## The three great celestial circles: the ecliptic, the local horizon and the local meridian.

Earlier, we spoke of ecliptic-based house systems (c.f. blog 24 January 2021).

In the course of talking about these older house systems, we are going to look at the ecliptic, the horizon and the meridian, see what they look like in the sky above us, and finally we will look at how they are represented in an astrological chart.

The easiest house systems to calculate are the ones that are based on the ecliptic. The three major house systems based primarily on the ecliptic are: (1) the whole sign house system (WSH), (2) the equal house system, and the (3) Porphyry house system.

These three house systems use as their basis three great celestial circles: the ecliptic, the local horizon, and the local meridian and are easy to calculate.  All one needs to know is the longitudinal position on the ecliptic of where the ecliptic meets the horizon, this is called the ascendant.

Then we need to find the point where the ecliptic meets the local meridian, this is called the midheaven.

Once we know these positions, the rest of the calculations can be done in one’s head!

I’d like to introduce a more complex house system, but before we get to that, let’s review the basic celestial circles that we have covered so far: the ecliptic, the horizon and the meridian.

The Ecliptic:

The ecliptic, of course, is the apparent path of the Sun as it is seen from the point of view by an observer on earth.

The five visible planets never drift too far from the path of the ecliptic, so in astrology we usually measure the longitudinal position of the luminaries and planets, including the outer ones, as longitudinal degrees along the 360° circle of the ecliptic, which by convention we divide into twelve sectors of 30° of longitudinal position each.  Each of these twelve sectors is represented by an astrological constellation (Aries, Taurus, Gemini, etc.), which may or may not correspond with the ones in the sky.

The Horizon:

The horizon is the great circle on the celestial sphere that is directly between the zenith (the point directly above you) and the nadir (the point directly below you).

The horizon is always perpendicular to the local zenith and nadir, that is to say the horizon is 90° from the ascendant.

The Meridian:

The meridian is the great circle passing through the celestial poles, as well as the zenith and nadir of an observer’s location. In astrology, the midheaven is defined as the point where the ecliptic meets the local meridian.

How the great circles are represented in an astrological chart:

In an astrological chart, we squish these great celestial circles together, we flatten them so that they are represented by straight lines:

The outer circle represents the ecliptic, and on it we see the degrees of the house cusps, which were calculated in Porphyry in this chart.

The vertical line going from left to right, from 5° Leo to 5° Aquarius, represents the horizon, which of course is actually a circle, not a straight line.  Because western astrology was developed in the northern hemisphere, the Sun was always to the south.  So since the chart assumes that we are facing south, the east is on the left and the west is on the right.  This convention has stayed with us through the ages, and we use it today, even if we live in the southern hemisphere.

Finally, the vertical line that goes from the bottom at 15° Libra to the top at A5° Aries represents the local meridian, which of course is also a great circle, and not a straight line (c.f. illustration 3).  The point of the midheaven represents the point where the two circles intersect: it is the point of intersection of the meridian with the ecliptic.

The beginning of the tenth house in a quadrant house system such as Porphyry, Alcabitius, Campanus, Regiomontanus or Placidus is called the Medium Coeli (M.C.), which is Latin for midheaven.

The M.C. is where the Sun reaches its highest point in the local sky, NOT to be confused with the zenith, which is the point directly above the observer.

So, to give an example, if one is in the northern hemisphere at a mid-latitude location, for example Wisconsin, or in Europe in France, the Sun would be towards the south as it rises, culminates, and sets.  The Sun only passes directly overhead the observer at the equator.  The Sun travels along the ecliptic, the local meridian is perpendicular to our local horizon, so basic physics tells us that the Sun will reach its highest point when, travelling along its path on the ecliptic, it meets our local meridian.

Our local zenith is also on our local meridian, it is directly above where one is standing.  But the local zenith is not on the path of the ecliptic, unless we happen to be standing exactly on the equator!

Having reviewed these three basic circles, in the next blog I hope to cover later astrological house systems.  The next one we will cover is the Placidus house system.

—ooOoo—