Stellar aberation, a One way measurement of c?

[Ken More]

Aberration for a star is zero only when Earth is moving in direction of that star. That of course can happen only for a star that is in ecliptic plane.

So, are you saying that declination aberration is zero only when declination (δ₀) is 0° and right ascension (α₀) is 0°? If you are saying this, then it is my openion that this disagrees with the Reduction for Annual Stellar Aberration equation: Aberration (δ - δ₀) = - x/c.cos α₀.sin δ₀ that is on page B28 in the 2010 Astronomical Almanac where x is the Earth's velocity and c is the velocity of light. When I do the math, declination aberration is zero when α₀ = 90° and δ₀ = 0° as well as when right ascension (α₀) is 0° and δ₀ = 0°. Also, since cos α₀ is always zero when α₀ = 90° then declination aberration is always zero for any declination (δ₀ from 0° to 90°) and this occurs for all stars three months from the time when α₀ = 0° when the star is in the plane that is perpendicular to the Earth's velocity vector.

If you or anyone else at Physics Forum has enough interest in this subject to get access to a copy of the 2010 Astronomical Almanac and check out my interpretation of its Reduction for Annual Stellar Aberration equation then I would be very grateful if you can tell me where I am going wrong.

 

[zonde]

So, are you saying that declination aberration is zero only when declination (δ₀) is 0° and right ascension (α₀) is 0°?

No, I was not talking about "declination aberration", I was talking about "aberration".

Astronomers probably care much more about "declination aberration" because that's much easier to measure than "right ascension aberration". So they might (I guess) shorten "declination aberration" for "aberration" but that would not be correct of course.

 

[Ken More]

No, I was not talking about "declination aberration", I was talking about "aberration".

Astronomers probably care much more about "declination aberration" because that's much easier to measure than "right ascension aberration". So they might (I guess) shorten "declination aberration" for "aberration" but that would not be correct of course.

zonde, I am very impressed! I believe you understand aberration better than anyone with whom I have ever discussed the subject. Since you are apparently an advanced stellar aberration guru, I would like to know if you think Einstein's Doppler Stellar Aberration equation in his 1905 paper "On the Electrodynamics of Moving Bodies" yields an accurate estimate of "declination aberration" or "right ascension aberration" or "intrinsic aberration" or neither. I would also like to know if you know who has an accurate model for estimating both "declination aberration" and "right ascension aberration" other than the USNO as described in the 2010 Astronomical Almanac?

 

[Ken More]

No, I was not talking about "declination aberration", I was talking about "aberration".

Astronomers probably care much more about "declination aberration" because that's much easier to measure than "right ascension aberration". So they might (I guess) shorten "declination aberration" for "aberration" but that would not be correct of course.

zonde, I will assume that you are acknowledging that astronomers can measure "right ascension aberration" as well as "declination aberration". Can they also measure "aberration" (which I will call "intrinsic aberration" henceforth)? Also, can you please tell me what kind of aberration is predicted by the Doppler Aberration equation that is in Einstein's 1905 paper "On the Electrodynamics of Moving Bodies"?

 

[PAllen]

Einstein's paper deals with total aberration, which is the combination of declination and ascension aberration (as a total displacement angle). I assume astronomers can detect both aberrations now. Having reviewed astronomic coordinates, I notice that stars at certain positions on the ecliptic will never undergo seasonal declination aberration; they will only have right ascension aberration. Stars at 90% on the ecliptic to these will have both aberrations, but the declination aberration will be smaller than the ascension aberration. Of course, for stars on the ecliptic, there will be no aberration at all twice a year.

For a star perpendicular to the ecliptic, there will always be aberration (of constant magnitude relative to position in a solar system frame), but twice a year it will include no declination aberration (it will be pure ascension aberration).

Stars in between, will have varying total aberration, and will also have no declination aberration twice a year.

