Geodetic

The planetary positions are calculated as for an ordinary natal chart. However, the angles of the chart are determined solely by the location of the chart, and are not influenced by its date or time.

Using the Longitude method, the longitude of the Midheaven is determined as the longitude of the Sun minus the longitude of the chart. (East is -ve.)

Using the R.A. method, the R.A. of the Midheaven is determined as the R.A. of the Sun minus the longitude of the chart.

The ascendant and other chart angles are then derived according to the chart’s latitude.

If a user-defined geodetic offset is being used, then this offset is added to the position of the Sun (either it’s longitude or its R.A., as appropriate).

 

Johndro

This chart type is very similar in principle to the Geodetic chart type, except that a precessionary factor is added to the position of the Sun. This factor was 29°10’ of R.A. in 1930, and increases with time at the rate of precession of the equinoxes (about 46.1 seconds of arc per year). Using the longitude method, the precession in R.A. is converted to an equivalent precession in longitude before it is added to the longitude of the Sun.

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