Does the Earth orbit around where the Sun was 8.5 mins ago?

[g__day]

Interesting thought huh? Gravity like all e-m radiation radiates at lightspeed. The Sun and Earth are each moving at about 60,000km/hr. Light from the Sun, like gravity from the Sun takes 8.5 minutes to reach us. In that time the Sun has moved about 8,000km from where we saw it.

If the Sun suddenly wasn't there we'd keep orbit around were it last was 8.5 minutes ago for 8.5 minutes until we noticed it was gone!

So isn't it strange, we are orbiting around the Sun we see - because its obivously the Sun were it was 8.5 minutes ago from our frame of reference. So move the Sun forward about 1/2 a Sun's diammeter in the sky - and that is where the Sun really is!

[ving]

er... are you taking into acount that the galaxy is rotating at about 240 km/s?
:P

[g__day]

No.

My frame of reference for this kinda cute example is just considering a Sun / Earth system; as all else for the purposes of this discussion is padding (its a irrelevant relative motion as there is no absolute set of spacial co-ordinates according to relativity).

Look at the Sun and you see it as it was 8.5 minutes ago relative to Earth time. We feel its gravity and see its position as it was 8.5 minutes ago too because that's how both the force carriers radiate and the warping of spacetime radiate in any relativistically compliant part of spacetime.

[sheeny]

G'Day g_day,

uh... I think you just answered your own question...:D

If there is no preferencial reference frame then the earth rotates around the sun. Period. Regardless of the motion of the Sun-Earth system through space the gravitational force between the two follows the same flux lines as the light from the sun to earth and as reflected from the earth to the sun. In the reference frame of the earth or the reference frame of the sun, these are the same path each way.

To an observer in a reference frame in uniform motion to the sun earth system, the light paths will differ. for example light passing from the sun to the earth and being reflected back will describe a saw tooth shape or "V" path... the same shape is made by a "gravity wave" or graviton (depending on the flavour gravitational theory you prefer today) leaving the sun to travel to the earth, but since gravity isn't reflected (is it?) we have to use the arrival of the first gravity wave or graviton from the sun as a trigger for a return one from the earth to the sun. This is a bit of a mental fabrication as gravity acts continuously:P .

All very hypothetical I think, because I'm not aware that the elusive "graviton" has been detected, nor have gravity waves???:shrug: Feel free to correct me anyone! As far as I know the actual mechanism of gravitational attraction hasn't been resolved yet, which is why there are different models from particle theory, string/brane theory and space time curvature...

Interesting little puzzle... Food for thought!:thumbsup:

Al.

[g__day]

Correct, the best way to see this is draw a circle or elipse. Place the Sun and Earth opposite each other somewhere on the circumference. Note this as there "real" positions. Now mark where an observer on the Sun see's the Earth, say a centimetre anti-clockwise, likewise mark where an observer on Earth sees the Sun, also a centimetre anti-clockwise. Repeat this for an point in time drawing a line between the "real" Earth and Sun positions and the relativistically observable Earth and Sun posiitons. For any points you get a stable, balanced system with a stable point of suspension, so the system doesn't collapse.

Nice how nature works out all the complex mathematics for us, isn't it! And as you noted, it wasn't a question, more an interesting observation of something I bothered to research about a year ago!

[ving]

i scared somone recently... it's amazing how we just take things for granted. I explained to someone at work that no matter where you look you are looking into the past...
"what! no way" came the exclamation.
the eye registers light and light travels at a finite speed so it would stand to reason that if you look at an object lightyears away or 4 meter the light still has to travel from the object to you eye...

I was working the lateshift with this person and the rest of the shift was spent in relative silence ;)

yeah i know this is relatively basic stuff but its stuff the average person doesnt think about :)

[xelasnave]

Is the conclusion "yes we orbit where the Sun was 8 mins ago?"
I see it that the Sun is the leader, Mercury Orbits, x mins "behind" Venus x+y mins "behind" Earth orbits 8 mins "behind" and so on so that edge on we have a cone like progression orineted like a pie in the face (although in reality inclined at an angle).This is a view constructed in my mind I dont know that is the way it is but it would seem if G is no faster than C we have not alternative. Does anyone know if this is the way it is..should use all the gear and figure it out myself from observations.
alex

[sheeny]

Alex,

It depends on the precision you want to consider the problem at, and the observers reference frame.

The motion of the sun through space is so close to uniform motion that we can assume the frame of reference is inertial. So the earth rotates around the sun... if the inertial frame of reference is moving with the sun, then yes... the earth rotates around where the sun was 8 minutes ago:D (which just happens to be the same place that it is now!!!;) ). If the inertial reference frame you observe the sun from is moving uniformly at a velocity not equal to zero relative to the sun, then the earth rotates around the sun and NOT where it was 8 minutes go.

