# Why is earth's path is elliptical?

1. Oct 11, 2007

### kamalee

Why is earth's path is elliptical?why not circular?

2. Oct 11, 2007

### Garth

Welcome to these Forums kamalee!

Why should it be circular?

A circular orbit is a special case of the general elliptical orbit in which the eccentricity is exactly zero.

As nothing is exact in the real world the Earth's orbital eccentricity is near zero but not exactly zero.

In fact e = 0.016722, therefore its orbit is elliptical, just as Kepler's laws says it should be....

Garth

Last edited: Oct 11, 2007
3. Oct 12, 2007

### BosonJaw

Do any truly circular orbits exist (Eccentricity = 0)?

4. Oct 12, 2007

### mathman

None of the planets have 0 eccentricity. I suspect most of the artificial earth satellites have a very small eccentricity, so it is possible one or more might be zero. However it would be hard to maintain since the moon would exert some perturbing force.

5. Oct 12, 2007

### Staff: Mentor

Well, the answer can be seen in probability: Since, as Garth said, 0 is just one possible eccentricity, the odds of that happening are infinitessimaly small. So no, it would really be impossible to have an exactly zero eccentricity.

6. Oct 12, 2007

### BosonJaw

Thanks Guys!!!!

7. Oct 28, 2009

### Visualedtech

There is a simple explanation. The sun is in motion. It is not static in the universe.
The Earth revolves around a moving object. Hence an elliptical orbit.
No Math required on this one.

8. Oct 29, 2009

### ideasrule

As someone mentioned in the other thread, that's incorrect. The Sun doesn't care whether it's in motion or not; there's no way to tell anyhow because there is no privileged reference frame.

When talking about the shapes of orbits, it's usually done from the reference frame of the barycenter. Obviously, an orbit's shape is going to be different if you watch it from, say, the reference frame of a cosmic ray.

9. Oct 29, 2009

### DaveC426913

Visualedtech, stick to what you know. Your knowledge of orbital mechanics is ... limited.

Also, this post is two years old.