Retrograde motion of a superior planet occurs when the earth catches up to and passes the superior planet. suppose a superior planet completes its orbit in exactly 18 months (sidereal period). how many months will elapse between a time when the earth passes this planet and the next time it does so?

36 months

Explanation:

The earth complete its orbit in 12 months

While the superior planet complete its orbit in 18 months

Therefore since they are moving in the same direction, both planet will meet at the point where the superior planet and earth completes x and x+1 number of orbits.

Where x is a constant that represents number of orbits.

The period y when they both complete x and x+1 orbit respectively are;

y= 18x and y = 12(x+1)

Equating the two equations, we have,

18x=12(x+1) = 12x + 12

18x-12x= 12

x= 12/6= 2

Since x= 2

y= 18x=18×2= 36months

y= 36 months

Goodluck...

36 month

Explanation:

The retrogradation is just a natural astronomical phenomenon quite common in our solar system, nothing magical to which to attribute special powers or anything similar. I will try to explain it in the simplest way possible with the support of the selected image, and then I will explain the symbolic meaning or the possible effects caused by its particular influence. In simple terms, the retrograde movement of a planet is an apparent backward displacement of its orbit for a certain period of time, but only seen from Earth, since it is not a real phenomenon, but a visual movement, or said of another form, is the optical illusion that occurs when the orbit of the Earth reaches and advances the orbit of another planet. As shown in the image, from the perspective of the Earth (celestial point) the advance of the planet Mars (red point), at a certain moment of its orbit, is in front of the Earth, however, then comes a point when the Earth reaches and matches the orbit of Mars, which seen from Earth,.

it is observed as if that planet began to recede, although in reality, it is the Earth that is reaching it. In the end, you reach another point where the advance of Mars again reaches Earth and that is seen, from Earth, as if Mars had regained its direction forward. This event occurs every two years, in the case of Mars, but each planet has its own retrograde cycle depending on its orbit. And this would be the practical or astronomical explanation of the phenomenon known as the "retrograde movement" of a planet, that simple.

The ironing time of a planet, which is the time it takes for that planet to travel an orbit, that is, to go around the Sun.

We will need another concept called SYNODIC TIME, which is the time elapsed between 2 consecutive alignments of 2 planets with the Sun, that is, the time that elapses since two planets align with the Sun, until they align again.

For outer planets, such as Jupiter, the procedure is the same, but changing N + 1 to N-1

S = synodic time / number of orbits = N Earth years / N-1 orbits, that is, the time Jupiter needs to complete a full circle around the Sun is N / N-1 Earth years.