In actual fact the sun is rotating around the centre of the milky way galaxy, and is subject to extremely small perturbations by nearby stars, so it is actually not moving in uniform motion in the most precise terms - it is subject to accelerations - but they are so extremely small! And since the distances between stars are so big compared to the earth-sun radius, the earth is subject to the same accelerations (which are essentially negligible).

So the short answer is... the earth rotates around the sun. i.e. a component of the velocity of the earth is the same as that of the sun.

Al.

[xelasnave]

Thanks for that..Are you a lawyer cause that sounds like "on the one hand we have etc..":lol: :lol: :lol:
I think I have a grip on the different frame. What is your opinion as to how the system travells thru space in a cone like formation?
alex

[sheeny]

Oh no I've blown my cover!:rofl:

No, Alex, I'm not a lawyer... at least not for man made laws! I'm a professional mechanical engineer, but sometimes I feel like I'm lawyer at work - trying to explain why some people's ideas break the laws of physics, so if they try to build it, the laws of nature will break what they built!:lol: (or it just won't work). It's surprising how many people think that because it's possible to break man made laws, it must be possible to break the laws of nature! Now there's some logic for you!

I think I suffer from terminal curiosity... I like to understand how things work and I like learning and exercising the grey matter, so often when I'm asked a question I have to decide whether or not to give the short answer, the long one or something in between. I was in a bit of a playful mood so I thought I'd lob something approaching the long answer just for fun...:P

Al.

[sheeny]

Not sure if I've heard that one...:shrug: Are you referring to the expansion of the universe when you talk about the cone like formation?

Al.

[xelasnave]

No I know what you refer to but unrelated although that is a cone it is a sortta "time cone".
In a solar system just like ours but without gravitational influence (the one that causes our (there I go claiming it in the name of humans) solar system to tilt).. in such a similar system the Sun travells across this page from left to the right, see the orbits of the planet edge on from out in space your chair will do, the orbits represented by lines from the top of the page to the bottom of the page..to scale seeing you are an engineer:D (and try to avoid more frames it is confusing enough at this point) Well my idea is that Mercury would orbit a central point say 5mms left of the Sun on the page and have a line ,to scale representing its orbit up and down ,vertical to be technical, Venus orbit a point say 8mm to the left of the Sun with an upand down orbit line , the Earth orbits a point centre 10 mm to the left of the Sun.and for each planet all the way out till we go off plan (so as not to try and explain them not being in the plane)
As such the orbits one behind the other and a little removed from the circle to its left or right each orbit forms a frame of a cone..the pointy end being the Sun and the last orbit mmm not Pluto because its off the plane but a body still in plane (Pluto probably cant figure out where the Sun is because the news is so old :lol: :lol: :lol: ) Pluto must in time fall into line like the other planets unless it is experiencing some gravity "push" that has not been observed...but do you see the cone now? If not I will draw something . I had a leagal background and find it hard to say anything simply so I will understand if my meaning is lost. The Orbits are top to bottom of the page if that makes it clearer. I understand the cone of creation but its nothing like that..get an ice cream cone and draw lines parrallel to the top the point being the Sun and each line further up the cone a planet a little further out (and up the cone) than the last...the system then travells with the pointy end first.. a pie in the face orientation I call it..our system does this I believe (subject as always new and better information) but is tilted from memory around 45 deg but thats unreliable..but more than 10 degrees one could expect.
alex

[sheeny]

Ah Alex I see what you mean.

The short answer is "no". :D

Unfortunately this all has to do with frames of reference again. Your arguments suppose that there is a preferential reference frame - the Michelson Morley experiement (I think:shrug: ??? Hope I got the right names!) proved that the "universal aether" didn't exist so there was no preferential reference frame, and this lead on to Einsteins theory of relativity.

So all inertial frames of reference (i.e. not being accelerated) are equally important and valid and the laws of physics can be transposed simply from one to the other.

So if the sun is moving at uniform speed from left to right because of our choice of reference frame, then all the planets also move from left to right at the same rate with it - because the motion is really the motion of our reference frame.

The way you are thinking about the problem only works if the sun is being accelerated across our computer screens (man, I'm going to have to get a baader filter so I can read this thing!:rofl: ) without the same accelerating force being applied to the planets. If the sun was to produce a huge jet out one side, we'd have your scenario exactly!

BTW I realised last night as I drifted off to sleep that my previous post with the references to all the reference frames in it, wasn't strictly correct! I forgot all about our moon!:rolleyes: The earth-moon system rotates around the sun, earth rotates around the sun with a wobble of amplitude equal to the radius from the earth's centre to the gentre of gravity of the earthmoon centre (earth-moon barycentre... is that the correct term?) and a frequency equal to the period of the moon (which period of the moon depends on your chosen reference frame again!:lol: ).

