The void-of-course Moon
The concept is ancient; the modern working definition and its ephemerides date to the 1970s
A Moon 'void of course' completes no more aspects before it changes sign — a moment traditionally held to be barren for new starts. The ancient and modern definitions differ: Antiochus and Bonatti frame it for the Moon specifically, while Abu Ma'shar and Lilly phrase the rule for any planet. The modern popular definition, and the wallet-sized void-of-course ephemeris that spread it, came from Al H. Morrison in the 1970s; the figures entered the widely-used American Ephemeris when Neil F. Michelsen computed them for it in 1977.
What it measures
The stretch of the Moon's path, near the end of a sign, during which it perfects no further Ptolemaic aspect to a classical planet before its next ingress.
Where practitioners disagree
- Which definition?
Ptolemaic aspects to Sun–Saturn before ingress (modern, ours) — or Lilly's benefic-sign exception — or a fixed 30° span
Antiochus and Bonatti apply it to the Moon; Abu Ma'shar and Lilly generalise it to any planet.
This engine: No remaining Ptolemaic perfection to Sun–Saturn before the next ingress.
Sources
- William Lilly, Christian Astrology (1647)
- Al H. Morrison, Void-of-Course ephemeris (1970s)