Earth's orbit not perfect ellipse

In summary: Moon and Mars, and the gravitational field of the Earth.So which of the three arguments is more valid to you?The argument using general relativity is more valid because it takes into account the curvature of space time.
  • #1
Delta2
Insights Author
Gold Member
6,002
2,627
TL;DR Summary
Earth's orbit not perfect ellipse from the classical, relativistic, and quantum mechanical point of view
Listen to the following arguments:
  • Earth's orbit isn't perfect ellipse because classically there is the gravitational field of moon and possibly of Mars and Venus which affect it
  • According to general relativity isn't perfect ellipse because there is the curvature of space time which doesn't work exactly classically like Newtonian gravity and there are also gravitational waves which may affect its orbit
  • According to quantum mechanics, Earth is a big set of quantum mechanical particles which don't have definite orbits, therefore Earth doesn't have a definite elliptic orbit
So which of the three arguments is more valid to you?
 
Astronomy news on Phys.org
  • #2
Delta2 said:
Listen to the following arguments:
Do you have a sound file available so that I can LISTEN to them?
 
  • Haha
  • Like
Likes swampwiz, Vanadium 50, berkeman and 1 other person
  • #3
They are all valid. The way you listed them, they're just sorted in the order of increasing negligibility.
 
  • Like
  • Love
Likes vanhees71, Dale, russ_watters and 2 others
  • #4
Bandersnatch said:
They are all valid. The way you listed them, they're just sorted in the order of increasing negligibility.
Yes I also think exactly that. First argument is the most important and practical I think while the other two are mostly theoretical.
 
  • #5
Delta2 said:
According to quantum mechanics, my brain is a huge set of quantum mechanical particles which don't have definite orbits, therefore my brain doesn't have a definitive answer
 
  • Love
Likes Delta2
  • #6
Delta2 said:
First argument is the most important and practical I think while the other two are mostly theoretical.
IIRC the anomalous precession of the Earth's orbit is detectable with modern observations.
 
  • Informative
  • Like
Likes PeroK and Delta2
  • #7
Sorry what do you mean by anomalous precession? I guess something to do with the general relativity?
 
  • #8
Ibix said:
IIRC the anomalous precession of the Earth's orbit is detectable with modern observations.
I believe we have detected it now for all the inner planets (out to Mars).

Delta2 said:
what do you mean by anomalous precession? I guess something to do with the general relativity?
Yes, it's the extra precession predicted by GR over and above what Newtonian physics would predict due to the effects of all the other planets.
 
  • Like
Likes Ibix and Delta2
  • #9
Delta2 said:
Sorry what do you mean by anomalous precession? I guess something to do with the general relativity?
Yes. One of the earliest successes of GR was explaining a 43 seconds of arc per century drift in the location of the perihelion of Mercury's orbit compared to a Newtonian model. The figure for Earth's perihelion shift is much smaller but now detectable.
 
  • Like
Likes Delta2
  • #10
PeterDonis said:
I believe we have detected it now for all the inner planets (out to Mars).

Saturn too iirc
 
  • Like
Likes Delta2
  • #11
Delta2 said:
So which of the three arguments is more valid to you?
As a multiple choice question, I would have to answer D.
 
  • Haha
Likes Delta2
  • #12
The argument about the Moon (as opposed to other planets) is a little suspect. If you consider the Earth and Moon as one object, you might have no objection to the ellipse.
The argument using quantum theory is so negligible that there is not enough space in an entire book to put all the zeros after the decimal point to quantify it. That can not be defended seriously.

That being said, the first two (even including the Moon) are probably measurable deviations from an ellipse using today's technology. The third one is not.
 
Last edited:
  • Informative
Likes Delta2
  • #13
FactChecker said:
If you consider the Earth and Moon as one object
You mean their CoM does perfect ellipse around the Sun. OK but no in my mind I couldn't see them as a single object, Earth rotates around their CoM so Earth doesn't do perfect ellipse.
 
  • #14
Delta2 said:
You mean their CoM does perfect ellipse around the Sun.
Not quite. There are still effects from the other planets, and there is still the extra precession from GR. But the CoM's orbit is closer to a perfect ellipse than the path of the Earth or the Moon.
 
  • Informative
Likes Delta2
  • #15
@PeterDonis, @Ibix, in the moon-earth CoM frame, Earth (and moon) do a circle orbit or an ellipse?
 
