Solar Arc

The distance the Sun travels along the ecliptic within a specified period of time. In many methods of direction and progression, the movement of the Medium Coeli is based on the movement of the Sun, which means: the distance between the Sun and the Medium Coeli always remains the same. The movement of all the other house cusps is then based on the movement of the Medium Coeli.

There is a mean and true solar arc. The former is, as the name suggests, based on average values and is based on the so-called Naibod Key which is the Sun's average diurnal movement of 59 minutes and 8.33 seconds of arc (see also: Naibodic Arc). Interpolation can be used to calculate the true solar arc , which is the actual distance travelled by the Sun on a particular day. The resulting value is only slightly different from the average solar arc.