
I'm especially glad you've mentioned the Zodiacal Belt which (please correct me if I'm wrong) generally extends 8 degrees north and south of the Ecliptic.
Zodiacal positions are usually given in Ecliptic Longitude, which is entirely acceptable in regard to Signs, but not entirely acceptable in regard to Houses.

I have had some difficulty in understanding what it is Dima Gur is actually trying to conceptualize.

I may not understand yet, but I suspect it is in regard to Houses.

I hope this thread is beneficial to Dima Gur and anyone else trying to understand the various astronomical coordinate systems and what they have to do with astrology.

In my opinion astrologers would do well in considering the Ecliptic Latitude of important points (positions of planets, etc.) in regard to House Positions (whatever House system they may use).

Martin:
Some more fragments of replies, given my tense schedule.

Tried to play with proportional houses in my solar fire. It doesn't seem to make any change, for some reason.
Also redrew the chart which was shown but no effect

The animation is great, thank you Phoenix.
How do you spot the MC in the animation? Is the thin white line going from south to north, the Meridian?
If yes, then the point in which that line intersects with the ecliptic (up at the top) should be the MC...

Also, is there a simple explanation of why the Ecliptic wobbles? Its rising and setting points shifting, north and south.
Maybe some animation for that...

About the 90th vs 270th degree. Got it.
And thinking of the nonagesimal as the superior square, does make it easier to understand.

---

Ed, will try to reply to you too, later on.

Phoenix, I remember you from the astro.com forum, Greetings on joining us here.

Hi Dima Gur

Ed, will try to reply to you too, later on.

No problem - when you have time.

Also, is there a simple explanation of why the Ecliptic wobbles? Its rising and setting points shifting, north and south.

The explanation for this comes back to a few factors.

Firstly, consider the obliquity of the ecliptic, previously mentioned. The planes of the ecliptic and the celestial equator are not co-incident. The ecliptic, from the perspective of the celestial equator, is inclined to the equator at around 23.46 degrees (this value, known as the obliquity of the ecliptic, changes over time but extremely slowly). This means that the poles of the celestial equator and the ecliptic are not co-incident. They are separated from each other by the value of the obliquity of the ecliptic.

Secondly, consider the earth's rotation over the course of a day. The earth rotates on its own axis around the poles of the celestial equator once over 24 hours or so. The poles of the ecliptic therefore rotate around the poles of the celestial equator once every 24 hours. Essentially they describe a small circle around the poles of the celestial equator.

It is only when the poles of the celestial equator and the poles of the ecliptic align on the meridian plane that the ecliptic rises exactly due east (which will occur twice a day when either 0 Aries or 0 Libra rises). At other times of the day, when the pole of the ecliptic does not lie on the meridian plane, the ecliptic will rise either towards the northern point of the horizon or the southern point of the horizon.

It's difficult to describe and probably difficult to visualise from a verbal description. I will see if I can do some simple diagrams to explain it visually. Walter Pullen's Astrolog software contains a lot of animation functions which show this quite clearly. Do you use his software at all?

He has posted this animation on the forum before which shows what I am trying to describe. Try and open this in your browser in a new tab or new window by right clicking on the link:

http://www.astrolog.org/astrolog/pic/campanus.gif

In this you can clearly see the impact of the rotation of the celestial sphere on the dynamics of the ecliptic during the course of a day.

To interpret this graphic:

Green line running more less vertically = prime meridian. Note that the MC's movement during the course of the day is vertically up and down the prime meridian. Again this is due to the fact that the poles of the ecliptic and the poles of the celestial equator are not co-incident.

Green curving lines = cusps of Campanus Houses. Their pole is the north and south points of the horizon. (We can see the southern pole in this graphic.)

White line running more or less horizontally = horizon.

Purple curving lines = 12 equal divisions of the ecliptic. These are lines demarcating the twelve equal divisions of the ecliptic, focused on the poles of the ecliptic. These divisions are of course known to us as demarcating the zodiac signs. You can see the diurnal rotation of the planets in the graphic as the rise, culminate and set. In the graphic we can only see the southern pole, but in the northern hemisphere, the northern pole of the ecliptic would be rotating around the north pole of the equator.

The key thing here is to study the movement of the southern pole of the ecliptic which is where the twelve equal divisions of the ecliptic (zodiac signs) meet below horizon. See that this is in a constant state of regular motion about a fixed point. Unfortunately Walter's graphic doesn't mark the southern pole of the celestial equator but effectively this is what the graphic is showing - the movement of the poles of the ecliptic about the fixed points of the poles of celestial equator over the course of a day.

Once you have this fixed in your mind, look at the the east point of the horizon (marked with the red 'E'). Note how the ASC moves into view and out of view as the ecliptic rotates about the fixed point of pole of the celestial equator. This is the phenomenon that you are seeking to understand. When the ASC hoves into view, it is rising south (in the horizontal plane) of the eastern point of the horizon. This means that the signs Libra-Pisces are rising (they have southerly declinations - lie below the plane of celestial equator). When it disappears out of view signs with northerly declination are rising north of the east point of the horizon (i.e. Aries-Virgo - lie above the plane of the celestial equator).

You can switch your attention back and forth from the graphic of the celestial sphere (on the right) to the graphic of the astrological chart (on the left) to confirm this.