Finally, I don't think any of this has to do with relativistic aberration per se. The size of the relativistic correction to classical aberration is, last I checked, undetectable for Earth's orbital speed. My guesstimate for the correction due to the difference between classical and relativistic aberration for seasonal aberration from Earth's motion would be of the order .002 arcseconds. Thus, none of this discussion has anything to do with special relativity. It only relates to the finite speed of light (Galilean versus Special relativity is not distinguished).

 

[TrickyDicky]

zonde, I will assume that you are acknowledging that astronomers can measure "right ascension aberration" as well as "declination aberration". Can they also measure "aberration" (which I will call "intrinsic aberration" henceforth)? Also, can you please tell me what kind of aberration is predicted by the Doppler Aberration equation that is in Einstein's 1905 paper "On the Electrodynamics of Moving Bodies"?

Not sure what you guys are going on about here, right ascension and declination are simply the equatorial coordinate components of the aberration, the direction northward-southward or eastward-westward of the apparent shift of the star. It looks like you are asking what the true position of a point on the Earth's sphere is, its latitude or its longitude.

EDIT: Pallen was faster to clarify it anyway.

 

[harrylin]

[..] Otherwise, even if you are right (not likely), this constitutes original research at odds with peer reviewed opinion. It is therefore not allowed to be discussed here at all - unless you provide a reference for there being a discrepancy. [..]

This is not Wikipedia and its rules don't apply - however you are completely right about the benefit of giving good references.
Regretfully I'm not familiar with such astronomical terms as "ecliptic pole", so I can't comment on the question...

 

[harrylin]

[..] I don't think any of this has to do with relativistic aberration per se. The size of the relativistic correction to classical aberration is, last I checked, undetectable for Earth's orbital speed. [..] My guesstimate for the correction due to the difference between classical and relativistic aberration for seasonal aberration from Earth's motion would be of the order .002 arcseconds. [..]

Yes that is also what I remember to have read in textbooks; last time I read about it, the difference between classical and relativistic prediction was claimed to be negligible. Thanks for confirming that.

 

[PAllen]

This is not Wikipedia and its rules don't apply - however you are completely right about the benefit of giving good references.
Regretfully I'm not familiar with such astronomical terms as "ecliptic pole", so I can't comment on the question...

There used to be an original research forum. It was discontinued. Under the guideline against 'overly speculative posts' note the following:

"It is against our Posting Guidelines to discuss, in the PF forums or in blogs, new or non-mainstream theories or ideas that have not been published in professional peer-reviewed journals or are not part of current professional mainstream scientific discussion."

and:

"Unfounded challenges of mainstream science and overt crackpottery will not be tolerated anywhere on the site."

Claiming a discrepancy between SR and observation based on own research definitely falls into those. Changing the tone (as occurred here) to 'how is the discrepancy between x and this calculation I do resolved' is perfectly ok.

 

[TrickyDicky]

I think I understood the replies to my doubts, but still I'd like to be sure, so for instance the motion of the solar system wrt the remote stars is not observed as aberration because unlike the motion of the Earth around the sun, it has a constant velocity, is that right?

 

[PAllen]

I think I understood the replies to my doubts, but still I'd like to be sure, so for instance the motion of the solar system wrt the remote stars is not observed as aberration because unlike the motion of the Earth around the sun, it has a constant velocity, is that right?

Yes. We can't detect 'absolute' aberration any more tha 'absolute rest' or 'absolute motion'. We can detect change in apparent position between two reference frames. We could detect (in principle) aberration of some distant quasar over a period of time in which the solar system's motion around the galactic center is significant.

 

[harrylin]

There used to be an original research forum. It was discontinued. Under the guideline against 'overly speculative posts' note the following:

"It is against our Posting Guidelines to discuss, in the PF forums or in blogs, new or non-mainstream theories or ideas that have not been published in professional peer-reviewed journals or are not part of current professional mainstream scientific discussion."

and:

"Unfounded challenges of mainstream science and overt crackpottery will not be tolerated anywhere on the site."

