Prove that the earth goes around the sun

rattis · Mar 2, 2004

I find it obvious, as did many previous people, that the sun goes aroudn the earth. I of course know htis to be untrue as it has been drummed into me again and again for the past 16 years.

Can someone please prove to me (so that i can prove to others as well) that the Earth goes around the sun. Do not be afraid to explain using mathematics, as i see that as the only way of undeniable proof.

selfAdjoint · Mar 2, 2004

The parallax proof - empirical

The first person who had experimental evidence for this was the astronomer F.W. Bessel who in 1838 was able to measure the parallax of a nearby star. This showed that the Earth was at a different place, relative to the star, in June than it was in January. And geometry showed that the two places were on opposite sides of the sun. More parallax measurements since his time have confirmed that the Earth follows a closed path around the sun.

Phobos · Mar 2, 2004

Welcome to Physics Forums, rattis.

It certainly looks like it, doesn't it? But looks can be deceiving.

The "aberration of starlight" was the definitive proof of the heliocentric solar system.
http://www.encyclopedia.com/html/a1/aberstrlt.asp

And then there's all the spacecraft we send around the solar system which (1) successfully reach their destinations based on a heliocentric model of the solar system and (2) take photographs showing the sun at the center.

If you accept the values for the mass of the Earth and Sun, then the laws of gravity & planetary motion show you that the orbit around the common center of mass is near the center of the sun, not the Earth.

There are other evidences too...

Zero · Mar 2, 2004

You can start with basic gravitational theory, throw in a little bit of ballistics and orbital mechanics, and of course our successful navigation of craft through the solar system, all of which show conclusively that the Earth orbits the sun.

Canute · Mar 2, 2004

I thought the doctrine of Galilean relativity asserted that we couldn't know which orbited which. The maths is a lot easier in a heliocentric solar system, but that doesn't in itself entail that it is one. Surely all we know is that a heliocentric solar system is a very useful assumption? Or is this nonsense?

Zero · Mar 2, 2004

Originally posted by Canute
I thought the doctrine of Galilean relativity asserted that we couldn't know which orbited which. The maths is a lot easier in a heliocentric solar system, but that doesn't in itself entail that it is one. Surely all we know is that a heliocentric solar system is a very useful assumption? Or is this nonsense?

Just because it is a useful assumption, that does not mean it is nonsense. If both views are assumptions, but one is more useful and practical, guess which one we should go with?

Plus, of course, I'm not sure if Galilean relativity even applies?

rattis · Mar 2, 2004

And then there's all the spacecraft we send around the solar system which (1) successfully reach their destinations based on a heliocentric model of the solar system and (2) take photographs showing the sun at the center.

well yes, but i don't know if the spacecarft have every acctually gone into space or if it is just a con by government (worse case sinario).

Can i see some mathematical proof that the Earth does infact go around the sun?. Like i say the only proof i have at the moment is that i can see the sun move around the Earth everyday, but this is not the case as everyone says.

I am not an astronomer but mathematician, so I am not sure if this whould be in the maths section

just edited to fix quote tag - Phobos

Zero · Mar 2, 2004

Originally posted by rattis

And then there's all the spacecraft we send around the solar system which (1) successfully reach their destinations based on a heliocentric model of the solar system and (2) take photographs showing the sun at the center.

well yes, but i don't know if the spacecarft have every acctually gone into space or if it is just a con by government (worse case sinario).

Can i see some mathematical proof that the Earth does infact go around the sun?. Like i say the only proof i have at the moment is that i can see the sun move around the Earth everyday, but this is not the case as everyone says.

I am not an astronomer but mathematician, so I am not sure if this whould be in the maths section

You may as well give up, if you have to try to account for people who think the entire space program is a lie...

Canute · Mar 2, 2004

Originally posted by Zero
Just because it is a useful assumption, that does not mean it is nonsense.

I didn't suggest that the assumption was nonsense. I was wondering if what I said was nonsense.

but one is more useful and practical, guess which one we should go with?

No argument - but it's not really relevant.

Plus, of course, I'm not sure if Galilean relativity even applies? [/B]

No I'm not either, that's what I'm checking. But I can't immediately see why not, it's relative motion after all.

Phobos · Mar 2, 2004

Originally posted by Canute
I thought the doctrine of Galilean relativity asserted that we couldn't know which orbited which. The maths is a lot easier in a heliocentric solar system, but that doesn't in itself entail that it is one. Surely all we know is that a heliocentric solar system is a very useful assumption? Or is this nonsense?

