Aberration of starlight, was discovered and measured by Bradley at the end of '700.
Bradely detected a constant angle of tilting of the telescope 20", the tangent of it corresponds to v/c (he was aware of the estimation of the speed of light made by Romer) with v = 30km/s is the speed of Earth around Sun.
Aberration is due to a change of position of the observer in regard to light rays while they cross the telescope. Because the telescope moves a distance vh/c during the time it takes light to travel down the tube, the tube must be tilted in the direction of motion for the light to move along the optical axis of the tube.
An indirect measurement of Earth's speed rotation was found by Bradley.
Bessel in 1838 managed to implement the stellar parallax and needed to deal with aberration. He excluded that the motion of the stars could make any difference, due to their distance hence corroborating Bradely's explanation of the phenomenon.
In '800 when the Luminiferous Aether was in vogue, many including Stokes tried to provide an explanation with aether dragged but it was not found compatible.
Einsteins in 1905 provided an explanation of it with the Lorentz Transformations. The angle as v/c comes from a first approximation of the formula of aberration in SR, where v is the speed of the observer in the reference frame of the source.
This demonstration considers also the fact that since stars are quite far away so rays come parallell as if they come from infinite distance.
There is also an aberration due to rotation of Earth, but in this case it is quite small since the speed of rotation of earth is lower than .5 km/s on its surface hence the value of the aberration due to it is about 60 times smaller, depending also on the position on earth of the telescope.
Only in 1925 Hubble discovered that we are part of a galaxy and after that it was clear that the relative speed of earth and stars can reach 400 km/s.
So why stellar aberration should depend only on the speed of the earth around the Sun (and around itself) but is virtually independent of the speed of Sun in the galaxy?
The satisfactory answer given by some partecipants seems to be:
Bradley made a certain observation with a certain inclination of the telescope on Earth's orbit such that he would only spot close enough stars which are virtually in the same restframe as the solar system.
Dear Stefano Quattrini , unfortunately, I saw your addition to the message too late here https://www.researchgate.net/post/Why_is_a_debate_about_twins_paradox_so_bad/32
So I’m only duplicating the last paragraph of my answer:
= = =
Assuming that you forgive me such an extended «blah-blah-blah», we can return to your message. Let us compare our views on the phenomenon of aberration (as a property of electromagnetic radiation to deviate from linear propagation). Do you agree with the following statements:
1. Aberration occurs only if accompanied by a change in the light velocity vector module?
2. The modification of the said module is not always accompanied by the phenomenon of aberration?
Honestly, the meaning of the second paragraph I did not understand (perhaps because I do not know what the letters vx/c2 mean).
With kind regards
P.S. You should bear in mind in this case that I have never been interested in the phenomenon of aberration before; therefore you should not consider my opinion in your research.
Dear Sergey Sheludko ,
to my understanding the actual effect of 20" of tilting, which corresponds to v/c, gives v=30 km/s as a modulus of the vector in the SUN centered frame.
It has nothing to do to the change of the vector module of the beams, but with a non zero lateral speed.
apparently no, considering that sun goes at 300 km/s in the galaxy. If you consider the speed of Earth in the center of the Galaxy instead of the SUN centered frame, the aberration relevant to that is virtually not detectable.
the Lorentz Transformation at the first-order approximation is
t'=t - vx/c2 , that term in the transformations is responsible of the strange behaviour, it bends light rays..
the only solution which I see is that light rays do not travel in the reference frame of the source but in a local preferred frame. After crossing sidereal spaces the local preferred frame is the "gravitational field" of the SUN.
Dear Georges Sardin ,
it would be nice your participation to this thread.
Thank you
Dear Stefano Quattrini ,
>> to my understanding the actual effect of 20" of tilting which corresponds to v/c gives v=30 km/s as a modulus of the vector in the SUN centered frame//
Excellent, I can only notice that as a result of your research you will be able to understand the difference between «Lorentz» and «No-lorentz».
It took me an hour to come to the same conclusion I came to, not interested in aberration. I assure you that there is already sufficient information at your disposal to make your own choice between the two solutions.
Physicists use the concepts of «object» or «system of objects»; the concept of «frame» belongs to relativists :))
>> apparently no, considering that sun goes at 300 km/s in the galaxy //
Your remark has nothing to do with the essence of the matter; note that any physical measurement is comparing of some values. To measure secular aberration, you must wait until you are on the opposite side of our galaxy :))
>> the Lorentz Transformation at the first order approximation … it bends light rays..//
Transformation of what and why? I do not like approximations when it is necessary to find an accurate solution; measurements are always made with errors/approximations.
