Personal Sensitive Points in the Horoscope


All astrologers are familiar with the Ascendant and Midheaven in a horoscope, and many will have come across the Vertex.

The Ascendant is the point on the Ecliptic where the Ecliptic intersects the Horizon to the East of the Meridian, while the Midheaven is the point where the Ecliptic intersects the Meridian above the horizon.  In polar latitudes, parts of the Ecliptic will never rise, while other parts of the Ecliptic will never set.  In these cases, the Midheaven can be defined as being the intersection towards the South (within the Arctic Circle) and the intersection towards the North (within the Antarctic Circle), even if the Midheaven is below the horizon - that is as high as that degree of the Ecliptic is going to get!

The Vertex is the point where the Ecliptic intersects the Prime Vertical, (a Great Circle passing directly overhead from due East to due West, and thence through the Nadir).  By definition the Vertex lies to the West of the Meridian, and may be above or below the Horizon.  The Vertex can be calculated by finding the Ascendant at your Co-Latitude, (i.e. the Ascendant at 90 degrees minus your Latitude, in the same hemisphere), at Sidereal Time 12 Hours later.

There are other so-called Personal Sensitive Points, (PSPs), which include the Co-Ascendant, (the Ascendant at your Co-Latitude, at the same longitude), the Equatorial Ascendant, (the Ascendant at the Equator at the same Longitude), and the Polar Ascendant, (the Ascendant at your Latitude at Sidereal Time 12 Hours later).

The eight PSPs are completed by throwing in the 0 degrees Aries Point and (for some reason) the Moon's Node.

If this seems rather arbitrary and complicated, let us try to simplify things.  Of the 8 PSPs, the Moon's Node is the odd one out.  While it is no doubt important, it does not fit into the same category as the other 7 PSPs which have something in common.

Why the 12 hours?

Why do we need to add 12 hours of Sidereal time to calculate the Vertex and the Polar Ascendant, (sometimes more sensibly called the Covertex).  I believe the answer may lie in that in the days before easy computation was available, Tables of Houses were generally only available for Northern Latitudes.  Calculations for Southern Latitudes were performed by calculating the House Cusps for the antipodean point in the Northern hemisphere, and switching the signs on opposite cusps.  This involved adding 12 Hours to the Sidereal Time.  It seemed more logical to me, when I started looking at the Vertex to calculate the opposite point in the East, the Antivertex, and this involved subtracting 90 degrees from a North Latitude to give the Co-Latitude in the Southern Hemisphere, at the same Longitude as the birthplace.  A similar argument holds for the Covertex and Anticovertex.

One Meridian

Calculating these PSPs in this fashion involves a simple progression down one line of Longitude, the Meridian.  Near the Poles, the Ascendant is always very close to 0 Aries or 0 Libra, since most of the Ecliptic cannot rise or set there.  At the North Pole, 0 Libra rises by convention, though arbitrarily near the Pole, the last fraction of Virgo rises, followed by the first fraction of Libra, followed by a flip to the first fraction of Aries and the last fraction of Pisces, and a flip back to Virgo.  The Aries-Pisces portion is retrograde when rising!   The Poles are therefore firmly associated with 0 Aries and 0 Libra rising.

Moving South from the North Pole, the Birth Latitude comes next, (giving rise to the Ascendant), for Latitudes greater than 45 degrees North, then the Co-Latitude, (giving rise to the Co-Ascendant).  For Birth Latitude less than 45 degree North, it is the other way round.  Next comes the Equator, and the Equatorial Ascendant, followed by the Antivertex and Anticovertex, (in either order, as above).

Another House System?

Well yes and no.  Since 6 PSPs (and their 6 opposite points) lie on one Great Circle, involving the Longitude line of birth, and the Longitude line 180 degrees away, it is possible to construct a chart with the Ecliptic projected onto this Great Circle, complete with House Cusps.  The idea is not new, but it receives very little attention.  The East Point House System uses such a projection.  The house cusps divide space into 12 equal lunes, with cusp lines all intersecting at the horizon points at due East and due West.  The chart is usually highly distorted, with houses of very unequal size, (as far as the Ecliptic is concerned).  Vertex lovers will be delighted that the Antivertex or Vertex always falls at cusp 10 in the East Point System, according to whether the Vertex or Antivertex is above the Horizon.

