Planets rotate around the sun because of the gravitational force exerted by the sun, which keeps the planets in orbit around it. This movement follows the laws of universal gravitation stated by Isaac Newton.
The Sun, with its enormous mass, curves the space around it and creates a force known as gravity. The more massive an object is, the more it attracts things around it. Just like a heavy ball placed on a stretchy sheet creates a bump, the Sun does the same with space. As a result, the Earth and other planets are constantly falling towards the Sun, but since they are also moving very quickly along their paths, they never stop "missing" their fall: this is what it means to orbit. Without solar gravity, no planet would stay aligned, and the solar system would be a joyous chaos. It is this gravitational attraction that keeps all the planets on regular and well-organized trajectories, forming the cosmic ballet we observe every day.
Initially, the Solar System was just a vast cloud of dust and gas floating quietly in space. But a disturbance—like the breath of a distant supernova—was enough to make it collapse in on itself. As it contracted, this enormous mass began to spin faster and faster, somewhat like a figure skater who accelerates their spin by pulling their arms in against their body. This initial rotational movement created a large disk spinning around the young Sun, in which the planets gradually formed. These planets, naturally inheriting the circular motion of the initial disk, continue to revolve around our star today.
Angular momentum is a physical quantity related to the rotation of objects. The faster an object rotates around an axis, or the more massive and distant it is from that axis, the greater its angular momentum. It's similar to a skater spinning: to rotate faster, they pull their arms closer to their body, thereby reducing their radius, which increases their rotation speed to conserve their angular momentum.
In the case of planets, this principle is essential: during the formation of the solar system, they inherited a certain amount of motion, which compels them today to continue orbiting the sun. Without this initial angular momentum, they would fall directly toward their star due to its powerful gravity. But this rotational motion gives them a sort of dynamic balance, preventing this fall and allowing them to remain peacefully (or almost!) on their orbit.
The orbits of planets sometimes undergo perturbations due to the gravitational influence of other celestial bodies, such as neighboring giant planets (Jupiter, Saturn). These small nudges can slightly modify their trajectories without completely disturbing them. However, the solar system, generally stable for billions of years, enjoys a dynamic equilibrium: these slight perturbations eventually smooth out over time. Exceptional external effects can still disrupt this balance, such as the close passage of a star, but this is extremely rare and takes millions of years to have noticeable consequences.
Even though the space around the Sun seems empty, it still contains a few free atoms, but in such low quantities that they generate almost no resistance to the movement of the planets. This near-vacuum of space allows the orbits of the planets to remain stable for a very long time, as they lose almost no energy. Without this nearly nonexistent friction, a planet like Earth can traverse its orbit year after year, keeping almost intact its initial momentum for billions of years. In other words, after the initial boost received during their formation, planets practically need no additional energy to maintain their orbital motion.
The planet Neptune takes about 165 Earth years to complete one full orbit around the Sun. Since its discovery in 1846, it has therefore completed just a little over one full orbit!
The Sun accounts for about 99.8% of the total mass of the Solar System, which explains why its gravitational pull dominates so strongly over the planets.
The universal law of gravitation was formulated by Isaac Newton, reportedly inspired by the fall of an apple. This "legendary" apple is said to have indirectly led to the understanding of planetary orbits!
The orbits of the planets are not perfectly circular, but elliptical. This means that each planet is slightly closer to or farther from the Sun depending on the point in its orbit.
The angular momentum, also known as the moment of inertia, is a physical quantity associated with the rotational motion of an object. It explains why planets continue to revolve around the Sun without gradually moving closer until they crash into it. In the absence of significant external disturbances, angular momentum remains constant over time, thereby ensuring the stability of planetary orbits.
No, each planet has a different orbital period. The time it takes for them to complete a full orbit around the Sun mainly depends on their distance from the Sun and their orbital speed. Mercury, for example, completes an orbit in just about 88 Earth days, while Neptune takes about 165 Earth years.
Sure! Here’s the translation: "Yes, just like the planets, many other objects orbit around the Sun, including asteroids primarily located in the asteroid belt between Mars and Jupiter, and comets that often come from more distant regions such as the Kuiper Belt or the Oort Cloud. Their orbits are often more elliptical and less regular than those of the planets."
Planetary orbits are elliptical due to the laws of gravitation described by Johannes Kepler. This is the natural consequence of the balance between the initial speed of the planets and the gravitational attraction exerted by the Sun, according to the physical laws discovered by Isaac Newton.
No, planets encounter almost no resistance in space, as it is nearly empty, apart from a few rare particles. Thus, in the absence of any significant external force, their orbital speed remains relatively stable over extremely long periods, spanning billions of years.
If the Sun were to suddenly disappear, its gravity would no longer affect the planets, which would immediately cease their orbital rotation and continue on a straight trajectory through space at their current velocity. Of course, life would be impossible, as the Earth would quickly lose its heat and light.
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