You didn’t want to tell me exactly where Lorentz’s bending take place :))
With kind regards
The velocity of our solar system is about 370 km/s in relation to the rest frame of the electromagnetic field. The measurement is done with the help of the CMBR dipole and confirmed in Juli 2022 (Jeremy Darling in “The Universe is Brighter in the Direction of Our Motion: Galaxy Counts and Fluxes are Consistent with the CMBR Dipole” (https://iopscience.iop.org/article/10.3847/2041-8213/ac6f08). The proposed velocity of the sun around the Milky Way – with the centre of the Milky Way as point of reference – is about 230 km/s.
This video shows the motion of the earth around the sun (https://www.youtube.com/watch?v=0D5OzdCBlE0&t=48s) and there is also a new video (Februari 2023) about the motion of the sun around the centre of the Milky Way (https://www.youtube.com/watch?v=1lPJ5SX5p08). It is a bit a surprise because the video also describes the motion in relation to the CMBR dipole (368 km/s).
But if there is a rest frame in the universe, there is a resultant motion of the quanta transfer around celestial bodies within the structure of the electromagnetic field in vacuum space. The cause behind this resultant motion is the gravitational field of celestial bodies (Newtonian gravity as a vector force from vacuum space around). The resultant motion of the quanta transfer influences the observation of the position of stars in the night sky. So I am quite sure that the aberration of starlight has another origin than the text books describe.
With kind regards, Sydney
Dear Preston Guynn ,
thanks a lot for the link to the paper you posted, I knew it already, adds not much in what has been already written.
Dear Sergey Sheludko ,
YES
yes, the effect cannot depend only on the motion of the observer in the "rest frame" of the Star, there is a quite peculiar mechanism which allows that the speed entering the formulas refers only to 30KM/s for its 99% , the revolution speed of earth around the SUN.
so to measure annual aberration I should wait one year, but we are not talking about that, we are talking about something in real time.. it is the variation of the position of the observer in regards to a source of light.
I stay very firm on the fact that Light is detected tilted due to the rate of change of position of the observer. It is to be discarded that light in general, transversally to its direction of emission, takes the inertia of the source.
Dear Stefano Quattrini ,
As you may know, there is a problem in special relativity in regards to aberration. It is pointed out by Wolfgang Engelhardt here (please see Fig. 3):
http://redshift.vif.com/JournalFiles/V10NO4PDF/V10N4ENG.pdf
I see no problem in Bradley's formulation of the aberration.
Sorry, I forgot something in my previous comment.
The diagram above shows the mean velocity and mean distance of the planets in our solar system.
But the distinct orbits and the angle of rotation around the sun differ a lot. But amazingly there is a direct mathematical relation between all the planets around the sun. Already discovered by Kepler.
But if I calculate the influence of the force of gravitation on the freedom of quanta transfer in every point within the structure of the electromagnetic field in vacuum space (within the solar system) I get nearly the same diagram.
So it is not only the aberration of the light of distant stars, it is about the physics behind accretion disks and Black hole jets too. Actually, it is about Christiaan Huygens centrifugal and centripetal force “in vacuum space”, used by Newton to link the Earth' gravitation to the orbits of the planets around the sun.
With kind regards, Sydney
Dear Stefano Quattrini
An interesting question. Here is my layman observation.
Stars we generally observe are within the Milky Way. I'm not talking high-power scopes that look into other galaxies.
Because of the 'mostly flat' rotation curve (*cough - due to dark matter) of our spiral galaxy, we could say that all our nearby stars are 'standing still' relative to our sun, and because our sun is in the same rotation curve.
Only for the earth orbiting the sun is another v component added, so we are moving relative to the sun AND all the other stars, which causes abberation of observing stars IN the Milky Way AND in nearby areas.
It would be totally different if we could see a star 54000 lightyears away at the 'other side' of the milky way, which would be in opposite direction with abberation angle of sun+earth+star velocity at the tangent.
Kind Regards
EDIT, because I could not find how to reply again
Dear Francois Zinserling
the relative speed of some is presumably close to 0 (ALPHA CENTAURI is just some light years away). Concerning other stars which are located on the opposite side of the center relative to Earth, the relative speed can even reach 400km/s...
the relative speed can be even 400km/s...
Are you saying the abberation for these are the same? As if the difference was only 30km/s?
I would not have thought it could be, but if it is so then I see your concern.
