# Revolution of earth around sun

wvguy8258
I got into an argument with someone over Earth revolving around the sun vs sun revolving around the earth. He stated that there are reference points within the universe where the sun appears to revolve around the Earth that are NOT on the surface of the earth. I conceded that perhaps a point in geosynchronous orbit would appear to have the Earth revolving around it and the sun revolving around the earth. I then stated that you would be accelerating though in this orbit. He stated that there are 'fixed' points where you would not be accelerating and that the sun would be seen revolving around the earth. Is he correct?

Homework Helper
Not entirely sure what you mean.
You could claim that the Sun orbits around the Earth but you would still have the other planets revolving around the sun.
You would also have to explain the apparent motion of everything else in the universe.

Gold Member
Your friend has a point in that neither "goes around" the other, exclusively.
Any two objects can be considered as being on orbit about their combined centre of mass. In the case of the Earth and Sun, the cm of the pair is as near dammit to the centre of the Sun. In the case of the Earth and Moon (more similar in size), the cm is at a point below the Earth's surface but a significant distance from its centre - hence the wobble, which causes the tides to have two bulges - one towards the Moon and the other one away from it.

Gold Member
Not entirely sure what you mean.
You could claim that the Sun orbits around the Earth but you would still have the other planets revolving around the sun.
You would also have to explain the apparent motion of everything else in the universe.

One step at a time: can you specify a "fixed" frame of reference that is not on the Earth wherein the sun appears to revolve around the Earth?

The question, of course, is: fixed with reference to what? If you fix your FoR to Earth then sure, but I think the OP is referfing to fixed wrt some external FoR. This would need to be specified.

wvguy8258
Not entirely sure what you mean.
You could claim that the Sun orbits around the Earth but you would still have the other planets revolving around the sun.
You would also have to explain the apparent motion of everything else in the universe.

I know. He doesn't want to hear this though. He wants to believe that the heliocentric model is just our bias. I know that einstein said all reference frames are equally valid. I think he is trying to capitalize on this.

Gold Member
In the case of the Earth and Sun, the cm of the pair is as near dammit to the centre of the Sun.

wvguy8258
Your friend has a point in that neither "goes around" the other, exclusively.
Any two objects can be considered as being on orbit about their combined centre of mass. In the case of the Earth and Sun, the cm of the pair is as near dammit to the centre of the Sun. In the case of the Earth and Moon (more similar in size), the cm is at a point below the Earth's surface but a significant distance from its centre - hence the wobble, which causes the tides to have two bulges - one towards the Moon and the other one away from it.

He didn't know this, I pointed it out. He is talking about full on the sun moving around the Earth in 24 hours, not moving around a common point.

Homework Helper
He doesn't want to hear this though. He wants to believe that the heliocentric model is just our bias

In that case it's pretty obvious that the universe revolves around my wife

wvguy8258
One step at a time: can you specify a "fixed" frame of reference that is not on the Earth wherein the sun appears to revolve around the Earth?

The question, of course, is: fixed with reference to what? If you fix your FoR to Earth then sure, but I think the OP is referfing to fixed wrt some external FoR. This would need to be specified.

A point not on Earth that is not accelerating. The only way I can see the sun appearing to revolve around the Earth (if not on the earth) is if this point somewhere (outside our solar system let's say) is accelerating around in order to make this be observed. He is trying to say that he could 'take me to alpah centauri' or something and show me that the sun revolves around the earth. I think he is full of it.

Gold Member
A point not on Earth that is not accelerating. The only way I can see the sun appearing to revolve around the Earth (if not on the earth) is if this point somewhere (outside our solar system let's say) is accelerating around in order to make this be observed. He is trying to say that he could 'take me to alpah centauri' or something and show me that the sun revolves around the earth. I think he is full of it.

What if it were merely turning about its own axis?

If you centred a scope on Earth, the sun could be seen to revolve around it...

I don't think your friend really understands that a rotating FoR is an accelerating FoR.

bjacoby
I got into an argument with someone over Earth revolving around the sun vs sun revolving around the earth. He stated that there are reference points within the universe where the sun appears to revolve around the Earth that are NOT on the surface of the earth. I conceded that perhaps a point in geosynchronous orbit would appear to have the Earth revolving around it and the sun revolving around the earth. I then stated that you would be accelerating though in this orbit. He stated that there are 'fixed' points where you would not be accelerating and that the sun would be seen revolving around the earth. Is he correct?

Look. This whole question is philosophical not physics. The question of what "revolves around" what requires that one know for certain that one of the items in question is in a truly fixed reference frame. If one item is fixed then the other one is clearly revolving around it. Your friend claims that there are some "fixed" points in the universe. So how exactly does he know this? Presumably he is claiming to know where the "fixed point" (stationary frame) of the universe is located. He can't know this. To know where the fixed point of the universe is one would have to be God and have knowledge of what is OUTSIDE the universe that it can be referenced to. This is all nonsense. Therefore in physics all frames are considered of equal validity. One can fix a frame to the Earth and claim that all things revolve around it, (as was done for so many years in the past) but how would one know if the Earth itself (and that attached frame) is hurtling through "all that is" or not? One can't. So it's a test of faith. OK?

Gold Member
I try to be precise! (Near enough for Jazz)

Gold Member
I try to be precise! (Near enough for Jazz)

I was poking fun at your cussing.

Gold Member
Look. This whole question is philosophical not physics. The question of what "revolves around" what requires that one know for certain that one of the items in question is in a truly fixed reference frame. If one item is fixed then the other one is clearly revolving around it. Your friend claims that there are some "fixed" points in the universe. So how exactly does he know this? Presumably he is claiming to know where the "fixed point" (stationary frame) of the universe is located. He can't know this. To know where the fixed point of the universe is one would have to be God and have knowledge of what is OUTSIDE the universe that it can be referenced to. This is all nonsense. Therefore in physics all frames are considered of equal validity. One can fix a frame to the Earth and claim that all things revolve around it, (as was done for so many years in the past) but how would one know if the Earth itself (and that attached frame) is hurtling through "all that is" or not? One can't. So it's a test of faith. OK?

I don't really think that's what this is about.

wvguy8258
No, I think this is what this is about, in a sense. Okay, so if in only one reference frame (earth-centered) it can be said that the sun revolves around the Earth and every other reference frame off the planet disagrees, then both claims are equally correct?