Al.

[xelasnave]

mmmm you really should have been a Lawyer:lol: :lol: :lol: .
I think the problem is with all this stuff I expect to see the picture God sees:shrug: ...
I must be missing something but I would have thought that we can see what I suspect or not. Each planet must lag behind the other otherwise we have to find a different speed for gravity. If all orbited on the same plan gravity must be instant if it travells at C well such a lag shoulld be present.
I will think more and re read what you have written and see if I can move forward:) .
thanks for your interest:thumbsup:
alex

[xelasnave]

What I mean is I suppose relativity enables us to stand back as it were and observe a frame and how it relates to another. Finally that says to me the system is able to interpret a situation not withstanding all we see is a little different to what we think we see. My point is a cone pattern should exist where in that frame we see the Sun and the planets moving in relation to space outside the solar system. Maybe that is wrong but I fail to see why.
alex

[sheeny]

Alex,

I think part of the problem is that we don't know what the mechanism of gravity really is. There are numerous models that I am aware of that are used to describe it in different contexts, but I don't think I've seen or heard of a definitive "gravity works this way". Please if someone can correct me on that, feel free!

Particle theory predicts the graviton, as does string/brane theory, relativity predicts gravity waves, etc but I don't know that anyone has actually detected a graviton or a gravity wave have they?

So even though relativity says nothing can travel faster than c, if we haven't found a gravity wave, how do we know that for sure? It might be the best model we have at present, but it doesn't mean that it's right. That's the whole basis of scientific method!:thumbsup:

I don't have a problem with the time cone concept, but I can't see how they can affect gravity. They will affect a signal in EM radiation, and they will affect the timing of a gravitation wave between observers at two locations (say earth and sun) but otherwise gravity is relentless. You can't turn it on and off, so to get the affect you described, you would have to accelerate the sun only and not the planets.

I haven't thought so much about this stuff in years! It's good to rummage through the cobwebs!:D

Al.

[xelasnave]

You have the point. The Sun is moving, it controls the game, where it goes the planets follow. Irrespective of how you percieve gravity we are on safe ground to this point. I have concluded that the only way the planets can move is by following the Sun, as it moves we have the opportunity to observe where the planets orbit, If gravity travells at a speed (in my explanation of gravity C is favoured but as it is particl based I may have to settle for a slightly slower speed:lol: ) there must be a lag for they are orbiting a Sun that was there minutes or hours ago. If the cone shape is present it would be easy to work out the speed of gravity. If it is not there (all planets orbit the Sun in a direct line in the pos it is) then it may be that gravity is instant. However this may also point to a property of gravity as acting like an instant glue on all the solar system (which is sortta like my gravity idea but I think C is probably the speed tha glue works at)..not very scientific but I am trying to convey quicky short ideas on a big subject.
Gravity is something that fasinates me and I read everything I get my hands on and would say this I have yet to see it explained as to how it works (other than my primative attemps here and at astronomy daily) Space time does nothing than describe the geometry of circles in square to be cruel. It does not offer any explanation why space is bent near mass...of course I do and fortunately other than wanting a particle to travel at C (impossible) its a good idea:lol: :lol: :lol: but I can almost fit space time because it is a measurement thing. Mind you I am only competeant in one dimention but that is a math ability thing, I think I understand it.
From what I can tell all the problems (graviton, dark matter neutrenio search etc and even my ideas) for gravity amount to needing a particle to have some mass which is in conflict with it travelling at C. That is all I have really worked out to date and others with pages of notes may take longer to explain the same conclusion I think.
I like the idea that gravity is really the pressure of other bodies upon each other and that any effect we observe as gravity is in effect an imbalance in that pressure caused by a shielding from the absolute pressure of the Universe.

alex

[sheeny]

G'Day Alex,

The equivalence of inertial reference frames is what you are missing, I think.

If the sun is truly stationary in space, do you agree that the planets rotate around th sun? Regardless of the speed of "action" of gravity, the sun is in the same place as it was 8 minutes ago or 10 years ago.

Now imaging we are travelling past the solar system perpendicular to the plane of the planets' orbits at a velocity v. We have no effect on the behaviour of the sun-planet system - the planet still rotates around the sun.

The equivalence of inertial (not accelerating) reference frames states this is true, and that it makes no difference if our reference frame was stationary and the sun's was moving.

Relative to our moving reference frame, both the sun and planets have the same velocity perpendicular to the plane of the orbits. They have momentum, and kinetic energy in that direction, and both these must be conserved because we are not applying a force to accelerate any of those bodies.

