On 10 May 2007 04:09:06 -0700, George Dishman wrote:

On 10 May, 01:30, HW@....(Henri Wilson) wrote:
On 8 May 2007 23:58:13 -0700, George Dishman wrote:
On 9 May, 00:41, HW@....(Henri Wilson) wrote:

You have been claiming that the speed didn't appear in
the equation and that wavelength couldn't change. One
or the other is wrong. You also claimed the formula
used frequency instead of wavelength but that too isn't
true. Naturally you can replace the wavelength by speed
over frequency but that just reintroduces speed in the
equation.

Desperate again George?

I'm having to teach you basic algebra yet again Henry.

Lambda_i is absolute and all we need.

Lambda_r doesn't enter into this.

Lambda_i isn't enough, if you want to use it you need
to know v and u as well but the grating doesn't measure
them. Remember all we know is the angle phi so you
can turn the second version round to get

Lambda_r = D * sin(phi)

but that's as far as you go. Your first equation isn't
usable because v and u aren't known so in BaTh a
grating doesn't measure Lambda_i, only Lambda_r.

George, Lambda_i is known. It is absolute and universal for a particular
spectral line.

No it isn't, you are forgetting that it gets changed by speed
equalisation. If the wavelength didn't change, there would
be no Doppler shift whatsoever.

That's another issue, leave it out for now.

It is fundamental, the purpose of a grating is to
measure an unknown wavelength.

No it isn't. It uses the angle of diffraction to measure the velocity of the
source, knowing the true absolute wavelength.



The difference between the measured angle and the expected one is a measure of
c+u/c+v
(Can we assume u is zero?).

No, you can't assume that but even if you did you
don't know v or lamda_i, the whole point of using a
grating is to _measure_ something you don't know.

Don't try to wriggle out with this distraction George.

It is not a distraction, a grating is a measuring instrument
and what it measures in BaTh is the _reflected_ wavelength,
nothing else. Other parameters my be inferred using
assumptions but they are not measured.

explained in the other message.

Conventionally v=0, u=0 and lambda_r = lambda_i
but in BaTh none of those are known. The
measurement of phi tells you lambda_r only.

George, the wavelength of, say, Halpha is absolute and universal.

You forget the Doppler shift due to proper motion of the
source. The grating has no idea the light is hydrogen
alpha, the fact is that the angle of deflection depends
_only_ on the reflected wavelength.

George the grating hasn't but the observer should know how to recognize certain
lines..

If you are using that in your grating, even if it HAS changed during travel,
the assumption that it hasn't will still allow the observed diffraction angle
to be used to calculate initial c+v.

It is an assumption Henry, the fact remains that what a
grating measures in BaTh is the reflected wavelength.

No George. Its diffraction angles are sensitive to wavelength but its main
function (we're talking astronomy remember) is to determine source speed.

Certainly it CAN be and has widely been used to measure wavelength if the
source is at rest wrt the grating.

snip repetition

...
George, if you want to measure lambda_r, you will have to put another grating
in the diffracted beam.

No, the equation for a single grating in BaTh, what you
called the "grating equation" tells you Lambda_r, not
Lambda_i.

please read again george.

It still says the same thing and it is still wrong, for a single
grating, the angle of deflection depends on the reflected
wavelength:

You're still bogged down in the constant c model.

Lambda_r = D * sin(phi) / N

Anything beyond that requires assumptions and calculations.

George, I'm talking BaTh not fairyland physics.



SR does not predict that the HST should detect variations in diffraction angle
due to its own orbit speeds.

Yes it does, it produces the same equation.

Light sped is not in the SR equation.

Lambda_i is known.

No, or there would be no point in measuring it.

It isn't measured. It is known and used to calculate relative source speeds.

The purpose of a grating is to make a measurement, that
is what the 'grating equation' does for you. The thing that
is measured is the reflected wavelength. Note that is
based on you diagram and I have a minor reservation
about it but you need to learn the basic principle before
we look in more detail.

George, gratings are used to determine wavelengths from sources at rest wrt the
grating.
This whole discussion is about the relatively moving situation.
So don't try to distract me with irrelevancies....

Don't be stupid, both theories give the same equation.
However, in BaTh a grating cannot measure what you
call the 'absolute wavelength', only the reflected
wavelength. That's a limitation which suggests you
would need other instruments to find v and u.

They don't give the same equation.

Yes they do, both give N * lambda = D * sin(phi)

The BaTh adds a .c/(c+v)...which is what is required.

No, the angle phi only tells you lambda_r, you have no
measure of v.

Study my diagram again George.

SR's one infers that the HST gratings would
NOT detect its own orbital movement.

Rubbish, don't try guessing Henry, you don't know
anything about SR so you're not going to get it right.
You know perfectly well that the conventional
grating equation is what I've shown above.

Wavelength of light is intrinsic and cannot change just because a grating is
moved somewhere, George.

That is your religion Henry, not reality.

The observed is never affected by the observer george.

SR says gratings are purely wavelength sensitive, George.
SR must be wrong.

Nope, the wavelength changes in reality.

It certainly might change after hitting the grating. So might the velocity...by
the same ratio. The frequency remains constant.


Dealt with three years ago, the incident light moves at
c wrt the mirror so the question is moot, the reflected
light also moves at c wrt the mirror whichever model
you adopt and the incident and reflected angles are
equal. The Sagnac experiment doesn't have a grating
in it so I don't know why you even mention that, seems
like you have lost the plot this time Henry.

Specular reflection is a limit case of grating diffraction.

OK.

My point is simply that you guessed what the
equation would contain rather than working it out.
When you got round to it, I'm sure it only took a
few minutes but you have now discovered that your
assumptions were inaccurate, speed does not
appear in the final equation, only the reflected
wavelength:

Lambda_r = D * sin(phi)

Can you not get it into you head George, lambda_i is universal and known.

Not according to ballistic theory. You still don't
understand the predictions of your own theory.

It doesn't affect the result if it DOES change during travel. Lambda_i/(c+vi)
is constant.

Angle phi depends only on lambda_r.

It depends entirely on Lambda_i and c+v/c+u

You also suggested it used the frequency but that
also isn't true because you don't know c+u which
is needed to get frequency from Lambda_r.

Assume u =0....although it might not be....

If it might not be then you can't assume, but even
if you do, you don't know v and you don't know
lambda_i or you wouldn't be trying to measure it
in the first place. The BaTh grating equation is:

Lambda_r = D * sin(phi)

That's all you can say.

I only need Lambda_e/(c+v).

You don't know v, angle phi depends _only_ on lambda_r
so that is what is measured, all else is conjecture.

You haven't studied the diagram George.


George



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