At the time of/preceding Galileo, you could model it (the motion of the planets, etc.) very well either way. But the aberration of starlight nailed the sun down in the center with the Earth going around it. (that required very precise telescope measurements...something not available at the time of Galileo)

Phobos · Mar 2, 2004

Originally posted by rattis
well yes, but i don't know if the spacecarft have every acctually gone into space or if it is just a con by government (worse case sinario).

Can i see some mathematical proof that the Earth does infact go around the sun?. Like i say the only proof i have at the moment is that i can see the sun move around the Earth everyday, but this is not the case as everyone says.

I am not an astronomer but mathematician, so I am not sure if this whould be in the maths section

Diehard skeptic, eh? Check the math on parallax & aberration of starlight. (Google search or wait for some helpful PF member to present it here.)

Canute · Mar 2, 2004

Originally posted by Phobos
At the time of/preceding Galileo, you could model it (the motion of the planets, etc.) very well either way. But the aberration of starlight nailed the sun down in the center with the Earth going around it. (that required very precise telescope measurements...something not available at the time of Galileo)

Thanks. Can you explain that aberration a bit?

Nereid · Mar 3, 2004

rattis,

If you want a mathematical proof, completely disconnected from any observation or experiment, then you'll be disappointed - without any observations at all, you can't even know of the existence of the Sun, Moon, or even the Earth!

If you distrust everything that you read, and need proof of your own, you can do the stellar aberration experiment yourself. You could buy the equipment, probably for less than the cost of an average US house, or make it all yourself, from scratch. You may find an interested physics teacher at a nearby high school, who would welcome the chance to have her class take part in some real, 'hands-on' physics, so you could have the benefit of a critical audience.

Canute (and rattis) -> A one page, mathematical introduction to stellar aberration.

Canute · Mar 4, 2004

Thanks, I'll try to understand it. However I'm not sure it proves anything other than that if one assumes that the sun is going around the Earth then one must also assume that the stars are as well.

selfAdjoint · Mar 4, 2004

How do you feel about the Earth's rotation on its axis? Skeptical there too? Look up Foucalt's pendulum and coriolis force. If you can accept the Earth's rotation then it affects you candidate idea that the stars go around the earth.

The point is that it's your responsibility, denying the common wisdom, to come up with a self consistent alternative. If you can't find one, that in itself is an argument for the orbiting earth.

Incidentally, parallax shows that the stars move relative to the Earth in an annual cycle, and abberation shows that light moves relative to the Earth in an annual cycle (90^o out of phase with the first one). If you assume the Earth stationary, then these are two curious unexplained facts, but if you assume it orbits, then it is explained, the Earth is moving relative to the stars and as it moves its speed causes the abberation of light. Even the phases are in sync.

Canute · Mar 4, 2004

Originally posted by selfAdjoint
How do you feel about the Earth's rotation on its axis? Skeptical there too?

Not at all. Spin is a different case. (BTW I'm not skeptical about
the fact the the Earth goes around the sun, just wondering about whether it is the only way of interpreting the facts. I understood that with enough Ptolemaic circles you could model a stationary earth).

The point is that it's your responsibility, denying the common wisdom, to come up with a self consistent alternative. If you can't find one, that in itself is an argument for the orbiting earth.

That's the possibility I'm exploring.

Incidentally, parallax shows that the stars move relative to the Earth in an annual cycle, and abberation shows that light moves relative to the Earth in an annual cycle (90^o out of phase with the first one). If you assume the Earth stationary, then these are two curious unexplained facts, but if you assume it orbits, then it is explained, the Earth is moving relative to the stars and as it moves its speed causes the abberation of light. Even the phases are in sync. [/B]

Surely some fancy maths could sort that out, based on a stationary Earth and an orbiting universe? I agree that it would a peverse way of looking at it, but it seems possible.

Adam · Mar 4, 2004

Originally posted by rattis
I find it obvious, as did many previous people, that the sun goes aroudn the earth. I of course know htis to be untrue as it has been drummed into me again and again for the past 16 years.

Can someone please prove to me (so that i can prove to others as well) that the Earth goes around the sun. Do not be afraid to explain using mathematics, as i see that as the only way of undeniable proof.

I'm not going to read the whole thread, so I apologise if someone has already properly answered this.

Rattis, the Earth and Sun both spin around the common centre of mass, called the barycentre, or baricentre. Exactly the same as if you hold hands with someone and both spin around each other, leaning out.

