"Henri Wilson" HW@.... wrote in message
...
On Wed, 25 Apr 2007 09:16:22 -0600, Art Deco wrote:

Androcles wrote:

"bz" wrote in message
9.198.139...

At any speed below c, the grating will 'see' longer wavelengths as it
goes
away from the source.

Photons do not have wavelength anymore than cars so.
Roads have wavelengths, cars have frequency.

hahahahaahahahahahahahahahahhahahahahahaha

Good one, thanks.

Leave Andro alone. He's not as stupid as some others here.

There was an obvious typo in my last message. 'c' should have been 'v'.

This is what I was asking:

The equations for gratings include 'wavelength' and not light speed or
'frequency'. If a grating is used to inspect light coming from a star
moving at
v towards us, then the diffracted angles are indicative of the relative
speed
between the star and the grating.

If the grating is now moved away at 'v', why should those angles change?
Certainly the movement of the grating has not altered the light's
wavelength in
any way.

I smell a flaw in a theory somewhere.

The flaw is that you haven't applied ballistic theory yet,
you are assuming the conventional analysis. If the light
arrives at c and you move the grating at v then the relative
speed is c-v. The wavelength is the same so the frequency
drops. If the reflected signal is emitted at c relative to
the grating, then the reflected wavelength is increased to
c/(c-v) times the incident wavelength. If on the other hand
the reflected wave moves at c-v relative to the grating then
the wavelength stays the same as for the static grating, but
of course the speed is different. In both cases you need to
then work out the angle where the reflections are in phase.

George