The Planetary Movements, throughout history have attracted the attention of man, with respect to the observation and subsequent studies of the celestial bodies. For this reason, theories that try to explain the movement of these bodies have emerged for many years and in other centuries. One of the scholars to make these observations was Ptolemy of Alexandria, establishing a system in which the Earth would occupy the center of the Universe.
It is interesting to note how at that time, this finding is talked about, where the observation from the earth, was the main source of information, although there was not as much technology as there is today. It is then, when the theory arises in which Ptolemy indicated that around the Earth the other celestial bodies would move describing orbits, whose shape would be an epicycloid.
At this point, what defines the epicycloid it is what the planet would describe with uniform movement a circle, epicycle, whose center moved along another circle of greater radius that is occupied in its center by the Earth. This last circle is called the deferent. In addition to this theory, there were others that were accepted as valid until the XNUMXth century, since Copernicus considered that all the planets, including the Earth, revolved around the Sun, which would be at the center of their orbits.
Today we know that the celestial movements are uniform, eternal, and circular or compounds of various cycles. On the other hand, it is clear that the center of the Solar System is the Sun. This is because stars are distant objects that remain fixed. Although from Earth they seem to move, the truth is that they are further away than we think and do not orbit around the Sun.
Earth movements
It is important to mention that it was Galileo who reinforced the Copernican theory justifying it with his experimental results. The fact that the moons of Jupiter, which are the medic planets, revolve around it implies first of all that not everything revolves around the Earth. The observations made, through the telescope, showed that the stars, in addition to not being seen to increase when using the telescope, make him deduce that they are very far from us, that is, no parallax can be observed.
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La Galileo's vehemence When it came to continuing to defend the heliocentric theory of Copernicus, it led him into serious problems, having to face a conviction by the Inquisition and an arrest in his house on the outskirts of Florence, where he only received visits from one of his students, such as Torricelli.
For this reason, before mentioning the movements of all the planets, it should be noted that individually the planet Earth has three movements, which are: the daily rotation, the annual revolution, and the annual inclination of its axis. The retrograde motion of the planets It is explained by the movement of the Earth. The distance from the Earth to the Sun is small compared to the distance to the stars.
Planetary movements and their laws
The human mind is worthy of admiration, because it is capable of understanding the behavior of nature, after a meticulous study. It was the same way of reasoning, the one that could venerate a nature that achieved in such a finished form, and with such generality, a principle as elegantly simple as the law of gravitation. It is precisely this law that states that every object in the Universe attracts every other object. To better understand the laws of planetary motion, this attraction should be considered.
The attraction between two objects, through the gravity, is carried out with a force such that for any two bodies it is proportional to the mass of each one and varies inversely with the square of the distance between them. Add to this the fact that an object responds to a force by accelerating in the direction of the force, by an amount that is inversely proportional to the mass of the object.
This information is necessary for a sufficiently talented mathematician to deduce the full consequences of these two principles. However, it is important to describe in more detail the consequences of these principles and the behavior of the planets, which are fundamental to understanding the laws of planetary motion.
These last ones were investigated by the German astronomer Johannes Kepler, who elaborated different studies on the celestial bodies located in the universal space.
For this reason Kepler was considered a man with a vast amount of revolutionary ideas during the XNUMXth century. However, there is no doubt that the greatest achievement of this great scholar of science was to formulate the rules of planetary motion.
Kepler's 3 Laws
Regarding planetary movements there are 3 laws of planetary movement. Initially, the astronomer Tycho Brahe commissioned Kepler to verify his observations on the Mars orbit. Based on data from these studies, they were of great help to Kepler, as he announced his first and second laws of planetary motion 4 years after Brahe's death, in 1605. Later, in 1619, Kepler published the third law .
Kepler's first law
This first law shows that the planets in their movement around the Sun, describe flat orbits, which are closed and with an elliptical shape in one of whose foci is the Sun. This is when you can observe the heliocentrism theory. For this reason, in this first law it was established that all the planets move around the Sun in elliptical orbits and with the Sun at one of the focal points of each ellipse.
Kepler's second law
In this second law, show the segment joining the sun and a planet that sweeps equal surfaces in equal times. This phenomenon is called the law of areas. What defines the areolar velocity as the area swept by the position vector of a planet taking the Sun as the origin. This law can announce that: "The areolar velocity of a planet is constant throughout its entire trajectory."
It is important to note that this second law states that the radius vector that join any planet with the Sun sweep equal areas in equal times.
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Kepler's third law
This is when it is indicated that the quotient between the square of the period of any planet and the cube of the semi-major axis of the ellipse described by the planet, has the same value for all of them. This indicates that this third law is the one that establishes that for any planet, the square of its sidereal period is proportional to the cube of its average distance from the Sun. It should be noted that a sidereal period is defined as the time of each complete revolution.
Although it seems to be difficult to understand, it is still a very elegant solution to calculate the positions of the planets. Perhaps the most surprising thing about Kepler's discovery is that its first two laws were stated before the first refracting telescopes used by pioneering astronomers such as Galileo Galilei were invented. Which indicates that his studies were based on direct and detailed observation, in the open sky.
Interesting facts about Kepler
Although Kepler himself could not understand why his laws were correct. When it came to light law of gravitation Isaac Newton, a complete understanding of planetary motion was achieved. Kepler's laws were only based on observations of planetary orbits, but incorporating Newton's proposed gravity into them, they proved to be applicable to any relatively light object orbiting a massive one.
On the other hand, today it is not considered a great challenge to know the positions and orbits of the planets Of the solar system. The reason is that Planetary Motions are a key factor in predicting the motions of satellites, such as Voyager and Cassini. These ships took advantage of the gravitational attraction of the planets to catapult themselves to enormous distances. Without the help of Brahe, the laws of Kepler and Newton, it would have been impossible to program their long trajectories.