Canute · Mar 4, 2004

Off topic but re. your signature - have Americans really all volunteered to be fingerprinted by their government? I find that impossible to believe. Weren't there any riots?

Phobos · Mar 4, 2004

Originally posted by Phobos
At the time of/preceding Galileo, you could model it (the motion of the planets, etc.) very well either way. But the aberration of starlight nailed the sun down in the center with the Earth going around it. (that required very precise telescope measurements...something not available at the time of Galileo)

Oops...aberration of light was the first major evidence and then stellar parallax nailed it down.

Phobos · Mar 4, 2004

Originally posted by Canute
Off topic but re. your signature - have Americans really all volunteered to be fingerprinted by their government? I find that impossible to believe. Weren't there any riots?

No. "The Onion" (source of that quote) is a website that makes up fictional/funny news stories.

http://www.theonion.com/index.php?i=1

LURCH · Mar 4, 2004

Originally posted by Canute
Surely some fancy maths could sort that out, based on a stationary Earth and an orbiting universe? I agree that it would a peverse way of looking at it, but it seems possible.

According to relativity, there is no difference between an orbitting Earth in a stationary universe and a stationary Earth with the universe rotating around it; they are the exact same situation viewed from two different frames of refference.

selfAdjoint · Mar 4, 2004

Originally posted by LURCH
According to relativity, there is no difference between an orbitting Earth in a stationary universe and a stationary Earth with the universe rotating around it; they are the exact same situation viewed from two different frames of refference.

Um, I don't think these accelerated (rotating) frames can be equated so simply via special relativity. And if you're thinking of the equivalence principle, remember that's only true in the limit; in extended frames tidal effects will easily detect which frame is moving. Note that Mercury, for example, revolves in the Schwartzschild geometry near the Sun, not the other way around.

Nereid · Mar 5, 2004

"The dipole signal seen by an observer moving with speed [tex]v[/tex] relative to the rest frame of the CMB is [tex]T_0 v/c[/tex], where [tex]T_0[/tex] is the absolute temperature of the CMB, and [tex]c[/tex] is the speed of light. Thus, additional sources of error that could affect the absolute calibration of the WMAP data include errors in the determination of WMAP’s velocity with respect to the solar system barycenter (the point of reference for the COBE dipole) and errors in the absolute temperature of the CMB. The velocity of WMAP is routinely measured with respect to geocentric inertial coordinates (GCI) with an accuracy of < 1 cm s^-1. The velocity of the Earth is determined from the JPL ephemeris with similar accuracy."
http://lambda.gsfc.nasa.gov/product/map/pub_papers/firstyear/syserr/wmap_syserr.pdf

Pity rattis, (s)he will have to build and launch a space probe like WMAP to convince him/herself that the Earth moves around the barycentre (so Jupiter's, Saturn's etc motion is included), as measured against the CMB.

Canute's model of the universe will have not only horribly complex orbits of the solar system planets (and asteroids, comets etc), but a very odd semi-annual ~2.73 K blackbody that goes round the Earth is just the same plane as the Sun does, but is clearly not connected to the Sun!

In principle, you could make observations of the CMB from the surface of the Earth, but ...

So, other indicators of semi-annual motion?

- pulsars (you have to know where you are wrt the barycentre to get the timing right - in fact, rattis could build a telescope, fit a webcam and good clock, and measure the Earth's motion quite accurately, all by looking at M1, the Crab pulsar!)
- (BTW, really good, coordinated observations by LBI radio telescopes will also show the ~200 million year motion of the solar system around Sag A*)
- doppler signals etc from the Voyagers and Pioneers (I think there's only one still broadcasting)
- fast binary timing (this is a variation on pulsars, but with quite different objects, and different physics)
- interstellar meteor streams (yes, we do have samples of particles from other stellar systems, burning up in the atmosphere every few seconds)
- doppler shifts in stars all around the celestial sphere, with a 6 months' period, and a magnitude which exactly matches a model of the Earth in orbit around the barycentre, in a plane pole at coordinates ([tex]\alpha, \delta[/tex]), ellipticity e, nodes at ...

Canute · Mar 5, 2004

Does this mean that orbital motion is not relative?

rattis · Mar 5, 2004

Ok. Is there any proof of this topic from a few hundred years ago? using just observations from Earth and mathematics?

I am sorry to be a sceptic, but generally until i have proof i do not believe.

