The orbital eccentricity change of the Earth ?

In summary, the eccentricity of the Earth's orbit is decreasing at a rate of ~-0.00004292/century and we can be sure of this through observations and measurements, as well as predicted effects based on physics. The accuracy of observation is very high, especially when taking into account the observations of other planets and their orbital solutions. This can also lead to the discovery of Milankovitch climate cycles on Earth and Mars. There are also direct observations that can be made to determine the distance to the sun, without needing to reflect radar off of it.
  • #1
Bjarne
344
0
Can someone answer one, some or all these questions;
  • Is the orbit of the Earth right now getting more circular or more elliptical?
  • How much?
  • How can we be sure?
 
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  • #2
The eccentricity of the Earth's orbit is decreasing at a rate of ~-0.00004292/century.
 
  • #3
Bjarne said:
Can someone answer one, some or all these questions;
  • Is the orbit of the Earth right now getting more circular or more elliptical?
  • How much?
  • How can we be sure?

We can be sure based on observations and measurements coupled with predicted effects based on physics.
 
  • #4
Drakkith said:
We can be sure based on observations and measurements coupled with predicted effects based on physics.

We can so far I know not measure the distance to the Sun because the Sun does not reflect radar.

So how accurate is “observation” ?
 
  • #5
Very accurate, actually. The trick is not to observe the Sun directly, but to observe the other planets, and to find a self-consistent orbital solution from these observations that agrees with General Relativity. One can even test for departures from GR and for unmodeled mass.

Once one does that, one can extrapolate the planets' motions several million years both forward and backward. When one does that, one finds that the planets' orbit orientations do loop-the-loops, and that their eccentricities and inclinations oscillate quasiperiodically. This leads to Milankovitch climate cycles on the Earth and likely also on Mars.

In particular, I've plotted

Eccentricity / Runge-Lenz vector: {e*cos(w), e*sin(w)}
Inclination / north-pole vector: {sin(i)*cos(W), sin(i)*sin(W)}

for the last several million years.

I've made videos for YouTube:
http://www.youtube.com/my_playlists?p=D0825FC30A2F00A6 [Broken]
http://www.youtube.com/my_playlists?p=86F2CCA7F3F677ED [Broken]

I got the numbers from here:
J. Laskar
"Secular evolution of the Solar System over 10 million years"
Astronomy and Astrophysics, 198, 341-362 (1988).
http://adsabs.harvard.edu/abs/1988A&A...198..341L

I had to OCR the numbers and then painstakingly correct the OCRing, so there might still be some typos.
 
Last edited by a moderator:
  • #6
Bjarne said:
We can so far I know not measure the distance to the Sun because the Sun does not reflect radar.

So how accurate is “observation” ?

There are direct observations that can be made to determine the distance to the sun. We don't need to reflect radar off of it.

See here for more info. http://curious.astro.cornell.edu/question.php?number=400 [Broken]
(Further down is how the 1st astronomers measured the distance to the sun)
 
Last edited by a moderator:

1. What is orbital eccentricity?

Orbital eccentricity refers to the shape of an orbit around a central body. It is a measure of how elliptical (or non-circular) the orbit is, with a value of 0 representing a perfect circle and a value of 1 representing a highly elongated ellipse.

2. How does the Earth's orbital eccentricity change?

The Earth's orbital eccentricity changes due to various factors, such as the gravitational pull of other planets, the shape of the Earth's orbit around the sun, and even the distribution of mass on the Earth's surface. These factors can cause tiny variations in the Earth's orbit, resulting in changes in the eccentricity over long periods of time.

3. What is the current orbital eccentricity of the Earth?

The current orbital eccentricity of the Earth is approximately 0.0167. This means that the Earth's orbit around the sun is slightly elliptical, with the distance between the Earth and the sun varying by about 3 million miles throughout the year.

4. How does orbital eccentricity impact the Earth?

The Earth's orbital eccentricity has a significant impact on our planet's climate and seasons. When the Earth is at its closest point to the sun (perihelion), it receives more direct sunlight, resulting in warmer temperatures and shorter seasons. When the Earth is at its farthest point from the sun (aphelion), it receives less direct sunlight, resulting in cooler temperatures and longer seasons.

5. Can changes in orbital eccentricity cause major climate shifts on Earth?

Yes, changes in orbital eccentricity can potentially cause major climate shifts on Earth. However, these changes occur over long periods of time (tens of thousands of years), and other factors such as the Earth's rotation and tilt also play a significant role in our planet's climate. Therefore, while orbital eccentricity can contribute to climate change, it is not the sole determining factor.

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