Why do planets revolve in elliptical orbits?

In summary, the reason why planets revolve in elliptical orbits is due to Newton's law of gravitation, which states that the gravitational force between two objects is inversely proportional to the square of the distance between them. When applied to the motion of planets around a larger mass, such as the sun, this results in elliptical orbits with the sun at one focus. While there are some exceptions and other factors that can affect the shape of the orbits, the general principle remains the same.
  • #1
spideyinspace
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we know that planets revolve in elliptical orbits but Why should planets revolve in elliptical orbits?
 
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  • #2
spideyinspace said:
we know that planets revolve in elliptical orbits but Why should planets revolve in elliptical orbits?

It is a consequence of Newton's law of gravitation.
See e.g. here
 
  • #3
spideyinspace said:
we know that planets revolve in elliptical orbits but Why should planets revolve in elliptical orbits?

In Newton's theory of gravity, the gravitational force on an object moving near a more massive object is proportional to 1/r^2 where r is the distance between the objects. When one works out mathematically the path for an object which is falling freely under the influence of such a force (but doesn't have enough energy to completely escape) the general answer is an ellipse where the large mass is at one focus.

There are of course some special cases; the obvious one is that if the orbital speed is just right for the distance, the path is a circle. Another is that if the falling mass is heading straight for the other mass, the path is a straight line downwards.

In the case of the planets, the sun is so much more massive than the planets that each planet basically moves in an ellipse around the sun, but the planets also have a very slight effect on the sun (especially Jupiter) and on each other, which distort the ellipses, and there are also other effects related to relativity which cause some further very slight distortions.
 

1. What causes planets to have elliptical orbits?

The elliptical orbits of planets are caused by the gravitational pull of the sun. As the planets move in their orbit, the sun's gravitational force acts as a centripetal force, keeping the planets in their elliptical paths.

2. How do we measure the eccentricity of an elliptical orbit?

The eccentricity of an elliptical orbit is measured using the ratio of the distance between the foci (the two points at the center of the ellipse) and the length of the major axis (the longest diameter of the ellipse). The closer this ratio is to 0, the more circular the orbit is, while a ratio closer to 1 indicates a more elongated, or eccentric, orbit.

3. Do all planets in our solar system have elliptical orbits?

Yes, all planets in our solar system have elliptical orbits. However, the degree of eccentricity varies between planets. For example, Mercury has the most elliptical orbit, while Venus has the most circular orbit.

4. Can a planet's elliptical orbit change over time?

Yes, a planet's elliptical orbit can change over time. This can be due to various factors such as gravitational interactions with other planets or the effects of passing comets or asteroids. However, these changes are typically small and do not significantly alter the overall shape of the orbit.

5. How do elliptical orbits affect the length of a planet's year?

The length of a planet's year is determined by the distance between the planet and the sun, as well as the speed at which it travels in its orbit. In an elliptical orbit, a planet will move faster when it is closer to the sun and slower when it is farther away. This means that a planet's year may be longer or shorter depending on its position in its elliptical orbit. However, the overall length of a planet's year is not significantly affected by the shape of its orbit.

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