The Midheaven is not always the most ‘elevated point’ of the ecliptic. That role is covered by what we refer to as the ‘Nonagesimal’. In this video made with Stellarium I have indicated the moving point with arrows, the white circle is the Celestial Equator, and the red one is the Ecliptic.
The Midheaven is the ever-changing point of intersection between the Ecliptic and the local Meridian. It varies in altitude, but always points towards the Depressed Pole (heteronymous to the observer’s Latitude). At extreme Latitudes this intersection can even occur under the Horizon, giving rise to one of the well-known polar area anomalies which challenge quadrant-based House systems.
The Nonagesimal is the ‘most elevated’ point of the ecliptic at any given time during the diurnal rotation of Earth. This point oscillates in altitude, but it moves Eastward and Westward. The more extreme the Latitude of the observer, the wider such oscillation in terms of Local Hour Angle (Equatorial coordinates), Celestial Longitude (Ecliptic coordinates), or Azimuth (Local coordinates). When one of the Solstitial Colures aligns with the Local Meridian (0 Cancer or Capricorn culminate), two major alignments happen: the Asc. and Desc. are equidistant from the cardinal points North and South, and the Midheaven coincides with the Nonagesimal.
The Nonagesimal derives its name from ‘ninety degrees’, therefore it indicates a point which lies 90 degrees away from the Ascendant (and Descendant). According to spherical trigonometry, two intersecting great circles reach maximum separation on a plane which is orthogonal to the axis of their intersection. Many will have realized that if they use the Equal House system, they consider the Nonagesimal as the 10th cusp. The 4th is opposite and under the Horizon. Even with quadrant systems, it is so important to consider the hard aspects which planets form to the Ascendant/Descendant axis! So there is something quite profound in this particular point. The range of Nonagesimal oscillation depends on the Latitude: in fact, at high Latitudes the Ascendant can separate wildly from the East/West axis (when the Solstitial Colures rise/set).
Astrology’s wonder is that it can bring together the Soul and astral mechanics.
Video made with software Stellarium 0.20.1, Azimuthal Equidistant Projection, atmospheric effect omitted for clarity.
