Elliptic orbit of earth round the sun

In summary, circular orbits are impossible to achieve in practice due to various factors such as the presence of other celestial bodies, the shape and mass loss of the Sun, and the limitations of Newtonian gravity. While theoretically possible, achieving a perfectly circular orbit would require precise orbital speed and direction, making it highly unlikely in reality.
  • #1
Apache
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Hello, I would like to ask why if the Earth rotate around the Sun in circle orbit, it must have an kinetic energy equal to negative half of potential energy it has at anytime rotating round the sun, which Ek = -Ep/2 ! If this situation cannot be achieved, our Earth will move in a new ellipse orbit round the Sun. I read this article from a Chinese website, just troubling why Ek = -Ep/2 for circle orbit to be formed. Hope can get perfect answer...
 
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  • #2
First things first: The Earth does not orbit the sun in a perfectly circular orbit. In reality, nothing does: There is no such thing as a perfectly circular orbit. They are impossible to achieve in practice.

I'll ignore:
  • The presence of the Moon, other planets, other stars;
  • That the Sun and Earth are not perfectly spherical;
  • That the Sun is losing mass because it is radiating light and spewing particles in the form of the solar wind;
  • That nature does not obey Newton's law of gravity (general relativity is closer to the truth).
Each of the above makes a perfectly circular orbit not only a practical impossibility but also a theoretical impossibility. Ignoring those details, assuming the Sun and Earth are point masses, and assuming Newtonian gravity rules the universe, then circular orbits are a theoretical possibility.

However, they are still impossible to achieve in practice. For a given orbital distance between the (point mass) Sun and a (point mass) planet, there is one and only one orbital speed that yields a perfectly circular orbit, and then only if the velocity is perpendicular to the radius vector. If the velocity vector exhibits any deviation whatsoever from orthogonality or any deviation whatsoever in magnitude from the circular velocity then the planet will not be in a circular orbit. It will be in an elliptical orbit (or a parabolic orbit, or a hyperbolic orbit) instead.
 

1. What is an elliptic orbit?

An elliptic orbit refers to the path that a celestial object takes as it revolves around another object in an elliptical shape. In the case of the Earth, it is the path it takes around the sun.

2. Why does the Earth have an elliptic orbit around the sun?

The Earth's elliptic orbit is a result of the gravitational pull between the Earth and the sun. This pull causes the Earth to revolve around the sun in an elliptical shape rather than a perfect circle.

3. How long does it take for the Earth to complete one orbit around the sun?

The Earth takes approximately 365.24 days, or one year, to complete one orbit around the sun. This is known as its orbital period.

4. What causes the Earth's elliptic orbit to remain stable?

The Earth's elliptic orbit remains stable due to the balance between the gravitational pull from the sun and the Earth's own velocity. This allows the Earth to maintain a relatively constant distance from the sun throughout its orbit.

5. Does the Earth's elliptic orbit affect its seasons?

Yes, the Earth's elliptic orbit does affect its seasons. The tilt of the Earth's axis as it revolves around the sun causes the varying lengths of daylight and temperature changes that we experience as seasons.

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