Second Station: Another six days and it again becomes stationary, in preparation to resume
its direct, or re-direct motion.
Maximum Brilliance as Morning Star: Some fifteen days later it is reduced to a broad
crescent and is again at its brightest, now as a morning star.
Emerges from Retrograde Arc: As it advances beyond the degree of its First Station it leaves
the retrograde arc and enters territory over which it will not retrograde during this cycle.
Greatest Elongation West: Although no longer in retrograde it has not yet accelerated to the
extent that it equals the Sun's motion, hence it continues to increase behind the Sun in
elongation and elevation for some ten or twelve days to the point of greatest elevation West
just before it commences its gibbous phase.
Smallest Phase: Some seven months later, about fifteen days before the superior conjunction,
it has decreased in visible size until it appears as a small but fully illuminated disc of less than
one-third the diameter it had at its brightest phase. Then comes the next superior conjunction
and invisibility, completing one cycle from one superior conjunction to the next.
Venus's motion is entirely similar, although the intervals are longer. Where the Mercury
sidereal period is approx. 88 d. and its synodic period is 116 d. the Venus orbit of 225 days
has a synodic period of 584 days.
The cycle of the major planets is not greatly different, except that at the opposition, the Sun
and the planet arc on opposite sides of the Earth. Figure 2, a comparative illustration of the
motion of Venus as an inside planet and Mars as an outside planet, in reference to the motion
of the Earth, facilitates a ready understanding of the relationship of the orbits which produces
the phenomenon known as retrograde motion.
While the Inferior Conjunctions with a minor planet, and the oppositions to a major planet
always occur during the retrograde; the similarity ceases when gravitation is considered,
since at the opposition of the major planet the Earth is in between, hence the planet and the
Sun are exercising a gravitational pull upon the Earth from opposite sides; while at both
conjunctions of a minor planet the gravitational pull from the Sun and the planet are always in
the same direction.