Claiming a discrepancy between SR and observation based on own research definitely falls into those. Changing the tone (as occurred here) to 'how is the discrepancy between x and this calculation I do resolved' is perfectly ok.

Yes indeed - please simply stick to the rules and avoid Wikipedia jargon.

 

[Ken More]

---Einstein's paper deals with total aberration, which is the combination of declination and ascension aberration (as a total displacement angle). I assume astronomers can detect both aberrations now. Having reviewed astronomic coordinates, I notice that stars at certain positions on the ecliptic will never undergo seasonal declination aberration; they will only have right ascension aberration. Stars at 90% on the ecliptic to these will have both aberrations, but the declination aberration will be smaller than the ascension aberration. Of course, for stars on the ecliptic, there will be no aberration at all twice a year.

For a star perpendicular to the ecliptic, there will always be aberration (of constant magnitude relative to position in a solar system frame), but twice a year it will include no declination aberration (it will be pure ascension aberration).

Stars in between, will have varying total aberration, and will also have no declination aberration twice a year.

Finally, I don't think any of this has to do with relativistic aberration per se. The size of the relativistic correction to classical aberration is, last I checked, undetectable for Earth's orbital speed. My guesstimate for the correction due to the difference between classical and relativistic aberration for seasonal aberration from Earth's motion would be of the order .002 arcseconds. Thus, none of this discussion has anything to do with special relativity. It only relates to the finite speed of light (Galilean versus Special relativity is not distinguished).

Stars in between declination θ₀ = 90° and θ₀ ≈ 0° will have varying declination aberration and varying right ascension aberration. However, stars in this range will have zero declination aberration when α₀ = 90° and 270° according to the Declination Aberration Model described in the 2010 Astronomical Almanac (AA). I agree there is no declination aberration for a star in the ecliptic plane; however, the attached "AA Declination Aberration Model for a star near the ecliptic plane" the declination aberration is zero two times a year (when α₀ = 90° and 270°). As for right ascension aberration, I can only say that the AA Right Ascension model seems to confirms that right ascension aberration is zero for a star in the ecliptic plane only when α₀ = 0.

According to Einstein’s 1905 paper: If we call the angle between the wave-normal (direction of the ray) in the moving system and the connecting line “source-observer” θ, the equation for θ assumes the form cos θ = - (cos θ₀ − v/c)/(1 − cos θ₀• (v/c)). This equation expresses the law of aberration in its most general form. If θ₀ = π/2 (i.e. if θ₀ = 90º) the equation becomes simply: cos θ = − v/c.

Therefore: When θ₀ = 90º, v = -29.783, c = 299792.458, then cos θ = -29.783/ 299792.458 = -0.005692072º = -20.491458542 arc seconds. This value agrees very closely to James Bradley’s Constant of Aberration (= -atan(v/c) = -20.491458475 arc seconds) which is the declination aberration for a star at the zenith (at θ₀ = 90º) according to Bradley’s Falling Rain Model. Bradley's model may be referred to as the "Classical" aberration model because it was the first since Bradley discovered stellar aberration in the late 1720's. Therefore, you can see that Bradley's "Classical" model and Einstein's 1905 "Relativistic" model closely agree to within 0.000001 arc seconds: That is, they both agree that the declination aberration of a zenith star (at θ₀ = 90°) has a declination aberration of -20.491458 arc seconds. I believe the Bradley model assumes a declination aberration close to 20.5 arc seconds every day of a year. Since many physicists claim that Bradley's "Classical" model and Einstein's "Relativistic" model closely agree, I must also assume that Einstein's "Relativistic" model predicts that declination aberration is about 20.5 arc seconds every day of a year.

The attached "AA Declination Aberration Model for a star at the ecliptic pole" disagrees with those who say that declination aberration is about 20.5 arc seconds every day of the year for a star at or very near an ecliptic pole. This attachment shows that declination aberration is zero when right ascension (α₀ = 90° and 270°). Also, the "AA Declination Aberration Model for declination = 75°" and "AA Declination Aberration Model for a star near the ecliptic plane" show that declination aberration is near zero when right ascension is 90° and 270°.

