holed.
Planetary Periods, or Cycles.
The mean symbolical periods of the various bodies are the length of time between two
successive conjunctions of that body with the Sun at the same geocentric longitude, i.e,
falling on the same day of a year. In other words the Sun in its apparent annual revolution
forms conjunctions with each of the other bodies as viewed from the Earth, each successive
annual conjunction with the same body taking place at an advanced point in the Zodiac. After
a time these conjunctions themselves form a cycle of conjunctions, beginning on
approximately the same degree of the Zodiac, or days of the year. The length of this cycle
with reference to a particular planet constitutes the planetary periods. These are:
Moon: 19 years, the Cycle of Meton (q.v.).
Mercury: 79 years, with an inconstant mean advance of 1°37' each cycle.
Venus: 8 years, with an inconstant mean advance of 1°32' each cycle.
Mars: 79 years, with an inconstant mean advance of 1°34' each cycle.
Jupiter: 83 years exact.
Saturn: 59 years, with a mean advance of 1°53'
Uranus: 84 years, with a mean advance of 40'
Neptune: 164 years, 280 days; a mean annual motion of 2°10'54"
Pluto. 247.7 years, with a mean annual motion that, because of the extreme ellipticity of its
orbit, varies from 1° in Pisces through Gemini, to 2.5° in Virgo through Sagittarius.
Ptolemy cites these time-measures as follows: Moon 4y, Mercury 10y, Venus 8y, Sun 19y,
Mars 15y, Jupiter 12y, Saturn 30y. Those moderns who use his system add Uranus 90y,
Neptune 18oy, Pluto 360y. Lilley alters this, as regards the Moon to 25y, and Mercury to 20y;
others assign 27y to Mercury.
By means of these periods one is able to arrive at a rough approximation of a planet's position
at a given date in a year for which an ephemeris is unavailable; as follows: