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polytech · Jul 28, 2008, 06:42 PM

I recently read that, because of our sun's orbit around the center of our galaxy, it moves appproximately 45 AU for every Earth year.

Since the radius of our orbit is approximately 1 AU, does that mean the true path of the earth is a stretched-out curlycue akin to a banana curl?

Polytech

Capuchin · Jul 29, 2008, 02:05 AM

Yup, also our galaxy is orbiting the center of the local group, and the local group is orbiting the center of the local supercluster.

polytech · Jul 29, 2008, 02:26 AM

So, is our orbit on the same plane as the sun's orbit? I am assuming that different planes would produce a somewhat conical orbit.

If it is, aren't we essentially playing leap-frog with the sun..

Also, do these vectors cause us to have an elliptical orbit?

Capuchin · Jul 29, 2008, 03:14 AM

The solar system is tilted almost 90 degrees to the plane of the galaxy. So you can imagine a kind of helix.

I'm not sure what you're saying about elliptical orbit - All orbits are elliptical.

polytech · Jul 29, 2008, 04:51 AM

Originally Posted by Capuchin

...

I'm not sure what you're saying about elliptical orbit - All orbits are elliptical.

We have man-made satellites in geostatic orbits, which are circular. They show that elliptic[ality?] isn't necessary to maintain an orbit.

I just wondered if the sun's motion vector(s) had the effect of stretching (at aphelion) & compressing (at perihelion) what would have otherwise been a circular orbit

ebaines · Jul 29, 2008, 06:45 AM

In the 2-body model of orbital mechanics (per Kepler and Newton) all orbits are elliptical. A circle is merely a specialized case of an ellipse.

Of course in reality there are multiple bodies in the solar system, each of which affects all the others, so that no planet or satellite moves in a truly elliptical orbit. Also, relativistic factors can affect an orbit as well - for example Mercury precesses in its orbit at a rate that can be shown to be caused by the effects of relativity.

For your satellite in geosynchronous orbit around the earth, the effects on its orbit due to the gravitational influence of the moon and sun would affect its orbit in a much, much bigger way than the gravitational influence of the rest of the galaxy- just as earth's tides are influenced by the sun and the moon, but not to any appreciable extent by any other bodies in the solar system, or the rest of the Milky Way galaxy.

polytech · Jul 30, 2008, 01:16 AM

Originally Posted by Capuchin

The solar system is tilted almost 90 degrees to the plane of the galaxy. So you can imagine a kind of helix...

If the sun's motion is on the X-axis and the galactical orbital plane is on the XZ plane, would the solar system's orbital plane be closer to the XY plane or the YZ plane?

It sounds like you are saying the latter.

If it is the latter, wouldn't the sun lead the solar system, like a cone?

Capuchin · Jul 30, 2008, 05:07 AM

Yes. YZ plane.

The Sun, I guess (this is just an educated guess), would indeed lead the solar system because gravity only travels at the speed of light. However the amount of lead is small. The sun travels around the galaxy center at about 240 km/s, so in the 8 minutes it take gravity to get from the sun to the earth the sun has moved on by about 115,000 km. That's about 1/12th the diameter of the sun. So a very very flat cone. By the time you get out to Neptune you're talking a couple of sun diameters lead.

polytech · Jul 30, 2008, 09:08 PM

Originally Posted by Capuchin

Yes. YZ plane.

The Sun, I guess (this is just an educated guess), would indeed lead the solar system because gravity only travels at the speed of light...

That is the first time I have ever heard of gravity traveling:confused: . I always thought, being a force, its presence and effects were instantaneous..!

Capuchin · Jul 31, 2008, 02:33 AM

Originally Posted by polytech

That is the first time I have ever heard of gravity traveling:confused: . I always thought, being a force, its presence and effects were instantaneous...!?

Of course not. Nothing moves faster than the speed of light.

That's the only mechanism by which I could imagine your cone happening.. How did you imagine it would occur?

polytech · Jul 31, 2008, 02:39 PM

I supposed that the vector of the Sun (accelerating around the center of the galaxy) and the vector of the Earth (accelerating toward the Sun) would form the legs of a right triangle. And that the lateral motion of the Earth's orbit would change that resultant vector into a cone...

Capuchin · Jul 31, 2008, 03:57 PM

Originally Posted by polytech

I supposed that the vector of the Sun (accelerating around the center of the galaxy) and the vector of the Earth (accelerating toward the Sun) would form the legs of a right triangle. And that the lateral motion of the Earth's orbit would change that resultant vector into a cone...

Hm, I can't quite picture it, are you picturing their acceleration vectors? The plane is in the YZ though so it would just form a helix, not a moving cone.. Please feel free to clarify :)

polytech · Jul 31, 2008, 04:53 PM

Originally Posted by Capuchin

Hm, I can't quite picture it, are you picturing their acceleration vectors?

Yes.

The plane is in the YZ though so it would just form a helix, not a moving cone.. Please feel free to clarify :)

If the Sun wasn't moving, the Earth's orbital plane would just reside in what we have identified as the YZ plane. The Sun would be at (0, 0, 0) and the Earth's orbit would be roughly (0, delta y, delta z). But if the Sun is accelerating away from (0, 0, 0) toward (delta x, 0, 0), Earth's given position (0, delta y, delta z) away from (0, 0, 0) and the Sun's new position (delta x, 0, 0) relative to (0, 0, 0) would form two legs of a right triangle. The Earth's tangential motion to the resultant hypotenuse vector would make it form a cone, just like rotating a plumbline while accelerating away from ITS center.

ebaines · Jul 31, 2008, 07:15 PM

It seems that you are assuming that the sun is being pulled by the gravity from the galaxy, but the planets aren't. But in fact any acceleration that the sun experiences due to gravitational influence of the rest of the galaxy will also be experienced by the planets orbiting the sun. Hence each of the planets have that same delta x component as the sun, and the planets remain in a plane about the sun. Does that help make it clear?

polytech · Jul 31, 2008, 07:36 PM

Originally Posted by ebaines

It seems that you are assuming that the sun is being pulled by the gravity from the galaxy, but the planets aren't. But in fact any acceleration that the sun experiences due to gravitational influence of the rest of the galaxy will also be experienced by the planets orbiting the sun. Hence each of the planets have that same delta x component as the sun, and the planets remain in a plane about the sun. Does that help make it clear?

I think so. Would that be like two spheres with the same diameter, but different densities, falling at the same rate?

polytech · Nov 24, 2008, 09:40 AM

Follow-up Question:

Is the solar system headed more north or south?

ebaines · Nov 24, 2008, 10:43 AM

Please clarify your question. Do you mean: as the solar system orbits about the center of the Milky Way Galaxy, what is our direction of motion? The center of the galaxy is in the direction of Saggitarius, and we are moving at approximately right angles to that in the direction of the star Vega in Hercules. Vega is located at 38.78 degrees north of the equator, so the solar system is moving more north than south as we circle the galaxy.

See: Milky Way - Wikipedia, the free encyclopedia

polytech · Nov 24, 2008, 11:16 AM

You gave the answer I was looking for. Earlier in this question, it was stated that the Earth's plane of orbit was approximately at a right angle to the Sun's present galactic motion, but it wasn't clear which of the two directions that was.

Thank you for your prompt response.