Apply Geocentric Correction to Latitude

It is possible to calculate charts based either on geographic (also known as geodetic) latitude or geocentric latitude.

Atlases such as the ACS International Atlas and the ACS American Atlas contain geographic latitudes. Geographic latitudes are based on the measurement of the angle of the local horizon (also known as the geodetic horizon) onto the celestial sphere. It is assumed that all latitudes entered into Solar Fire are geographic latitudes, and all displayed latitudes, such as in chart details text, are geographic latitudes.

However, because the earth is not perfectly spherical it is also possible to define a latitude based on where the horizon would be if the earth was a perfect sphere, which also corresponds to the angle of a line from that location to the center of the earth. This is known as a geocentric latitude. The geocentric latitude is never more than 12 minutes of a degree different from the geographic latitude.

There are arguments for and against using each of these types of latitude. Astrologers are divided about which is the most appropriate to use.

Solar Fire always displays latitudes as a geographic latitudes. However, when this option is on, any chart calculations performed will have a correction applied to the latitude to convert it from geographic to geocentric. Any chart that has had this correction applied will have a “G” appended to its latitude. For example, a geographic latitude of 34°S55’ is displayed as 34°S55’G when this option is on.

In order to determine exactly what the geocentric correction is, you must view a “Chart Analysis” report for the chart. If the geocentric correction has been applied, then this will be specified in the report, and the corrected geocentric latitude will be shown as well as the originally entered geographic latitude.

In the "Preferences" dialog, "Calculations" tab you can specify whether to apply geocentric correction or not.

Any charts opened or calculated, or dynamic reports generated are calculated according to the current setting of this option.