Finally, I believe that the AA Declination Aberration Model is the most accurate model because the Astronomical Almanac is a universally accepted authority on prediction of the precise apparent location for a star on a specific future date and time. Also, the AA Models predicted locations of important stars such as Polaris and gamma-Draconis at θ₀ = 75° (the star Bradley studied) (see attached AA Declination Aberration for Declination = 75 degrees) have been verified many times by telescopic observation.

 

[PAllen]

I don't have time to go into the details of you discussion, but I note you are repeating the same error Zonde first note, and I tried to explain in more detail:

The Bradley and Relativistic aberration formulas you quote determine total aberration not declination aberration. They say for a star at the ecliptic pole, the total aberration is constant. However, twice a year it is all right ascension aberration, twice a year it is all declination, with a mix in between.

Also note that the AA tables you quote are considered to be derived by their authors from the aberration model you dispute. They are an application of the one accepted aberration model, not an alternative model.

If you want to discuss the details of the AA conventions and calculations, you should take this over to the astronomy forum.
Further, this whole discussion of 'supposed discrepancy' has nothing to do with the topic of this thread (one way measurement of light speed using aberration).

PLEASE open a new thread in astronomy on the topic of derivation of Almanac tables from aberration formulas.

 

[Dale]

Also, as previously requested, please post a mainstream scientific reference to demonstrate that this conflict actually exists. I completely doubt it.

 

[Ken More]

I don't have time to go into the details of you discussion, but I note you are repeating the same error Zonde first note, and I tried to explain in more detail:

The Bradley and Relativistic aberration formulas you quote determine total aberration not declination aberration. They say for a star at the ecliptic pole, the total aberration is constant. However, twice a year it is all right ascension aberration, twice a year it is all declination, with a mix in between.

Also note that the AA tables you quote are considered to be derived by their authors from the aberration model you dispute. They are an application of the one accepted aberration model, not an alternative model.

If you want to discuss the details of the AA conventions and calculations, you should take this over to the astronomy forum.
Further, this whole discussion of 'supposed discrepancy' has nothing to do with the topic of this thread (one way measurement of light speed using aberration).

PLEASE open a new thread in astronomy on the topic of derivation of Almanac tables from aberration formulas.

Some do say that for a star at the ecliptic pole total aberration is constant but twice a year it is all right ascension aberration and twice a year it is all declination aberration with a mix in between. However, for an ecliptic pole star right ascension aberration is only an "apparent" spin of the pole star. This apparent spin does not change its apparent location. Therefore, we are left with a total aberration that is declination aberration only and this applies at all times during a year for an ecliptic pole star.

I have noted that the AA tables I quote are considered to be derived by their authors from the SRT relativistic aberration model. Also, they do say that their AA model equations are an application of Einstein's SRT relativistic aberration model. However, when I do the AA model math and the SRT model math Einstein's relativistic model gives very different predictions from the AA model (I am not saying that their is a discrepancy, you can do the math to see for yourself whether there is a discrepancy).

Finally, I will take your advice and open a new thread in astronomy on the topic of the aberration of ecliptic pole stars and stars near the north ecliptic pole and the south ecliptic pole. Therefore, I will hereby terminate this discussion and will not respond to any future replies to my posts on this thread.

 

[PAllen]

Some do say that for a star at the ecliptic pole total aberration is constant but twice a year it is all right ascension aberration and twice a year it is all declination aberration with a mix in between. However, for an ecliptic pole star right ascension aberration is only an "apparent" spin of the pole star. This apparent spin does not change its apparent location. Therefore, we are left with a total aberration that is declination aberration only and this applies at all times during a year for an ecliptic pole star.