Dear Francois Zinserling ,
Yes, the aberration angle of starlight is about theta = 20" , measured by Bradely about 3 centuries ago, has the same value irrespective of the stars.
The only speed which comes out of tan (theta) = v/c is always very close to the one of the sun around earth : 30 km/s.
By the way, why that sums up or subtract to the aberration due to earth rotation speed (0.4 km/s) which is very small, and not add or subtract the relative speed of the sun in the galaxy?
I think it unlikely that Bradley would have seen stars in the opposite side of the disk. Most stars we see in the night sky are 'nearby'
I have another point to make though, or a question rather since the answer eludes me, but may add to your topic.
We all know Einstein's thought experiment where the light bounces off a mirror. Picture in your mind a torch reflecting from a mirror straight back at you. Your torch is pointed straight 'NORTH'. You are moving relative to a stationary observer who sees everything moving and the light path for him looks like a 'triangle'.
My question is - how does the observer see the light coming out of the torch? Is the torch itself now twisted at an angle that you observe? I would think not. Which means you see the torch pointing 'north' but the light is pointing 'northeast'. (exaggerated)
This shows that light leaves the source with the momentum vector of the source. Yes, speed is only 'c' but direction is part of the vector.
Am I making sense?
Dear Francois Zinserling ,
with telescopes we can see now far away nebulas travelling at considerable relative speed but the aberration is always the same as the one measured by Bradley at least with a very good approximation.
I do not question Einstein's derivation under the hypotheses he made at that time: still and very distant stars. But I question it under the evidence that most stars are only apparently still because they are far.
So if it is as you say, then actually one should see different aberration values from different stars, since light is seen to take the inertia of the source in the transverse direction to its motion (this is by the way what Lorentz Transformation say).
it is the case to refer to other "relatively" recent papers referring to aberration to see how certain aspects have not been taken into consideration.
Article Why the Bradley aberration cannot be used to measure absolut...
I agree with that paper: it is certainly incorrect a connection between aberration and absolute motion, on the contrary aberration gives evidence only of the motion of Earth around Sun.
On the other hand, the explanation of Special relativit, so far the only one widely accepted, can hold only the hypothesis that the stars (besides the fact that they are quite far) define a rest frame (Newtonian fix stars).
Stefano Quattrini
Compare how much the direction of travel changes from year to year. Around the sun, the direction of travel changes significantly in a half of a year. But around the galaxy, the direction of travel changes very little. Without a significant change in the direction of travel, there is no measurable aberration.
Centripital Acceleration = v²/r = (2πR/T)²/R = 4π²R/T²
For earth’s orbit around the sun,
- R=1.58E-5 ly
- T= 1 year
- a=6.23E-4 ly/y²
- x (9.46E12 km/ly)(1y/31.6E6 s)
- = 187 km/s per year
For the sun’s orbit around the milky way
- R=100,000 ly
- T= 200,000,000 y
- a=9.87E-11 ly/y²
- x(9.46E12 km/ly)(1y/31.6E6 s)
- = 2.95E-5 km/s per year = 2.95 cm/s per year
Jonathan Doolin ,
to my understanding, the approximate 20'' aberration angle measured, has nothing to do with the "direction of travel" or the centripetal acceleration.
That feature has never been mentioned in any analysis to my knowledge.
Aberration on the contrary has to do with the speed at which a telescope crosses the "parallel" rays, it has to do with changing its position as a function of time, not it in general its direction.
So you would mean that with a very distant source of light and one observer going in a straight line with a relative speed in regard to the source, no aberration should be detected...
Although there should be also such effect of change direction, the centripetal acceleration of earth around Sun is in any case negligible in comparison to the one relevant to the rotation of earth.
On the other hand the contribution to the detected aberration due to rotation of earth, although present, is an order of magnitude smaller than the contribution of the aberration of starlight due to the motion of earth around the SUN.
Dear Stefano Quattrini ,
>> … which allows that the speed entering the formulas refers only to …//
I’ve already explained too much to you. And can you explain why you are so careful to avoid writing down the very formula that is clogged all over the Internet? My clue is that physicists and relativists use two fundamentally different formulas, which for 30 km/s give almost the same result.
Yes, I found that elsewhere you had deviated from your habit:
>>The aberration of starlight gives about such speed having approximately always the same angle tau= v/c.// Curiously, this angle you will measure in radians, degrees, degrees of Fahrenheit, …?