So the East Point system is not new, but it does lead to an idea that is new, or at least I have not come across it previously.  Since the East Point System is unfamiliar, and not for the faint-hearted, I shall demonstrate the idea for the Campanus system.

Campanus Revisited

Campanus is one of the more popular House Systems where space is divided equally.  The Prime Vertical is divided equally into 12 sections, and great Semicircles are drawn from due North to due South cutting the Prime vertical half way along their paths.  Thus the First House Cusp scuttles right along the Eastern Horizon, while the Seventh Cusp completes the circle along the whole of the Western Horizon.

It is possible to project the positions of the planets onto the Prime Vertical.  Since planets do not necessarily lie on the Ecliptic, a planet near a House Cusp may turn out to be in a different house.  A table can be calculated showing exactly how many degrees into a house a planet is placed.  All Houses are 30 degrees in length along the Prime Vertical, though this is not the case along the Ecliptic, (except in a couple of very rare instances).

A chart can then be drawn showing the planets in their correct degrees of the houses.  Aspects can even be used, (e.g. a trine from 10 degrees in the Third House to 10 degrees in the Seventh).  These will not be Ecliptic aspects, but aspects along the Prime Vertical.  So far so good.

Now comes the difficulty.  It would be nice to have signs in this Prime Vertical Chart.  After all, horoscopes are supposed to have signs and houses are they not?  So how to arrange the signs?  With 360 degrees of Prime Vertical circle there must be a way.  What most people would do is to cram the signs into the houses, with some houses being larger than others, (measured along the Ecliptic).  Is there a way of having equal Campanus Houses and equal signs?

A clue comes from looking at another system, based on the Celestial Equator.  Here astronomers use Right Ascension (RA) and Declination as their  measures.  It is quite possible to equate the first thirty degrees of RA (measured along the Equator) with Aries, the next 30 degrees with Taurus and so on.  Indeed some Ephemerides give positions in both Ecliptic Longitude and Latitude, along with RA, (using signs along the Equator) and Declination.  A planet can be, for example, in 1 degree Taurus along the Ecliptic, and in 29 degrees Aries along the Equator.  Aspects can form along the Equator, that are not present along the Ecliptic, and vice versa.

So how to proceed?  The crossing points for the Ecliptic and the Equator are at 0 Aries and Libra, so obviously a planet or point at 0 Aries (with no Latitude/Declination) will be at 0 Aries in both systems.

The points of intersection of the Prime Vertical and the Ecliptic occur at the Antivertex and the Vertex.  So a planet or point on both the Ecliptic and the Prime Vertical will have the same position in each system, or at least it would be very odd if it did not!

So, for example, if the Antivertex is in 15 Taurus, at an altitude of 20 degrees in the East, the Ascendant, (along the Prime Vertical) will be 20 degrees after 15 Taurus, or at 5 Gemini.  Cusp 10 will be at 5 Pisces.  A planet anywhere on the upper meridian will have position 5 Pisces, whatever its Ecliptic position.  A planet half way through the eleventh house will be at 20 degrees Aries in the Prime Vertical Chart.

All we have done is to perform a coordinate transformation, in line with simple rules, but there is a question as to whether the technique has any validity.  Can a Prime Vertical chart be interpreted?  If so, can we have more than one horoscope?  In my opinion the short answer is yes, provided you do not mix systems.  The Equal House System, an Ecliptic-based method of house division., responds well to transits and progressions.  The Prime Vertical chart also responds well to transits and progressions, even though these may occur years earlier or later than the Ecliptic ones in the case of the outer planets.  You do however have to remember to convert progressed or transiting Ecliptic positions to the appropriate Prime Vertical positions in the natal chart!

For what it is worth, my experience suggests that the Prime Vertical chart, where the signs are added  based on the position of the Vertex and Antivertex, adds an extra dimension to chart interpretation.  The Equal House method seems to relate more to psychological events, while the Prime Vertical chart seems to relate more to events.  Long live the Vertex!  Maybe Personal Sensitive Points can lead to personal sensitive charts :-)

The same technique can be used for some other house division methods, such as the East Point and the Zenith system, though I have not investigated these extensively.

Relevant Links

The Personal Points and how to calculate them

Personal Sensitive Points and how they might be interpreted

Swiss Ephemeris One of the best sites for astro software.


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Page created 14th April 2001

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