If the conical model you are thinking about was true, there would be a component of the gravitation force perpendicular to the plane of the planets. This component would cause a change in both the momentum and kinetic energy of the sun planet system, if this was the case in the formative period of the solar system, it can not be sustained without an external force acting selectively on the sun (say the jet out one side I suggested as a thought tool before), so the system would decay to the stable planar orbit we observe today.

I'm not sure I'm explaining myself very well...:shrug: Anyway, I hope its giving you something worthwhile and interesting to thin about!

Al.

[xelasnave]

Thanks Al
I cant admit to you I understand yet because I dont. I spent the day looking at things and I think it is me that is moving..backwards. I will draw a little cone using the time delays between the Sun and the planets out of interest.
The Sun must move towards something whilst on its journey around the arm of the gallaxy, I gather that what you say is that as it moves toward whatever that whatever also acts on the rest of the solar system.
Let me think about it I have a bank up of information to understand.
alex

[xelasnave]

I cant find the times but I think Neptune is about 4 light hours from the Sun. On my initial approach it should orbit a point where the Sun was 4 hours ago. How far does the Sun travel along (or move along its orbital path therein) the spiral arm in 4 hours? There should be that lag but then I gather there is the effect of whatever the Sun is being influenced by also acting to pull/push the planets to it, which would negate the forming of a cone shape. But whatever is acting on the Sun will act less on the planets by reason of mass differences and how that plays a part in gravitation so from that point there may be a flater cone???. I think I will go back to drinking it all seemed so much clearer then:D .
alex

[sheeny]

Ah! Alex...

Remember when Galileo proved that bodies of different mass fall at exactly the same rate of acceleration? He did that by dropping things off the leaning tower of Piza. Also Newton's law of gravitation: the force is proportional to the mass, and so is the acceleration... so all objects regardless of mass accelerate at the same rate in a uniform graviational field (which we can assume because the distance to the galaxy centre is so large).

Secondly the acceleration is towards the centre of the galaxy, which is a rightangles to the direction of motion of the solar system around the galaxy. (assuming uniform circular motion). So there is no force pulling the sun in the direction of motion - it is all purely momentum. No forces involved in that direction...

and no smoke and mirrors either!:D

Any clearer?

Al.

[xelasnave]

Thanks Al indeed it is. I have just been to a site which asked in what direction one would have to pull the string attached to a ball if one wished to have the ball orbit;) .. so your advice is timely and has been well received. Thank you.
alex

[xelasnave]

Here is a diagram of the Solar System moving from right to left of page I gather. Given our discussion and conclusion I thought it strange "they" see a bow wave how can we interpret this.. it seems that there would not be a shock wave as one would think all the surrounding space makes up the ball at the end of the string, everything should be travelling at similar speed as you observed.
I wonder if the shock wave has been detected or is it an expectation? Sorry I find it fascinating.
alex

[sheeny]

G'Day Alex,

That's all to do with the solar wind... the stream of particles emitted from the sun along with light. At the heliopause, the outward pressure of the solar wind is matched by the pressure of gas in the neighbouring space, so the solar wind basically stops.

The heliopause is egg shaped because of the motion of the sun - less distance to the heliopause looking out "the front" due to "velocity pressure". Not sure if velocity pressure is a scientific term or not, but it's a term we use in engineering to measure the velocity of a gas or air using a pitot tube. The total pressure = static pressure + velocity pressure. So in front of the solar system the total pressure is high (equals static pressure of space + velocity pressure of solar system), to the side it is moderate (total pressure = static pressure of space = static pressure of solar wind i.e. velocity pressure has not effect) and behind the solar system the total pressure is less (equals static pressure of space minus velocity pressure of solar wind - because velocity is a vector!;) ).

I wasn't aware the heliopause was egg shaped!:P :shrug:

Al.

[xelasnave]

I dont understand space time that well yet but I think its approach demands an egg shape for something moving. I dont know how many frames to say that as I dont understand how to bring time into it yet.. no worries. My point with the space craft leaving this "bubble" I made elsewhere in these forums was that they would in effect get stuck in the "stickyness" of space time... not very scientific.. when they left the bubble (on the presumption there would also be a sort of cut off point where the gravity of space would over take over the gravity of the solar system)...but after the ball on the string thinking I am not sure.
I believe gravity "pushes" and is a form of pressure somehow deriving from "star light" and all we find in it, not sure what bit yet,.. so morosophically I tend to try and see if that approach fits things I see. Runing into gases in space implies there is more there than even I thought. As you probably gathered by now law was not a good choice of careers... or maybe it was:D Thanks for taking the time maybe you should have been a teacher on second thoughts..I am not a good student.
alex