Once you have this fixed in your mind, switch your attention to the other side of the graphic which represents the western horizon. Now due to how Walter has set up the orientation of the globe we can't quite see the western point. But you can see that the ecliptic again moves in and out of view. As the ascendant moves out of view, the DES moves into view. You can see the planets setting on the western horizon. This depicts the fact that as signs with a northerly declination rise (Aries-Virgo), signs with a southerly declination set (Libra-Pisces), and vice versa.

Unfortunately the animation can't be slowed or stopped. Ideally it would be possible to animate this and click through a day's motion. This should be possible using Walter's software however. It's a long time since I used it so I can't quite remember the details. However, this graphic of the celestial sphere shows the phenomenon you are seeking to understand.

I hope that helps.

Hi Dima Gur -

How do you spot the MC in the animation? Is the thin white line going from south to north, the Meridian?
If yes, then the point in which that line intersects with the ecliptic (up at the top) should be the MC...

Yes - that's right. The prime meridian runs through the south point of horizon (S), the zenith (the point at which the prime meridian intersects with the prime vertical - running through the east point of the horizon and the west point of the horizon), and the north pole of the celestial equator (blue stick marker, partly obscured). The nadir would be the corresponding point opposite the zenith. The blue stick marker at the bottom of the sphere is the south pole of the celestial equator.

The MC is the point (moving up and down the prime vertical if the image is animated) where the thicker white line (ecliptic) crosses the meridian.

I have marked up an example from the useful animation app below:


The yellow line is the Sun's declination circle, the path taken by the Sun as it crosses the sky in the course of one day. In the app this can be toggled on and off using the check box on the lower right hand side of graphic.

Unfortunately the north and south poles of the ecliptic are not marked.

This the sphere set for 20 March at noon, latitude 51.8 north. This is the Vernal Equinox. See that the Sun's daily path coincides with the celestial equator (the now obscured blue line) and the Sun rises and sets due east and west respectively.



This is set for the same time of day, same latitude, but at the Autumn Equinox (22 September in this case). Again the Sun's rising and setting will align with the east and west points of the horizon.


Ed

Summer solstice, noon, same latitude:



Winter solstice, noon, same latitude:




And so on!

Which philosophically speaking, at least for a Platonist, take us back to:

"...the motions that are akin to the divine in us are the thoughts and revolutions of the universe."

Plato, Timaeus, 90.

Dima Gur wrote: Sun Mar 09, 2025 9:51 pm Tried to play with proportional houses in my solar fire. It doesn't seem to make any change, for some reason.
Also redrew the chart which was shown but no effect

Make sure you have selected a quadrant house system (Porphyry, Alcabitius, Regiomontanus, Placidus...). If you select equal or whole-sign houses, SF will continue to show the MC as a point in the zodiac.

The animation is great, thank you Phoenix.
How do you spot the MC in the animation? Is the thin white line going from south to north, the Meridian?
If yes, then the point in which that line intersects with the ecliptic (up at the top) should be the MC...

I hope Phoenix doesn't mind my answering that. The great circle intersecting the horizon at S and N is the meridian, and the great circle intersecting the horizon at E and W is the prime vertical. They intersect at the zenith, which is different from the MC. The MC is where the (rotating) ecliptic intersects the meridian.

Also, is there a simple explanation of why the Ecliptic wobbles? Its rising and setting points shifting, north and south.
Maybe some animation for that...

I see Ed answered that, but let me add this: from a geocentric perspective, it is the equator that rotates around its own axis. Unfortunately the demonstrator doesn't include the equator, but if you set 20 March as the date and select 'loop day' as the animation mode, the yellow circle (the Sun's declination circle) will be identical with the equator.

The ecliptic (the wobbling white circle) is not rotating around its own axis, but is being dragged along, as it were, with the equator. Its wobbling motion is a result of the ecliptic not being parallel to the equator, but inclined to it at an angle of some 23½ degrees.

And once again, Ed and I reply simultaneously!

One final image:

Here is the situation with precisely 6H 00M of sidereal time on the meridian. This is the time each day when 0 Aries sets exactly due west and 0 Libra rises exactly due east. The corresponding sidereal time of 18H 00M gives the opposite zodiacal configuration - 0 Aries rises due east and 0 Libra sets due west. This will occur every day at this sidereal time wherever one is and at whatever latitude one is. Of course, 6H 00M of sidereal time on the meridian places 0 Cancer zodiacally on the meridian and 0 Capricorn on the IC. At 18H 00M the reverse situation applies - 0 Capricorn is on the meridian and 0 Cancer is on the IC. This is why the cardinal degrees are so critical astrologically, they are on the angles and square to each simultaneously at these sidereal times at all latitudes.


In the image above I have marked the approximate positions of the poles of the ecliptic: NEP - north ecliptic pole; SEC - south ecliptic pole. At 6H 00M of sidereal time the poles of the ecliptic lie on the meridian. (You can check this by carefully watching Walter's animation to see when the convergence of the zodiacal divisions of the ecliptic at the SEP momentarily cross the meridian). The same phenomenon will occur at 18H 00M of sidereal time.

Here is the corresponding astrological chart drawn for the same latitude and 06H 00M of sidereal time. If you click on the chart below to open it full size and follow the line of sign glyphs down to a line of text you will see:

S.t: 06:00:00 Tropical, meaning Sidereal Time = 06H 00M.