  • #16
Delta2 said:
@PeterDonis, @Ibix, in the moon-earth CoM frame, Earth (and moon) do a circle orbit or an ellipse?
Ellipse. Both of them are in elliptical orbits about the CoM. The CoM is actually inside the Earth (since the Earth is 81 times as massive as the Moon but the Earth-Moon distance is only 60 times the Earth's radius), so the Earth's "orbit" about the CoM is actually more like a wobble.
 
  • Like
Likes Delta2 and FactChecker
  • #17
In fact, the Moon’s orbit has an eccentricity of 0.055, meaning its distance will vary about 10% between perigee and apogee. (Earth’s orbit around the common CoM will have the same eccentricity.)

Because of this, you can have things like annular solar eclipses when the Moon is too far away to cover the full Sun due to the umbra not reaching the Earth’s surface, but the antumbra doing so.
 
  • Informative
Likes Delta2
  • #18
Delta2 said:
[*]Earth's orbit isn't perfect ellipse because classically there is the gravitational field of moon and possibly of Mars and Venus which affect it
As mentioned above we usually separate out the effects of the Moon and consider the orbit of the (barycentre of the) Earth-Moon system.

Neither Mars nor Venus have a great impact on this: I haven't checked but from memory the main classical factors causing deviation from an ellipse for the Earth-Moon system orbiting the Sun are in descending order:
  • Jupiter
  • Saturn
  • Other planets combined
  • Tidal effect of Sun on Earth-Moon system
  • Solar quadrupole moment (the equatorial bulge of the sun)
  • Tidal effect of Earth-Moon system on Sun
 
  • Informative
  • Like
Likes Ibix, FactChecker, Orodruin and 2 others
  • #19
Even in the Newtonian model and in the absence of other planets, the barycenter of the Earth-moon pair would not follow a perfect ellipse in its path around the Sun.

Newton's shell theorem allows us to treat the gravitational effect of a system as if it were a point mass, so as long as the system is spherically symmetric. The Earth-moon system is not spherically symmetric.

Edit: this would be the "Tidal effect of the Sun on the Earth-moon system" in the post just preceding.
 
  • Like
  • Informative
Likes pbuk and FactChecker
  • #20
drmalawi said:
Do you have a sound file available so that I can LISTEN to them?
Maybe this?

 
  • Haha
Likes Delta2 and malawi_glenn

Related to Earth's orbit not perfect ellipse

1. Why is Earth's orbit not a perfect ellipse?

Earth's orbit is not a perfect ellipse because of the gravitational pull of other planets and celestial bodies. These gravitational forces cause the shape of Earth's orbit to vary slightly over time.

2. How does the shape of Earth's orbit affect our seasons?

The shape of Earth's orbit does not directly affect our seasons. The tilt of Earth's axis is the primary factor in determining our seasons. However, the shape of Earth's orbit does affect the length of our seasons, as it determines the amount of time Earth spends closer or farther away from the sun.

3. Is Earth's orbit becoming more circular or more elliptical over time?

Earth's orbit is not changing significantly over time. It remains relatively stable, with only small variations in its shape due to the gravitational pull of other celestial bodies.

4. How do scientists measure the shape of Earth's orbit?

Scientists use a variety of methods to measure the shape of Earth's orbit, including astronomical observations, mathematical models, and satellite data. These methods allow scientists to track the changes in Earth's orbit over time and determine its overall shape.

5. Could Earth's orbit ever become a perfect circle?

No, Earth's orbit will never become a perfect circle. The gravitational pull of other celestial bodies will always cause some variation in the shape of Earth's orbit. Additionally, Earth's orbit is influenced by other factors such as the sun's gravitational pull and the distribution of mass within our solar system, which also prevent it from becoming a perfect circle.

Similar threads

Replies
4
Views
936
  • Astronomy and Astrophysics
Replies
33
Views
4K
Replies
17
Views
2K
Replies
3
Views
1K
  • Astronomy and Astrophysics
Replies
10
Views
2K
  • Astronomy and Astrophysics
Replies
3
Views
2K
  • Astronomy and Astrophysics
Replies
8
Views
2K
  • Astronomy and Astrophysics
Replies
8
Views
2K
  • Engineering and Comp Sci Homework Help
Replies
2
Views
2K
Back
Top