Astronomy for Astrologers III
ASTRONOMY FOR ASTROLOGERS III
RETROGRADE MOTION OF THE PLANETS
All planets revolve around the Sun from west to east, which is termed their direct motion. Due, however, to the Earth's own orbital motion in the same direction, the other planets at certain times appear to the observer on the Earth to gradually slow down until they "stop" or "stand still", before moving in the reverse (clockwise) direction to normal.
When a planet moves in this reverse direction along the ecliptic it is said to be retrograde. This is indicated in the ephemeris by the capital letter "R" against its its longitudinal position. When a planet appears to be motionless, before turning retrograde, or before changing from retrograde to direct motion again, it is at its stationary points or stations and is then said to be stationary.
The Sun, being the axis for the Earth's orbital motion, can never appear retrograde. Neither can the Moon.
When a planet is retrograde in relationship to us, it has great astrological significance because it alters the influence of the Planet upon us in a necative way.
e.g. When Mercury is retrograde, it generally is a time poor for mental activity and obstructing and delaying in all realms of communication.
In the illustration, retrograde motion is shown in 2 diagrams. The top diagram shows the apparent "loop" performed by a superior planet (planets further away from the Sun than the Earth) in the process of reaching two stationary points which enclose between them the arc of retrogression (or retrogradation).
Between the arc ABC the planet appears to move eastwards (direct) with reference to the stars or zodiac, its angular motion decreasing as it approaches C (stationary point). Along the arc CDE the planet appears to move westwards (retrograde) until E (stationary point) is reached. The arc EFG traces its eastward and direct motion again. As can be deduced from the positions of
Sun, Earth, and superior planet in the lower diagram, retrograde occurs only around the time of opposition for a superior planet.
With Venus the period of retrogression always occurs
about 3 weeks before inferior conjunction and extends
for 6 weeks, direct motion beginning again about
3 weeks after inferior conjunction. Venus therefore
has to be between the Sun and Earth for their angular
relationship to produce apparent retrograde motion. In
a synodic period (successive superior conjunctions with
the Sun) of 584 days, Venus is retrograde for an average
of only 42 days, as against direct motion for
542 successive days.
Mercury, like Venus, can only be retrograde when nearest to the Earth, between the Earth and the Sun. Midway between Greatest Elongation East and inferior conjunction Mercury appears to be stationary because (as with Venus similarly placed) for a short time it is travelling exactly towards the Earth. An inferior planet is, therefore, always retrograde at inferior conjunction. Mercury's period of retrogression averages 20-24 days, when the planet again appears stationary, midway between inferior conjunction and Greatest Elongation West, due to its then travelling exactly away from the Earth. In a synodic period of 116 days Mercury retrogrades for an average of 22 days, and moves direct for 94 days. Mercury is retrograde for about 20 per cent of its synodic period, Venus for only 7 per cent. The illustration can be used to illustrate the retrograde motions of Mercury and Venus if we think of the orbit shown for the superior planet as the orbit of the Earth and the orbit that is indicated as the Earth's as
that of either of the two inferior planets. In this sense we see that, viewed from the superior planet towards the inferior planet, retrogression does actually occur between midway point Greatest Elongation East inferior conjunction and inferior conjunction - Greatest Elongation West (B and F representing maximum elongation). Similarly, as viewed from Mars, the Earth would always appear retrograde around its inferior conjunction with the Sun.
Astronomy for Astrologers IV
"Those who deny the influence of the planets violate clear evidence which for educated people of sane judgement, it is not suitable to contradict."
- Tycho Brahe (1546-1601), 'De Disciplinus Mathematicis'.