This is incorrect. The ecliptic pole is not the celestial pole. It is only the north polar star for which right ascension is undefined. The ecliptic pole will differ in declination from the polar star by the tilt of Earth's axis.

I have noted that the AA tables I quote are considered to be derived by their authors from the SRT relativistic aberration model. Also, they do say that their AA model equations are an application of Einstein's SRT relativistic aberration model. However, when I do the AA model math and the SRT model math Einstein's relativistic model gives very different predictions from the AA model (I am not saying that their is a discrepancy, you can do the math to see for yourself whether there is a discrepancy).

All this shows is that they know what they are doing and you don't. Since this is purely a question of the details of applying aberration in a particular astronomic coordinate system, the appropriate forum to clarify the calculations and find your error is the astronomy forum.

Finally, I will take your advice and open a new thread in astronomy on the topic of the aberration of ecliptic pole stars and stars near the north ecliptic pole and the south ecliptic pole. Therefore, I will hereby terminate this discussion and will not respond to any future replies to my posts on this thread.

Fine.

 

[ghwellsjr]

Now that the hijacking is over, can any of you experts on aberration please answer the OP's question?

 

[harrylin]

Now that the hijacking is over, can any of you experts on aberration please answer the OP's question?

Oops you're right. OK then, let's make a start. I think that it has already been clarified that aberration is caused by the velocity difference due to the Earth's orbit. The Earth's orbital speed is simply its speed relative to the Sun; and the Sun does not designate an absolute reference frame. Instead we could for example choose the combined speed of Earth + Sun through the Milky way. That would yield a very different one-way speed of light if we use the same t.

It always boils down to the same thing: if we choose a certain reference system as "rest" frame, then we will measure the speed of light relative to it as c, but else we won't. And then it depends on what one means with "one way measurement of c".

 

[PAllen]

Oops you're right. OK then, let's make a start. I think that it has already been clarified that aberration is caused by the velocity difference due to the Earth's orbit. The Earth's orbital speed is simply its speed relative to the Sun; and the Sun does not designate an absolute reference frame. Instead we could for example choose the combined speed of Earth + Sun through the Milky way. That would yield a very different one-way speed of light if we use the same t.

I don't think this is true. I think a very careful analysis (which I have not done) would show that this case is equivalent to slow clock transport - the one way speed would always be measured as c, but this measurement would be an artifact in the theories that have underlying anisotropy of one way c in most frames.

 

[harrylin]

I don't think this is true. I think a very careful analysis (which I have not done) would show that this case is equivalent to slow clock transport - the one way speed would always be measured as c, but this measurement would be an artifact in the theories that have underlying anisotropy of one way c in most frames.

I basically agree with that (except for a subtle difference which has been discussed); thus I don't know what you think is not true...

 

[PAllen]

I basically agree with that (except for a subtle difference which has been discussed); thus I don't know what you think is not true...

I thought you were saying you could measure something different from half the two way speed. If that's not what you meant, then I misunderstood.

 

[harrylin]

I thought you were saying you could measure something different from half the two way speed. If that's not what you meant, then I misunderstood.

Oh sure that is what I meant, but likely not in the way that you understood it, since we seem to agree on all essential points.

I tried to make the OP realize (in a continuation in part of my post #15) that if we assign a different velocity to the Earth by accounting for the motion of the Sun (as we may) while keeping the same time t (which he/she seems to take for granted), then necessarily v/t differs from what the OP calculated. I thus stressed a mathematical fact to the OP in the hope to bring home that although one might call his/her method a "one way measurement of c", it remains a very "relative" measurement.

Thus -again- it depends on what Tracer exactly means with "one way measurement of c". I think that it undeniably a method to determine the constant c with a certain precision. Next it may deteriorate in another argument about words, in which I won't participate.

 

[PAllen]

Oh sure that is what I meant, but likely not in the way that you understood it, since we seem to agree on all essential points.