Nereid · Mar 5, 2004

Originally posted by Canute
Does this mean that orbital motion is not relative?

To reinforce something which SelfAdjoint said, there are solid observations of the extent to which the Sun's mass 'bends' spacetime, and they match the predictions of GR to at least 1 part in 20,000.

Perhaps your question could be restated as "are there preferred frames of reference in GR?"

Nereid · Mar 5, 2004

Originally posted by rattis
Ok. Is there any proof of this topic from a few hundred years ago? using just observations from Earth and mathematics?

I am sorry to be a sceptic, but generally until i have proof i do not believe.

Do you mean before stellar aberration and parallax? Do you mean 'in principle, using only the technology available in 1704'?

While not quite in the same class as parallax and stellar aberration, Olaus Roemer's observations of eclipses of the Jovian moon Io should also help convince skeptics.

If you want 'proof', why don't you build a telescope, a webcam system, buy an accurate clock, and do the observations of the light pulses from the Crab pulsar yourself? It won't be expensive, is well within the technical reach of an amateur astronomer, and the maths is straight-forward.

Phobos · Mar 5, 2004

Originally posted by rattis
Ok. Is there any proof of this topic from a few hundred years ago? using just observations from Earth and mathematics?

I am sorry to be a sceptic, but generally until i have proof i do not believe.

Hey, we love skeptics. Many of us are skeptics. But skepticism is not disbelief of everything until you obtain absolute proof. There are scales of certainty and granting "acceptance" of theories (scientific theories being the explanatory models that a consensus of the world's experts agree best fit the experimental evidence...and knowing that theories will continue to be tested and refined). Skepticism is a weighing the available evidence (critical thinking) and putting your best foot forward. With hyper-skepticism, you'll be stuck forever on the question of whether reality exists or not.

Several proofs have been described here. You could take the simple equations for stellar parallax to suit your maths, but you will need to dig up the databases of temporal telescopic measurements of nearby & distant stars to see that the data show that nearby stars show more motion relative to us than the distant stars do. Or you could take the equations from the laws of planetary motion/gravity to calculate that the center of mass is by the sun, not the Earth.

Hmm...sudden thought...what kind of gravitational torque would be placed on the Earth if it was the center of the universe? Would it tear the Earth apart?

russ_watters · Mar 5, 2004

Has anyone mentioned http://alpha.lasalle.edu/~smithsc/Astronomy/retrograd.html ? Accepted or not, the Ptolemaic model was deeply flawed right from the start.

The problem of retrograde motion has been known for milenia and the explanation is elementary school simple. IMO, the main thing that kept people from figuring it out sooner was a blind following of Aristotle.

Nereid · Mar 5, 2004

'proof'? this is science!

Originally posted by rattis
Ok. Is there any proof of this topic from a few hundred years ago? using just observations from Earth and mathematics?

I am sorry to be a sceptic, but generally until i have proof i do not believe.

Forgot ... 'proof' works in mathematics; in science the paradigm (don't you just love that word?) is 'falsification'. The strongest statement you can make in science is something like: "all observations and experiments are consistent with X" (X is a theory), or "there are no repeatable observations or experimental results which are inconsistent with the predictions of X".

So, in the case of the Earth and the Sun, something like: all observations are consistent with {description of the Sun, including its mass}, {description of the Earth}, (etc, naming the planets and major moons) orbiting {description of the solar system barycentre} as predicted by GR.

rattis or Canute may make an observation tomorrow which is inconsistent with GR; bye-bye GR! (Of course, for such a dramatic consequence, there'd be dozens of folk who'd want to repeat the observations, to convince themselves).

selfAdjoint · Mar 5, 2004

Originally posted by russ_watters
Has anyone mentioned http://alpha.lasalle.edu/~smithsc/Astronomy/retrograd.html ? Accepted or not, the Ptolemaic model was deeply flawed right from the start.

The problem of retrograde motion has been known for milenia and the explanation is elementary school simple. IMO, the main thing that kept people from figuring it out sooner was a blind following of Aristotle.

Eudoxos' homocentric spheres theory explained retrograde motion but didn't quantify it. Appolonios of Perga's deferents and epicycles explained retrograde motion and Hipparchos and eventually Ptolemy did quantify them/it. The only problem with the theory as Ptolemy left it was the motions in latitude. That plus the problem of the rate of motion. Ptolemy used a trick (arbitrary) called bisection of the equant to get a form of uniform motion to match the motion we now know to be governed by Kepler's second law.

