The retrograde motion of a celestial body is a change in its position in the sky in the opposite direction to that in which it is usually observed. These are several phenomena in terms of their mechanism, which are caused by various reasons. However, there is no need to be afraid of any of them.
The retrograde movement of the planets
On February 23, 2025, Mars will complete its retrograde motion, which has been going on since December 7, 2024. Astrologers may see this as a sign. However, in reality, no visible change in the direction of the planet’s movement in the sky has ever affected any events on Earth. To make sure of this, it is enough to know what it is and how it occurs.
To begin with, we need to clarify that the term “retrograde motion” is applied to celestial bodies in at least two different ways. When someone tells you that a planet is currently retrograde, they are always referring to its apparent retrograde motion. And then there is the true retrograde, which we will discuss later.
People noticed this phenomenon in ancient times. During the day, the Sun, Moon, and all the stars move from east to west. This phenomenon is caused by the daily rotation of the Earth. As for the planets, their very name, which means “wandering” in Greek, suggests that although they rotate daily along with the rest of the celestial bodies, their position relative to the constellations changes over weeks and months.
Their usual direction of movement is the same as during the diurnal rotation – from night to night, they “crawl” from east to west. However, at some point, they stop and start moving in the opposite direction, i.e., from west to east. This phenomenon is called the apparent retrograde motion of the planet. It lasts for some time, after which it stops again and returns to normal behavior.
The visible retrograde movement
At first glance, the retrograde motion of the planets may seem like something outlandish. After all, of all the objects that are visible in the night sky with the naked eye, they are the only ones that behave in this way. However, there is a fairly simple scientific explanation for this.
The retrograde motion is determined by the movement of the Earth itself in its orbit. When a planet, for example, Mars, is just coming out from behind the Sun, its motion is straight. For several months, our planet catches up with it. However, as the confrontation approaches, i.e. the point where the Earth is between the planet and the Sun, the planet’s motion in the sky slows down and at some point reverses.
This happens because we are overtaking it. Imagine that you are driving down the road in a car. In the distance, you can see cities and forests. And ahead of you is a car that you are quickly overtaking. At first, it seems that it is moving towards you very slowly. But then the speed increases, and at the moment of overtaking, it rushes towards you at breakneck speed. And the movement of forests and houses on the horizon remains constant.
With the retrograde motion of the planets, it’s the same. Every day, the position of the stars in the sky changes by a certain almost constant amount due to the Earth’s orbital motion. The same thing happens with the outer planets, but here, this value strongly depends on the distance to the Earth.
Usually, the planet’s speed is faster than that of the stars, so it appears to be ahead of the stars in its motion. However, as the planet approaches the confrontation, at some point, the distance by which it moves in the sky becomes less than that of the stars. To an observer on Earth, it seems that the planet is “going backward” relative to the constellations, and this is what we perceive as retrograde motion.
With the inner planets, the situation is similar, with the only difference being that their retrograde motion is observed not so much relative to the stars as to the Sun itself. And the retrograde motion is not tied to the opposition, but to the moment when Mercury or Venus are between us and the Sun, so it is at this moment that we do not see them.
But the retrograde movement begins a few weeks before, gradually picks up speed, and then slows down and stops altogether. so you can still see its initial and final stages. And astrologers, at this point, say that you have to be careful.
Mercury retrograde movement
The speed of the planet’s retrograde movement increases until the moment of confrontation and then begins to decrease until the planet stops in the sky and begins to move in its normal direction.
It is important to note that all this time, the speed of Jupiter or Saturn’s orbit, i.e. the number of kilometers they travel in space per second, remains virtually unchanged. Only the angular distance they travel on the Earth’s sky changes.
It is also worth noting that the farther a planet is from the Earth, the longer its retrograde motion is, both in days and as a fraction of the time interval between two moments when the planet is hidden from us behind the Sun (synodic year). For Mars, these values are 73 days and 9%, while for Neptune they are 158 days and 43%.
It is also worth noting that retrograde motion, in addition to planets, is performed by all other objects moving around the sun in the ecliptic plane, such as Ceres, main-belt asteroids, Pluto, and other dwarf planets on the outskirts of the Solar System.
Another definition of retrograde motion
And everything would be fine if astronomy didn’t have another definition of retrograde motion, which is practically unrelated to the first one but can be misleading. This is the case when another body orbits around one, and the direction of the second body’s orbit is opposite to the direction of the first body’s orbit.
For example, under this definition, the motion of all eight major planets of the Solar System relative to the direction of rotation of the Sun is always straight. For six of them, it is also straight when considered relative to their rotation. In this case, only Venus and Uranus are retrograde, and their motion is always so.
The Moon’s motion around the Earth is straight. The same goes for most of the large satellites. The exception is Triton, Neptune’s largest moon. It is suspected that it was captured by the gravity of the icy giant.
But among the small satellites, the number of retrograde satellites is quite large, although smaller compared to those that have the same direction of rotation as the planet. The rings of gas giants consist of a huge number of small bodies. Their rotation is also mostly straight.
The exception is one of Saturn’s rings, where the particles have a retrograde direction of motion. The thing is that it was formed thanks to the moon Phoebe, whose rotation direction is opposite to that of the gas giant.
And yet, there is one object whose motion changes from direct to retrograde when it comes to its position in the earthly sky. Strangely enough, it is the Sun. The fact is that the center of rotation of the Solar System does not coincide with the center of the star in its center. Its position is determined by the joint action of the gravity of all the bodies that make up the system.
So, sometimes, our star also moves around this point. However, depending on which way the planets are pulling it, this movement is either direct or retrograde.
The retrograde motion also exists outside the Solar System. Most discovered exoplanets rotate in a forward direction, but some do so in the opposite direction to that of their star. And the stars themselves can be such if we talk about their rotation around the center of the Galaxy. The majority of them do rotate in a straight line, but some, especially if they are not in a disk but in a halo, are indeed retrograde.
In general, it should be remembered that regardless of the definition, retrograde movement can only be defined about something. That is, it does not differ from the forward movement in any way. And it certainly doesn’t affect anything in your life.