Does this mean that only I know the difference? No!!! As soon as I depicted the graphically physical formula, my discussion topic was immediately closed; neither I nor my opponent could add any more file, and I had to answer it elsewhere (namely here https://www.researchgate.net/post/Speed_of_light_independent_of_the_speed_of_the_source_or_constant_for_all_observers/16 ).
Look how cute the rationale I added with my own hands looked:
>>P.S. You can learn about copyright and ResearchGate here, and find links to specific publishers' policies here.
Sorry, you can't add your file "3 body Du.jpg". The publisher, name unknown, has required us to block public uploads of this file. Learn more.
Please remove the file. You can try adding a different file. :(( //
Do you have any idea that I try to add my own files exclusively?
Do you realize that if I try to explain anything else, your topic could be compromised?
Anyway, I wish you victory in Star Wars.
Dear Sergey Sheludko ,
I don't understand what you are referring to..
Dear Stefano Quattrini , nevertheless, I wish you success in your research.
With kind regards
Dear Preston Guynn ,
Do you want to say again that the aberration of 20" is due to the change of direction of the observer?
Is it not enough the example of the variation of direction of an observer which sits on the surface of Earth? That variation in direction per unit time is much larger than the variation of speed of earth around the Sun, but the relevant aberration has very little contribution in the aberration angle of 20". That little contribution it is again proportional to the .4 km/s instantaneous tangential speed order of magnitudes smaller than 30 km/s.
SUN centered frame of reference does not necessarily have to match the center of mass of the solar system. What is important is the fact that they translate together.
speed of earth referred to the center of the galaxy.
That speed does not enter in the computations otherwise the aberration would be much larger, but as a matter of fact it should...
That has to do with the variation of the contribution of aberration which is already negligible: from the referred paper "The circular motion of the solar system barycenter around the Galactic center causes a change in aberration, which in the case of geodetic VLBI observing is over time scales of several decades"
But the fact the current value of the aberration is negligible, is not justified at all by the fact that the centripetal acceleration is very low, as I already mentioned.
Stefano Quattrini
You have to consider two things. One is how fast the aberration accumulates, and the other is the maximum aberration observable. In the case of stellar aberration from the rotation and revolution of earth, the maximum aberration dominates, because we can easily wait half a day or a half a year. But in the case of revolution around the galaxy, the accumulation term dominates, because we are not waiting 100 million years to traverse the galaxy.
Centripital Acceleration = v²/r = (2πR/T)²/R = 4π²R/T²
For earth’s orbit around the sun,
- R=1.58E-5 ly
- T= 1 year
- a=6.23E-4 ly/y² x (9.46E12 km/ly)(1y/31.6E6 s)
- = 187 km/s per year
- = 93.5 km/s in half a year
For the sun’s orbit around the milky way
- R=100,000 ly
- T= 200,000,000 y
- a=9.87E-11 ly/y² (9.46E12 km/ly)(1y/31.6E6 s)
- = 2.95E-5 km/s per year = 2.95 cm/s per year
- = 2950 km/s in 100 million years
For the earth’s rotation around its axis
- R=6378 km
- T=1/365 = .00274 y
- a = 10.7E9 km/y^2 = 338 km/s per year
- = 0.463 km/s in half a day (sundown to sunrise)
Dear Stefano Quattrini,
Thank you for inviting me to participate in the debate. However, in view of my advanced age and a demanding health state, I do not participate anymore to debates. I am just pointing out two past papers.
I think that to widely understand stellar aberration one should also consider the fact that local light does not undergo aberration while non-local light does, such that from stars. The cause is pondered in the following paper:
A dual set-up based on Bradley's aberration of light, using simultaneously stellar and local light sources Article A dual set-up based on Bradley's aberration of light, using ...
The speed-induced deflection of light from local source is further addressed and pictured in the following animation:
Animation of Michelson experimentPresentation AnimationMichelsonexperiment
Diverse other issues are available in My Open BOOK on PhysicsCover Page My Open BOOK on Physics
Best regards.
Dear Preston Guynn ,
centripetal acceleration was mentioned for the first time in the thread by Jonathan Doolin and you made referece to what he wrote. I just reported what was written.
After noticing such a physical "aberration", my aim was to kill for good any hypothesis of contribution of variation of direction of speed in Bradley's detected aberration of 20" , but maybe I did not understand well.
The contributions shown by Doolin are relevant to the secular change of the angle of aberration due to position of solar system in the Galaxy, but this is off topic, what has been asked is the explanation of what contributes and does not contribute to the value of 20" and why.