I tried to make the OP realize (in a continuation in part of my post #15) that if we assign a different velocity to the Earth by accounting for the motion of the Sun (as we may) while keeping the same time t (which he/she seems to take for granted), then necessarily v/t differs from what the OP calculated. I thus stressed a mathematical fact to the OP in the hope to bring home that although one might call his/her method a "one way measurement of c", it remains a very "relative" measurement.

Thus -again- it depends on what Tracer exactly means with "one way measurement of c". I think that it undeniably a method to determine the constant c with a certain precision. Next it may deteriorate in another argument about words, in which I won't participate.

Ah, but what one actually measures is difference in angle between frame E1 (earth in January, for example), and frame E2 (earth in June). This difference in angle will be dependent only on the relative velocity of E1 and E2, irrespective of whether one treats E2 relative to E1, both relative to a Solar frame, or both relative to a galactic frame.

Note that if, in addition to measuring change, you choose to express the result as deviation from an average position, the length of averaging selects which inertial frame you are implicitly choosing for your coordinates: a day (earth centered frame; rotation aberration, which exists but not discussed much in this thread), a year (solar frame), the solar orbital period in milkyway (galactic frame).

As for time, you only (directly) need one clock (which you must assume measures time uniformly). You also need to know the relative velocity between E1 and E2, which does raise tricky issues if you don't want to be circular (as discussed earlier in this thread).

 

[PAllen]

I found reference to the statement that pages 94-5 of the following:

Special Relativity and Its Experimental Foundations (Advanced Series in Theoretical Physical Science) [Hardcover]
Yuan-Chung Chang (Author), Yuan-Zhong Zhang (Author)

discuss the details of how stellar aberration gives no more information about one way light speed than other attempts of this type (e.g. slow clock transport).

Unfortunately, I can find no 'search in book' type feature to find this online, and this book is apparently not easy to find.

 

[harrylin]

Ah, but what one actually measures is difference in angle between frame E1 (earth in January, for example), and frame E2 (earth in June). This difference in angle will be dependent only on the relative velocity of E1 and E2, irrespective of whether one treats E2 relative to E1, both relative to a Solar frame, or both relative to a galactic frame.

Note that if, in addition to measuring change, you choose to express the result as deviation from an average position, the length of averaging selects which inertial frame you are implicitly choosing for your coordinates: a day (earth centered frame; rotation aberration, which exists but not discussed much in this thread), a year (solar frame), the solar orbital period in milkyway (galactic frame).

As for time, you only (directly) need one clock (which you must assume measures time uniformly). You also need to know the relative velocity between E1 and E2, which does raise tricky issues if you don't want to be circular (as discussed earlier in this thread).

Yes, thanks for the elaboration.

Note that we don't necessarily assume that a clock measures time uniformly; however that assumption is quite OK for clocks in orbit around the Sun if we use the solar frame; and I don't think that such calculations and measurements are based on atomic clocks anyway.

 

[Tracer]

Originally Posted by PAllen
Ah, but what one actually measures is difference in angle between frame E1 (earth in January, for example), and frame E2 (earth in June). This difference in angle will be dependent only on the relative velocity of E1 and E2, irrespective of whether one treats E2 relative to E1, both relative to a Solar frame, or both relative to a galactic frame.

Yes, thanks for the elaboration.

Note that we don't necessarily assume that a clock measures time uniformly; however that assumption is quite OK for clocks in orbit around the Sun if we use the solar frame; and I don't think that such calculations and measurements are based on atomic clocks anyway.

I tracer am a he. Thanks to all who have responded to my question. Your posts and references have been very enlightening on the subject of stellar aberration. Yes, my question is does stellar aberration offer a means to measure the speed of light in just one direction? I gather from your responses that the answer is yes but that the Earth's orbital velocity and the length of an AU would be difficult to measure noncircularly, accurately and realistically.