The Ptolemaic theory could have been cleaned up (a la Tycho Brahe's model), but by the time Tycho died everybody but superskeptics and religious bigots had accepted heliocentrism.

Canute · Mar 6, 2004

Originally posted by Nereid
So, in the case of the Earth and the Sun, something like: all observations are consistent with {description of the Sun, including its mass}, {description of the Earth}, (etc, naming the planets and major moons) orbiting {description of the solar system barycentre} as predicted by GR.

This is is the issue really. I'm not a sceptic, and certainly not suggesting that the Earth goes around the sun. (After all Nicole d'Oresme worked that, and 'Galilean' relativity, in the fourteenth century, pretty much by logic alone).

What you say here is true. But my question was whether all observations are also consistent with a description in which the Earth is at the centre, however mathematicallty strange that theory would have to be.

Nereid · Mar 6, 2004

Originally posted by Canute
This is is the issue really. I'm not a sceptic, and certainly not suggesting that the Earth goes around the sun. (After all Nicole d'Oresme worked that, and 'Galilean' relativity, in the fourteenth century, pretty much by logic alone).

What you say here is true. But my question was whether all observations are also consistent with a description in which the Earth is at the centre, however mathematicallty strange that theory would have to be.

It may well be fun to try to build a detailed mathematical model which accounts for parallax, stellar aberration, the Shapiro time delay (yes, that can be observed in a one-way observation, no need for spaceprobes), bending of light, semi-annual doppler shifts, etc, etc and explicitly starts with the Earth as the centre of the universe.

However, I doubt that it'd be very interesting. For a start, it would have to assume that little or none of the physics we observe in labs here on Earth applied to any of the things which our Heath Robinson model contained. Further, every time anything new was observed - gamma ray bursts, for example (yes, you can detect those from down here on the surface of the Earth, no satellites required) - you'd have to build new physics to handle it!

Oh, and you can forget such useful things as GPS and communications satellites - not only couldn't you launch them (unlikely rockets could make it out of the atmosphere, given that 'outside Earth' physics would be so different), but they wouldn't work (again because the physics would be too different).

selfAdjoint · Mar 6, 2004

Originally posted by Canute
This is is the issue really. I'm not a sceptic, and certainly not suggesting that the Earth goes around the sun. (After all Nicole d'Oresme worked that, and 'Galilean' relativity, in the fourteenth century, pretty much by logic alone).

What you say here is true. But my question was whether all observations are also consistent with a description in which the Earth is at the centre, however mathematicallty strange that theory would have to be.

Canute, have you got a site for Oresme and the Earth going around the sun? I know he discussed a rotating model of the earth, but I never heard of the other.

My understanding of the discussion of the rotating Earth in the 14th century is as follows: The philosopher Buridan had developed a concept of what we might call "naive momentum", which was sort of proportional to weight and speed, and sort of conserved (he described it in commentaries on Aristotle, so you have to read it carefully to see what he means). At any rate he gave the example, contra Ptolemy, of an object thrown up from the surface of a rotating earth.

Ptolemy had said it would fall behind the thrower, since he, attached to the earth, would be moving, while the object, freed from earth, would in accordance with Aristotle's physics, have no translational motion. But Buridan said that the object would still have his "impetus", which would keep it moving to fall in the same place as if the Earth were at rest. So it was Buridan who introduced the basic Galilean relativity.

Oresme, who was basically a mathematician, then wrote a treatise observing that an object projected sufficiently high, even though it retained its impetus, would have the speed associated with that impetus less than the speed required of objects at that greater radius, to keep up with the rotating surface of the earth. So the object would too fall behind.

Assume the experiment takes place at the equator. Then the point of projection would move with whatever speed the rotating Earth gave, v, during the time the object rose and fell, t, so a distance vt. And this would be at the distance R from the Earth's axis, so the point of projection's path would subtend there an angle of arctan(vt/R). Meanwhile, the object's average height during its rise and fall would be h, and it would travel horizontally the same distance as the point of projection, vt. Thus its path would subtend the angle at Earth's axis arctan(vt/(R+h)), which is obviously smaller than the first one, so the object would fall behind the point of projections's new position.

Canute · Mar 7, 2004

Originally posted by Nereid

Perhaps your question could be restated as "are there preferred frames of reference in GR?" [/B]

Pehaps this is what I should have asked.

Prove that the earth goes around the sun

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