Bradley's aberration angle of 20'' was found in one peculiar condition: orientation of the telescope with a reasonable approximation normal to the earth's orbital plane.
you are dealing with superior order approximations which are not relevant in this discussion, I think you manage to understand it.
Dear Preston Guynn ,
thanks a lot for your time indeed and I apologize for appearing in contradiction.
Dear Francois Zinserling ,
you were quite likely right.... it is not irrespective of the position of the star observed...
Dear Stefano Quattrini ,
Like you, I am also an explorer of knowledge. I was not commenting from a state of 'knowing' but just according to my understanding.
To the more learned ones in the group, sometimes our questions may seem repetitive and even offensive while we seek understanding. Offense is never intended.
For me the take-away from this discussion (and I thank you for opening it)
- Abberation is because of the planet movement, and the only reason Bradley found it out because there was a 'left and right' (apologies for the poor analogy) movement around the sun, which caused angle of abberation to change.
- Galactic abberation must be much bigger, but we don't know that we are looking at a wrong angle, because we are only going in 1 direction in the galaxy so the error is consistent. I think this is what Jonathan Doolin was trying to show, although I also did not get his point at first. Now it makes a lot more sense.
- I still think Bradley would have only seen local stars (with technology he had) so to him the stars 'stood still' and the earth moved. At least he was not the one who thought the earth stood still and everything else moved :)
Regards
Dear Francois Zinserling ,
yes, Bradley by pointing his telescope in the direction normal to the earth orbital plane as anybody else though, detected light from close stars only, also due to the limited power of the tool.
A normal line to Earth's orbital plane (tilted of 60deg with the galaxy plane) does not cross the galaxy enough to catch stars whose relative motion with Solar system is fast, hence only the stars close to Earth are seen at that angle. As you said, these stars are stationary with the SUN with a good approximation.
"So why stellar aberration should depend only on the speed of the earth around the Sun (and around itself) but is virtually independent of the speed of Sun in the galaxy?"
To simplify what Sergey Sheludko and Jonathan Doolin has explained - in order to measure annual aberration (due to the Earth's orbital motion) you need to wait half a year (or so) to have the Earth moving in a different direction, so you can measure the change in the positions of stars. In order to measure the galactic aberration (due to the Sun's orbital motion around the galactic centre) you need to wait half a galactic year, so around 100 million years. This is not practical, so if you wait just a couple of years the direction of motion of the Sun is almost the same, so the change in the positions of stars due to this effect is negligible.
On page 1 you find the Kepler diagram of the mean velocity/mean distance of the planets of our solar system. The diagram shows the influence of the gravitational force of the sun in relation to the resultant motion of the quanta transfer everywhere in vacuum space.
But every planet in our solar system has its own “Kepler diagram” too. That means that the mean distance and mean velocity of the (small) moons around a planet will show the same exponential curve.
Therefore the influence of the Milky Way on the stellar aberration isn’t dominant because most of the stars of the Milky Way – and the energy transfer in interstellar space – show the same velocity (the nearly flat diagram of the rotational velocity of all the stars in the Milky Way that is thought to be caused by the existence of Dark Matter).
It is more interesting to question the influence of the resultant motion of quanta transfer (in the past hypothesized as “aether drag” by Fresnel, Stokes and Lorenz) of all the energy transfer in vacuum space under influence of the force of gravitation. Thus there is an aberration effect in vacuum space “everywhere” in the solar system by the existence of the sun and there is the same effect in vacuum space around every planet, inclusive the Earth. Etc., etc.
In general "our" stellar aberration is a composition of:
All these different types of stellar aberration are measured so there is no doubt about their existence.
With kind regards, Sydney
The distance of the stars is irrelevant to the phenomenon of aberration (as opposed to parallax, which depends only on their distance). It is a localized phenomenon, caused only by the motion of the observer (relative to the speed of light), and has nothing to do with the distance of the stars, so the explanations suggesting that stellar distances are of any importance are incorrect.
I might note that although most of those who answered this are obviously familiar with stellar aberration, in case there is anyone who wants a simple explanation (e.g., for friends or students who aren't familiar with astronomy), there is one posted on my astronomy website at http://cseligman.com/text/history/bradley.htm (*One nonexistent diagram states has a caption stating that the diagram will be posted soon, but I forgot what I was going to use the diagram for, so it is only there in the hope that at some time I will remember what it was, and post the diagram, after all*)
yes you are right, what counts is the relative speed.
The point is that our distance with the stars in the galaxy is correlated with the relative speed to us. The closer, the most visible the slowest virtually still.
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