"Henri Wilson" HW@.... wrote in message
...
On Mon, 2 Apr 2007 22:29:54 +0100, "OG" wrote:


"Henri Wilson" HW@.... wrote in message
. ..
On Mon, 2 Apr 2007 19:06:42 +0100, "OG"
wrote:




Oh what a surprise, HW doesn't respond. Could it be he's wary of
reality?

Spectral lines don't measure OWLS, idiot.
Cut the insults if you want to be taken seriously.

Since spectral lines are narrow we know that all the light measured at
on
time was given off at the same point in the velocity-time cycle.

If some light coming from a cepheid was travelling faster than the rest
(as
you seem to be proposing) we would get broadening of the spectral lines.

Poor boy! You're not related to eric geese by any change, are you?

So what's your explanation then?

Explanation of WHAT? You haven't even described a problem yet.

You need it spelling out?

1 You seem to argue that the light we see from gas that is moving away from
us is coming towards us slower than light from gas that is coming towards
us.

2 You also seem to be saying that Cepheid variability is due to 'faster'
light catching up with (and adding to the brightness of) slower light as
stars move in binary orbits or expand/contract as Cepheids do.

3 Doppler shift - speed of emitting gas towards us or away from us changes
the wavelength of the light as we receive it. We can measure the motion of
the gas because spectral lines are narrow and the wavelength can be measured
precisely.

If 2 and 3 are true, then the spectral lines from cepheids _should_ show a
range of wavelengths representing the whole spread of speeds from the
fastest to the slowest at any one time. This range of speeds would be
greatest when the fastest was catching up the slowest (at maximum brightness
I assume)

4 However, we do not see broad spectral lines from cepheid variables - hence
at any one time the light that we are receiving was all emitted at the same
speed relative to us.

If you accept 3 and propose 1 to be true, and imply that 2 is a consequence
of 1, then observation 4 is a problem for you.