Astronomy questions from grandson I am unable to answer

[Chronos]

How does the relative masses have anything to do with the relative positions?

[Tim_T-Bonham.net]

@Chronos

How does the relative masses have anything to do with the relative positions?

Well, it’s gravity determining their positions, and the movement between them. And I seem to recall hearing that gravity was related to the mass of the objects. From a guy named Isaac Newton, originally. Do you have some other theory on this?

[Chronos]

Well, yes, but that doesn’t change the fact that the Earth is sometimes ahead of the Sun and sometimes behind it. How would it?

[naita]

I think t-bonham is answering the non-existent question four. How much does the speed of the Sun change when the Earth is ahead or behind? The answer is of course very little, but not as he/she writes imperceptible for any and all planets. That’s, after all, one of the methods used to find the first known exo-planets.

[Robot_Arm]

@OldGuy

Still further info: Apparently the plane of the ecliptic (the path of the earth around the sun) is at almost a right angle to the plane of the galaxy’s bulge (and plane of rotation) so there is really no time of the year in which the Earth is gong faster or slower than the Sun around the center of the galaxy. I assume this may change during the time it takes the Sun to orbit the galaxy, but that cosmic year is over 200 million years long so we’ll have a while before the story needs changing.

@Anne_Neville

From what I’ve seen, it’s more like a 60 degree angle than a 90 degree angle.

That the plane of the ecliptic is angled relative to the plane of the galaxy doesn’t tell the whole story. Let me see if I can explain what I’m seeing in my mind.

Picture a plane (A) defined by the sun’s path about the center of the galaxy. On that plane is a circle (O) representing that path, and a point representing the sun’s current location. Through that point there exists another plane (B) representing the ecliptic. The intersection of A and B defines a line (L), but we still need to know the orientation of L relative to O;[sup]1[/sup] it could be tangent to O, coincide with the radius of O, or be anywhere in between.

MikS’s link seems to show the line of intersection running toward the center of the galaxy in both the disputed and corrected versions of the animation. Is that correct?
1 I’m sure astronomers know this, I just don’t think we’ve nailed it down in this thread yet.

[JKellyMap]

@naita

In a system with more similar masses than the Earth and the Moon, the wobble is more pronounced. As you can see in the recent images of Pluto and Charon from the New Horizons mission: New Horizons Sees Pluto and Charon - NASA

Awesome!

[Anne_Neville]

@Robot_Arm

I’m sure astronomers know this, I just don’t think we’ve nailed it down in this thread yet.

Actually, this is tricky, because the astronomers who study the solar system don’t tend to be the same ones who study the galaxy. The sun’s crossing the galactic plane doesn’t have any noticeable effect. When the moon crosses the plane of the Earth’s orbit, you can get eclipses (if the moon is new or full). When the sun crosses the plane of Earth’s equator, you get the vernal or autumnal equinox. Those are things that people notice- so much so, that there have been records of them since ancient times. The sun crossing the galactic plane- not so much.

@Chronos

Well, yes, but that doesn’t change the fact that the Earth is sometimes ahead of the Sun and sometimes behind it. How would it?

It doesn’t. It does change how much the Earth wobbles due to the motion of the moon.