Checking the angle before interpreting it
A forward arc and a shortest angular separation use the same positions to answer different questions.
Understand the idea
The forward Sun–Moon arc follows the zodiac from the Sun to the Moon and lies from zero up to, but not including, 360 degrees. It selects Babylon’s primary collective station in ten bands of 36 degrees. The shortest angular separation takes the smaller of that arc and its complement to 360 degrees; it lies from zero to 180 degrees and is used when assessing aspects. Replacing the forward arc with the shortest angle can select a different station. Keep the full input precision through the calculation, then round only for display. A calculation checks the arithmetic of supplied positions, not their accuracy or their interpretation.
An example to work with
With a hypothetical Sun at 10° and Moon at 350°, the forward arc is 340°. That selects Station 10: floor(340 / 36) + 1 = 10. The shortest separation is 20°. Using 20° as the station input would incorrectly select Station 1. These are invented longitudes for practice.
Try the reading practice checker ↗
Which question needs the directed arc, and which needs the smaller angle?
Part of Babylon’s authored teaching framework. Symbolic correspondences offer a language for reflection and learning.