Therefore, somewhere in this thread I proposed that the speed of light in opposing directions could be determined without involving the length of an AU or the Earth's orbital velocity or a wait of six months between measurements. If a device much more simple than a massive telescope is used which can be quickly reversed 180° easily and accurately to view a reflected image of a star, then if the angle of aberration is the same for reversed positions of the viewing device, then wouldn't the speed of light be the same for passage through the device in opposite directions? If this is true then it should be correct to assume that all measurements that show the two way measurements of the average speed of light to be c are actually the average of two one way passes of light at c in both directions.

 

[PAllen]

Originally Posted by PAllen
Ah, but what one actually measures is difference in angle between frame E1 (earth in January, for example), and frame E2 (earth in June). This difference in angle will be dependent only on the relative velocity of E1 and E2, irrespective of whether one treats E2 relative to E1, both relative to a Solar frame, or both relative to a galactic frame.



I tracer am a he. Thanks to all who have responded to my question. Your posts and references have been very enlightening on the subject of stellar aberration. Yes, my question is does stellar aberration offer a means to measure the speed of light in just one direction? I gather from your responses that the answer is yes but that the Earth's orbital velocity and the length of an AU would be difficult to measure noncircularly, accurately and realistically.

Therefore, somewhere in this thread I proposed that the speed of light in opposing directions could be determined without involving the length of an AU or the Earth's orbital velocity or a wait of six months between measurements. If a device much more simple than a massive telescope is used which can be quickly reversed 180° easily and accurately to view a reflected image of a star, then if the angle of aberration is the same for reversed positions of the viewing device, then wouldn't the speed of light be the same for passage through the device in opposite directions? If this is true then it should be correct to assume that all measurements that show the two way measurements of the average speed of light to be c are actually the average of two one way passes of light at c in both directions.

You can't measure aberration in one frame, at all, period. Aberration relative to what? You have to involve two frames with known relative velocity, which has been determined in some non-circular way. I think this can be done, and the result is similar in character to slow clock transport measurements: the result is not known a priori (unlike with light based synchronization; so it is a real experiment), but as long as two way light speed isotropy holds, and the prinicple of relativity holds, the measurement will yield c even if there is underlying anisotropy of one way lightspeed (in such a way as to preserve two way isotropy and the principle of relativity). One sense in which it is a real measurement is that if you detected anisotropy of c, this would mean that SR (and all equivalent theories) are false; and then it could be giving unambiguous information about one way light speed.

 

[Tracer]

You can't measure aberration in one frame, at all, period. Aberration relative to what? You have to involve two frames with known relative velocity, which has been determined in some non-circular way. I think this can be done, and the result is similar in character to slow clock transport measurements: the result is not known a priori (unlike with light based synchronization; so it is a real experiment), but as long as two way light speed isotropy holds, and the prinicple of relativity holds, the measurement will yield c even if there is underlying anisotropy of one way lightspeed (in such a way as to preserve two way isotropy and the principle of relativity). One sense in which it is a real measurement is that if you detected anisotropy of c, this would mean that SR (and all equivalent theories) are false; and then it could be giving unambiguous information about one way light speed.

I respectfully disagree with you. I would like to provide additional details of the experiment which was proposed. However, If doing so will cause me to be locked out or banned I will just shut up and go away. What I have proposed is not speculation, a new theory, or an attempt to disprove anything. I am only proposing a test of which I think you misunderstood my description.

 

[harrylin]

I respectfully disagree with you. I would like to provide additional details of the experiment which was proposed. However, If doing so will cause me to be locked out or banned I will just shut up and go away. What I have proposed is not speculation, a new theory, or an attempt to disprove anything. I am only proposing a test of which I think you misunderstood my description.

PAllen is certainly right but it's unlikely that you will be banned for describing in detail the rather standard test which we probably already discussed here and understood.
However, you now clarified that you were not looking to establish the constant "c" with a certain precision by means of a one-way light signal; instead you propose that method, as some already suspected, as a means to determine the physical speed of light in one direction - correct? If so, in your more detailed explanation of what you have in mind, please include an reply to my assertion in post #49.